US2537046A - Process for producing oxygen by the liquefaction and rectification of air - Google Patents

Description

Jan. 9, 1951 P. w. GARBO 2,537,046 PROCESS FOR PRODUCING OXYGEN BY THE LIQUEFACTION AND RECTIFICATION OF AIR Filed Feb. 24, 1949 2 n m a m T. m a a m WW 4 I Illlll UHF vm h lfl QNJ 1|- 2%- T KN. RR m, wl m IHIIHHI Nb mm HHI \& Q SQ 1 .q\ mmm HHHI & W N2 Patented Jan. 9, 1951 PROCESS FOR PRODUCING OXiGEN BY THE LIQUEFACTION AND RECTIFICATION OF Paul W. Garbo, Freeport, N. Y asslgnor to Hydrocarbon Research, Inc., New York, N. Y., a corporation of New Jersey Application February 24, 1949, Serial No. 78,118

8 Claims. 1

This invention relates to the production of oxygen'by the liquefaction and rectification of air in a rectification'system comprising low and high pressure stages.

All temperatures herein are in degrees 'F., pressures in pounds per square inch gauge, and percentages are by volume.

Oxygen processes are known which involve the flow of air under pressure through reversing exchangers in which the air recovers the cold content of the outgoing products of rectification and the thus cooled air is introduced'into the high pressure stage of the rectification system. In

such processes the air is thus cooled in the exchanger to a temperature close to its condensation point at the pressure existing in the reversing exchanger. The carbon dioxide present in the air is thereby substantially completely removed therefrom and deposited in the flow path in the exchanger through which the air flows. Periodically the flows of the rectification product and the air through the reversing exchanger are reversed through their respective flow paths. The rectification product stream then removes by sublimation the carbon dioxide deposited in the exchanger, thus purging same.

It is an object of this invention to provide a process for producing oxygen in which improved purging of the exchanger takes place.

Another object is to provide such process in which disturbance of the fractionating conditions within the rectification system is minimized.

Other objects and advantages of this invention will be apparent from the following detailed description thereof.

In accordance with this invention liquid from the high pressure stage of the rectification system is passed through at least the cold end of the reversing exchanger in indirect heat ex:- change relation with the air and/or rectification product passing therethrough. This liquid is caused to boil by the heat extracted from the gas stream or streams flowing in indirect heat exchange relation therewith and the, resultant vapors are expanded to produce refrigeration which is employed to compensate for enthalpy losses and for heat leaks into the system.

A specific embodiment of this invention involves the passage of air compressed to a pressure of 60 to 150, preferably 75 to 125, pounds per square inch and at a temperature of 50 to 110 F., preferably 60 to 80 F., through a reversing exchanger in indirect heat exchange relation with a stream of rectification product, e. g., nitrogen, the air being thus cooled to a temperature close to its condensation point. The reversing exchanger may be of either the regenerative or of the recuperative type. The thus cooled air is then passed to the high pressure stage of the rectification system and preferably brought into intimate contact with the crude liquid oxygen maintained in the lower portion of the high pressure column. The crude liquid oxygen, desirably after passage through a purification system which .eilects removal of residual carbon dioxide and any acetylene which may be present, is divided into two streams. One, the major stream consisting of from 90% to 95% of the liquid collected at the bottom of the high pressure column, is expanded and introduced as refiux into the low pressure stage. The other stream consisting of from 5% to 10% of the crude liquid oxygen collected at the bottom of the high pressure column is warmed by fiow through at least the cold end of the exchanger where the liquid is vaporized by heat exchange with the air and/or rectification product passing therethrough. Preferably, a stream of vapor of substantially the same composition as that of air and herein referred to as of essentially air composition, preferably withdrawn from the bottom portion of the high pressure stage, is employed as a carrier to effect introduction of the liquid into the exchanger. In this way droplets of the liquid are introduced into and caused to flow through a substantial portion of the flow path for the liquid through the exchanger before complete vaporization of the liquid is effected.

The resultant vapors admixed with astream of essentially air composition are introduced into an expander. 0f the total stream fed to the expander 10% to 25% by volume is derived from the liquid withdrawn from the bottom of the high pressure column. The remainder is a stream of essentially air composition, preferably, also derived from the high pressure column. The stream which is introduced into the expander and expanded to produce the refrigeration necessary to compensate for enthalpy losses and heat leaks into the system corresponds to from 15% to 35%, preferably 15% to 25%, of the amount of air fed to the process. The stream passing through the expander and thence introduced into the low pressure column is usually at least 10% richer in oxygen than ordinary air, since, as

. pointed out above, from 10% to 25% of this stream is derived from the crude liquid oxygen (generally about 35% to 40% oxygen purity) withdrawn from the bottom of the high-pressure column. As compared with prior procedures in 3 which a portion of cooled-air is expanded and the expanded air introduced into the low pressure column, the process of this invention, involving asit does the introduction of a vapor stream enriched in oxygen into the low pressure column.

results in less disturbance in the fractionating conditions within the low pressure column.

In the drawing forming a part of this specification the single figure illustrates aticallv a preferred layout of apparatus for practicing the process of this invention. It will be understood, however, this invention may be carried out in other apparatus than that shown in the drawing. For example, any dmired number of reversing exchangers may be used instead of the reversing exchanger shown in the drawing, each pair of reversing exchangers arranged in series may be replaced by one long exchanger, reversing exchangers of the regenerative type may be used in lieu of the reversing exchangers of the recuperative type illustrated diagrammatically in the drawing and other rectification systems may be used in lieu of that shown in the drawing including, for example, rectification systems in which separate columns are used for the low and high pressure stages.

Referring to the single figure of the drawing II is a recuperative heat exchanger which may be of any well-known type. In the embodiment shown in the drawing it consists of two sections II and II. Section II is provided with four fiow paths l3, l4, ll and It disposed in concentric relationship in heat exchange relation with each other. Section I: is provided with interior fiow path l1 and concentric paths is and II disposed in heat exchange relation with each other. The heat exchanger It has in each of the paths suitable fins of heat conducting material, e. g., coper or aluminum, permittin rapid and efilcient heat exchange between the gaseous media fiowing therethrollsh.

For purposes of illustration and in th interests of simplicity, each flow path is shown on the drawing as consisting of a single tube, the several paths being disposed concentrically. Actually. however, each path in each exchanger may comprise a multiplicity of tubes for fiow therethrough. As the construction of the heat exchangerpersedoesnotformapartofthisinvention and as it may be of any well known type, it is believed further description thereof is un- Path it is connected with path I by line II and path lswithpath it byline. 'Ihesepaths l8, I4 and I9, I! are the paths through which air and nitrogen fiow, the fiow of these two media through their respective paths being periodically reversed so that during one step of the process air fiows through paths I! and i3 and nitrogen through paths it and i4 and upon reversal during the succeeding step air flows through paths It and I4 and nitrogen through paths i and I3. Reversal offiow is accomplished by suitably positioning the reversing valves 23, 24 which may be of any well known type. Valve 23 is disposed in the pipe line system consisting of air inlet pipe 25 leading into valve 23, nitrogen exit line it leading to any suitable point of nitrogen disposal and pipe lines 21, II leadin to one end of paths. II and I. Lines 20 and lead from the fiow paths "and ll of section II tovalve It. Aline II leads from valve 24 through a non-reversing exchanger 1! to the high pressure stage it of the rectification system It hereinafter described and nitrogen line It leads into valve :4.

Plowpathsllandilarethefiowpaths through which oxygen fiows. These paths are interconnected by line 83. Flow path I1 is provided with an exit line 84 leading to a suitable point of oxygen storage or utilization and the flow path II is provided with an inlet line 3|. Flow of oxygen through fiow paths II and i1 continues unidirectionally, i.- e., fiow through these fiow paths is not reversed.

Flow path It is the fiow path into which a portion of the crude liquid oxygen from the base of the high pressure column is introduced, preferably admixed with a gaseous carrier stream of essentially air composition. The liquid thus introduced is vaporized and the resultant oxygenenriched air stream is warmed by flow through path It in indirect heat exchange relation with the air, nitrogen and oxygen flowing through their respective paths in section II. In this way the temperature approach between the temperature of the air leaving fiow path ll or II, as the case may be, and the temperature of the nitrogen entering one or the other of these fiow paths is brought within the range of 5 to 10 F., preferably 6' to 8 It, resulting in more efilcient purging of these fiow paths. Flow path It is rovided with an inlet line it and an exit line 31 assing to an expander 40, which may be a centrifugal expander or turbine of any well known type. A line 42 connects the expander with the low pressure stage of the rectification system 43.

Rectification system 43 comprises a two-stage rectification column, the lower section 44 of which is operated at a pressure of about to 150 pounds, preferably about to pounds, and the upper section 46 of which is operated at a pressure of about 4 to 12 pounds, preferably at about 5 to 8 pounds. This column, as is customary, is provided with rectification plates of the bubble cap or other desired type. The lower section 44 communicates with a condenser 48 which acts as a reboiler for the low pressure stage II. Condenser ll has a liquid collecting shelf 41 dis immediately below the condenser for llecting liquid nitrogen. Pipe line 48 leads from this shelf 41 to a non-reversin heat exchanger 4!. A line It provided with a pressure reducing valve ll leads from the nonreversing exchanger ll to the top of low pressure stage II.

Fromthebaseportionofthehighpressure stagellalinellleadstoalinetlcommunicating with a pair of liquid purifiers 84. II. A line II is communicably connected with the opposite ends of the purifiers I, It. Line I! is provided with a pair of valves l1 and It associated with purifier I4 and with a second pair of valves It, 0 associated with purifier ll. Line 60 is provided with a pair of valves ii, if associated with purifier H and a second pair of valves 83, ll associated with purifier ll. Only one of the purifiers l4, Ills placed on stream during operation. For example, valva II, II, Cl and 03 may be closed and valves BI and .2 opened so that fiow of crude liquid oxygen from line It takes place through purifier l4 and line ll. Simultaneously, purifier ll may be purged by passing a suitable purge medium, e. g., nitrogen or air, through the open valve '4 into and through the purifier II and through open valve I. When purifier 86 requires pur in valves ll, ll, .2 and M are closed and II, I! opened, thereby placing purifier II on stream. Purifier It may then be purged byopeningvalvestl andl'landpassingasuitable purge medium therethrough, as hereinabove described in connection with the purging of purifier 55.

Preferably each of the purifiers 54 and 55 consists of a bed 55 of granular silica gel adsorbent having superimposed thereon a iilter plate 66 for effecting removal of carbon dioxide particles from the crude liquid oxygen. This filter may be porous silicon carbide or porous metal. The silica gel acts to adsorb the acetylene dissolved in the crude liquid oxygen and the filter medium 55 to separate out the solid carbon dioxide. The silica gel adsorbent and the filter disposed in each of the purifiers 54 and 55 are preferably so proportioned that the filter and adsorber both require purging at about the same time. Instead of having the silica gel in one and the same unit with the filter 55, as shown in the drawing, separate units, one functioning to effect removal of acetylene and the other carbon dioxide from the liquid oxygen may be employed and these units may be designed to permit purging of each independently of the other.

A line 61 leads from line 56 and is provided with two branches 51a and 51b. Branch 51a leads to a non-reversing exchanger From exchanger 68 a line 59 having an" expansion valve therein leads to the low pressure stage 45 for introducing thereinto, as reflux, crude oxygen freed of acetylene and carbon dioxide. Branch 61b is provided with a valve 510 for controlling flow therethrough and communicates with line 36 leading into flow path l5. Thus from 10% to of. the crude liquid oxygen collected at the bottom of column 44 and freed of acetylene and carbon dioxide is introduced through lines 51b and 35 into flow path II.

From the top of condenser 45 a line H provided with an expansion valve 12 leads into nitrogen line 13 leading from the top of low pressure stage 45. Nitrogen line 12 leads into the nonreversing exchanger 49 which is connected by a nitrogen line 13a with non-reversing exchanger 68. Nitrogen line 32 leads from the exchanger '68 into reversing valve 24.

A line 14 leads from the base of the high .pressure column 44 just above the body of crude liquid oxygen therein and communicates with a pair of lines 15 and 15. Line 15 is provided with a valve 15a and communicates with line 31 leading into expander 40. Line 15 is provided with a valve 76a for controlling flow therethrough and communicates with line 35.

The base portion of low pressure column 45 is provided with an oxygen line 11 having a valve Ila therein for controlling flow therethrough. Line 11 leads into a non-reversing exchanger 15 from which line 35 leads into the ozwgen flow path l5.

In the operation of the equipment shown in the drawing, air is admitted through line 25, and, as indicated by the full line valve settings, fiows through line 28, flow path It, line 2|, flow path l3 in indirect heat exchange relation with nitrogen flowing through fiow paths M and I5 and I oxygen flowing through flow paths l5 and II. The air leaving flow path it through line 29 is thus cooled to a temperature close to its condensation point, at which temperature it enters valve 24 and fiows from this valve through line it and non-reversing heat exchanger It, and passes up through the body of crude liquid oxygen maintained at the base of the high pressure stage 44. The air bubbles through this crude liquid oxygen which effects removal of entrained carbon dioxide and acetylene from the air.

A minor portion of the liquid scrubbed air streemiswithdrawnfrcmthehighpressurecolumn 44 just above the body of crude liquid oxygen maintained therein through line I4 and is divided into two streams one of which passes through line 15 and the other through line 15. Crude liquid oxygen is continuously withdrawn through line 52, passed through one or the other of the purifiers 54, 55 which eifect removal of the carbon dioxide and acetylene contained therein and then flows through line 55 into line 51 where the thus purified liquid is divided into two streams. One the minor stream. consisting of from 5% to 10% of the liquid withdrawn from the high pressure column, flows through line 51b into line where it mixes with the air stream flowing through line It which functions as a gaseous carrier for the liquid in its flow through fiow path It introducing the liquid into this flow path in the form of mist or fine droplets. The remainder of the crude liquid oxygen passes through line 61a, exchanger 68 and line 59 and is flashed as it flows through expansion valve Ill into the low pressure stage 45.

The oxygen-enriched air fiowing through path I5 is warmed by the air fiowing in a countercurrent direction through fiow path It. The thus warmed oxygen-enriched air flows through line 31 where it mixes with the stream of essentially air composition fiowing through line 15. The resultant oxygen-enriched air stream enters expander 40 at a temperature such that liquefaction of the air in the expander does not take place. The expanded air flows through line 42 into the low pressure stage 45 of the rectification system at an intermediate point 42!: therein.

Liquid nitrogen flows from shelf 41 through line 45 into exchanger 49 where it is cooled by the nitrogen gas flowing through this exchanger. From this exchanger the cooled nitrogen fiows through line 55 and expansion valve 5| where it is fiashed and thus further cooled and enters the top of low pressure stage 45 where it serves as refiux liquid.

Gaseous nitrogen flows through line 13 into exchanger 49, thence through line Ila into exchanger thence through line 32 through reversing valve 24, line 35, flow paths l4 and i8, exiting through line 21, valve 23 and line 26. If desired, some nitrogen may be withdrawn from the high pressure stage 44 through line H, flashed as it flows through valve 12 and mixed with the nitrogen stream flowing through line I3. In this way incondensible gases tending to collect in the high pressure stage 44 may be purged therefrom.

Product oxygen fiows continuously from the low pressure stage 45 through line ll, exchanger 18 into line 35, fiow paths l5 and I1, exiting through line 34.

Upon reversal, which may take place every 3 to 15 minutes, as indicated by the dotted line valve settings, air fiows from line 25 through valve 23 into and through line 21, flow paths is and I4, while the nitrogen flows through fiow paths is and i9 and the oxygen flows through flow paths l5 and II. No reversal of flow of the oxygen or of the oxygen-enriched air stream passing through fiow path It takes place. The fiow of the various streams from the reversing valve 24 to the'rectification system 43, as well as the fiow of the various streams hereinabove described, within the rectification system and from the rectification system to the reversing valve 24 remains the same. on each reversal, the nitrogen efi'ects removal by sublimation and evaporation of carduring bon dioxide condensible impurities of air, e. g., moisture. depositedjin exchanger the preceding step f the process.

Instead of passing crude liquid oxygen in a carrier gas of essentially air composition through fiow path ii and admixing additional such gas from line II with the vapor stream flowing through line 21 and expanding this mixture in expander ll, only the crude liquid oxygen, preferably after removal of acetylene and carbon dioxide therefrom, may be passed through branch l'lb into line It and through flow path II where the liquid is vaporized. The resultant vapors are expanded in expander 40 and the expanded vapors introduced into the low pressure column II at a point substantially below point 42a where line 42 leads into the low pressure column. Usually the expanded vapor thus produced will provide only a portion of the refrigeration necessary to compensate for enthalpy losses and for heat leaks into the system- The remainder of the refrigeration necessary for this purpose, desirably, is provided by expanding the gas stream of essentially air composition withdrawn through line It in a separate expander and introducing the expanded air into the low pressure column 48 at a point somewhat above point 42a. Operating in this manner 10% to 25% of the total stream expended in both expanders is derived irom the crude liquid oxygen collected in the bottom of the high pressure column and the remainder from the air withdrawn through line 14.

One example of the operation or the process of this invention in apparatus of the type shown in the drawing is described below. It will be understood this example is given for purposes of exemplification only and the invention is not limited thereto.

This example refers to an oxygen plant operated in a locality where the atmospheric pressure is 14.7 pounds per square inch absolute. All

pressuresgiveaintheexampleareinpoundsper square inch gauge.

liirunderpressureofaboutsfipoundsandat a temperature of 60 F. is supplied to line II and fiows through valve 28. line 28, flow path ll, line 2!, flow path llrthe air is thus cooled to a temperature of 2'l4 I". The air then flows through reversing valve 24, exchanger ll into the high preuure stage II, the air entering this high premure stage at a pressure of about 83 pounds and at a temperature of 275 1'. The air bubbles through the body of crude liquid oxygen (containing approximately oxygen) maintainedinthebaseofthehigh pressurestage under pressure of about 88 pounds and at a temperature of -276 1'.

Crude liquid oxygen is withdrawn continuously through line I and passes through one or the other of the purifiers 84, ll which effects the removal of entrained carbon dioxide and acetylene. Of this crude liquid oxygen 1.3% fiows through line 01b at a temperature of 278 1''. intoline 3i, and thence through flow path ll of exchanger section II issuing therefrom into line 81 at a temperature of about -13 F. A stream of essentially air composition is withdrawn through line 14 at a temperature of -2'16 F. and apressure of about 82.5 pounds and fiows through line II into line 81 where it mixes with the oxygenenriched stream flowing through this line and thus produces a mixed stream at a pressure of about 82 pounds and a temperature of --242 1''. This mixed stream is expanded in expander ll producing an oxygen-enriched air stream (28.3%

oxygen content) at a temperature of -80l' 1'. andapressure ofabout9.4poundswhichisintroduced into the low pressure stage 4| through line 62 at 42c. Ofthe totalstreamfedtoexpander 4|, 14.6% is derived from the crude liquid oxygen collecting at the bottom of high Pressure column andtheremainderisthestreamof essentially air composition withdrawn throu line ll. Of the total air introduced into the process, 21.8% is expanded in expander Al to produce the refrigeration necessary to compensate forenthalpylossesandheatleabintothe system.

The remainder (92.7%) of the crude liquid oxygen flows through line l'ls. exchanger It, line ll and through expansion valve 10 where it is fiashedtoenterthelowpressurestagellua vapor-liquid mixture at a temperature of about 305' I". and a pressure of about 9 pounds.

Nitrogen is drawn from shelf 41 of h h pre sure stage M at a temperature of --283 1". throughlinellexchangerllandlineuami passed through expansion valve 8! into the top of low pressure stage ll at a temperature of about 3l3 I and a pressure or about 7.8 pounds.

Nitrogen at a temperature of 3l3 l". and a pressure of about 7.3 pounds fiows through line ls,iswarmedinexchangersllandtltoatemperature of -282 1''. at which temperature and a pressure of about 6.5 pounds it flows through valve 24, enters line 20 flowing through aths M and I8, exitmg through line 21, valve 22 and exit line 2 at a temperature oi 60' I". and at substantially atmospheric pressure.

Oxygen at a temperature of 288' F. and a pressure of about 10 pounds fiows through line 11 and exchanger II and enters fiow path II at a temperature of --282' I. In its fiow through fiowpaths II and lLtheoxygeniswarmedtoa temperature of I". at which temperature and :pressure of about 1 pound it exits through line Upon reversal. which may take place every five minutes, the air iiows through paths, II and M of exchanger sections it and II, respectively, and the nitrogen through paths I3 and il. The fiowofthevariousstreamsisotherwisethesame as hereinabove described and the temperature and pressure conditions remain the same. The nitrogen in its fiow through piths l2 and II removes by sublimation and evaporation the carbon dioxide and frost, if any, deposited in these pathsbytheairduringtheprecedingstepofthe process. Thus in the continued operation, the

nitrogen rectification product effects-removal of the carbon dioxide and frost, if any, deposited in the path through which the air has passed in the preceding step of the process.

In the operation of the process of this invention, it is preferred to effect removal of both moisture and carbon dioxide in the'reversing exchanger through which the air is passed. It will be understood, however, that, if desired, the moisture may be removed from the air by any conventional means and dry air containing carbon dioxide passed through the exchanger or exchangers as hereinabove disclosed. In the event dryairissuppliedtotheprocees,reversingvaive 21 may advantageously be moved to a position between exchanger sections l2 and II so that reversalotthefiowofairandnitrogentakesplace only in exchanger section II wherein the carbon dioxide is deposited by the air stream. Operation of such an arrangement is carried out so that the temperature at the warm end of ex- 8,587,048 9 l changer section II is at least slightly higher-than not of rectification and thus cool the air to a the temperature at which carbon dioxide begins temperature close to its condensation point, peto deposit from the air stream. In general, the riodically ers the flow of air and rectificawarm end of this exchanger should be at a temtion product through their respective paths in perature above about -1B0 F. 4 5 the reversing exchanger so that upon each of said The expressions "reversing th no of i and reversals the rectification product substantially nitrogen" and "reversal are used herein in th completely removes the carbon dioxide. deposited sense commonly employed in this art, namely, to in he r ing exchanger during the prece n mean the switching of the flow of two streams, s o the proc s. p n the thus cooled air for example, the air and the nitrogen or oxygen through a y of crude l quid o y en in he hi h rstreams, so that upon each reversal? the air pressure stage of the rectification system, confiows through the path through which had pretinuously passing a portion or the crude liquid viously flowed the nitrogen or oxygen and th oxygen into and through at least the cold end of nitrogen or oxygen flows through t t said reversing exchanger in indirect heat ex. through whi h ha previously flowed t change relation with the air and rectification It will be noted that i th proces of t product passing therethrough thus vaporizing vention liquid from the high pressure stage is said crude q d y en. expanding the resultant passed th h flo path to and 1 vaporized by vapors to produce refrigeration to compensate h at r d from t air stream flowin i'or enthalpy losses and heat leaks into the procthrough or as the case may be C55, and introducing the expanded vapors into the trogen stream passing therethrough. The inhringmg the temperature approach between the low pressure stage oi. the rectification system.

exiting stream and t incoming nitrogen 3. A process for producing oxygen by the liquestream within the range of 5a to F" prefers, faction and rectification of air in a rectification my 0 to with consequent improvement in system involving high and low pressure stages, the purging oi the flow path It or II by the niwhich comprises Passing stream of under pressure through a path in a reversing exchanger troductioh of liquid from the high pressure stage to recover the cold content of the outgolng'nitrointo flow path I reduces the cmss sect1oha1 area gen product of rectification and thus cool the air of the feed line to this how path and of the how to a temperature close to its condensation point, path itself, 1. e., the tubes o'r passages in the experiodichuy reversing the flow of air and nitrochanger through which the hquid flows. -Fun gen rectification product through their respective thermore, the use of such liquid results in better Paths in the reversing exchanger that 5 heat transfer conditions in the cold end of the each of said reversas the nitrogen substantially exchanger. Moreover, the expanded stream introduced into the/low pressure stage at 42a is enriched in oxygen and hence causes less disturbance of the fractionating conditions within this stage than would the introduction of a stream of expanded air. i

Since certain changes may be made in carry- 0 ing out the above processes without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in in the reversing exchanger during the preceding step of the process, passing the thus cooled air through a body of crude liquid oxygen in the high pressure stage of the rectification system, continuously passing a portion of the crude liquid oxygen into and through at least the cold end of said reversing exchanger in indirect heat exchange relation with the air and-nitrogen rectification product passing therethrough thus vaporizing said crude liquid oxygen, expanding the resultant vapors to produce refrigeration to coma :igig pensate for enthalpy losses and heat leaks into the process, and introducing the expanded vapors process for producing oxygen by the lime into the low pressure stage of the rectification faction and rectification of air in a rectification system column, which comprises, passing a stream of air 4 A process for producing oxygen by the homei iz g ig z g faction and rectification of air in a rectification c anger recover e con en an system involving low and high pressure stages,

going product of rectification and thus cool the which comprises passing a stream of under to a temperature close to its chhdehsahon pressure through a path in a reversing exchanger pomt' h h reversing the now air and to recover the cold content of the outgoing rectifiiahoh pmdhct through their respective stream or nitrogen rectification product and thus paths m h reversing exchanger that upon cool the air to a temperature closeto its coneach of ,sald reversals the rectification pmduct densation point, periodically reversing the flow of substantially completely removes the carbon air and nitrogen rectification product through oxide deposited in the reversing exchanger their respective paths in the reversing exchanger i preceding of the Process ihh'odhc' so that upon each of said reversals the nitrogen mg the thus cooled air into the rectification colsubstantially completely removes the carbon passing liquid from, d rectification dioxide deposited in the reversing exchanger umn into and through at least the cold end of during the preceding step of the process, passing d reversing exchanger in indirect heat the thus cooled air through a body of crude liqchange relation with the air and rectification m oxygen in t high pressure stage of t recth Product P n therethrough thus vaporizing fication system thus scrubbing said thus cooled d liq d. and xpa d the r s ltant vapors air with said crude liquid oxygen, withdrawing a to P odu refrigeratifln to pe e fo e minor portion oi. the crude liquid oxygenthalpy losses and heat leaks into the process. scrubbed air, passing a minor portion of said 2. A process for producing oxygen by the liquecrude liquid oxygen together with said minor faction and rectification of air in a rectification portion of the crude liquid oxygen-scrubbed air system involving high and low pressure stages, through at least the cold end of said reversing which comprises, passing a stream of air under exchanger in indirect heat exchange relation pressure through a path in a reversing exchanger with the air and nitrogen rectification product to recover the cold content of an outgoing prodto passing therethrough thus vaporizing the crude completely removes the carbon dioxide deposited.

1! liquid oxygen and producing a vapor stream enriched in oxygen. expanding the oxygen-enriched vapor. and introducing the expanded vapor into the low pressure stage of the rectification system.

5. A process producing oxygen as defined in claim 4, in which the vapor stream enriched in oxygen is at least 10% richer in oxygen than ordinary air.

8. A process for producing oxygen by the liquefaction and rectification or air in a rectification system involving low and high pressure stages, which comprises, passing a stream or air under pressure through a path in a reversing exchanger to recover the cold content 01' outgoing streams of oxygen and nitrogen rectification products and thus cool the air to a temperature close to its condensation point, periodically reversing the fiow of air and nitrogen rectification product through their respective paths in the reversing exchanger so that upon each or said reversals the nitrogen substantially completely removes the carbon dioxide deposited in the reversing exchanger during the preceding step of the process, passing the thus cooled air through a body of crude liquid oxygen in the high pressure stage of the rectification system thus scrubbing said thus cooled air with said crude liquid oxygen, withdrawing a minor portion of the crude liquid oxygen-scrubbed air, dividing said minor portion into two streams, continuously passing crude liquid oxygen from said body through a purification system which eflects removal of carbon dioxide from said crude liquid oxygen, dividing the purified crude liquid oxygen into two streams, expanding one of said streams and introducing the expanded stream as reflux into said low pressure stage, mixing the other liquid stream with one of the said'two streams of crude liquid oxygen-scrubbed air, passing the re sultant mixture through at least the cold end of said reversing exchanger in indirect heat exchange relation with the air and nitrogen rectification product passing therethrough thus vaporizing the crude liquid oxygen and producing a vapor stream enriched in oxygen, mixing the other of said two streams of crude liquid oxygenscrubbed air with the oxygen-enriched vapor stream, expanding the resultant mixture, and introducing the expanded mixture into the low pressure stage oi the rectification system.

7. A process of producing oxygen by the lique (action and rectification of air in a rectification system involving a low pressure stage and a high pressure stage, which comprises, passing a stream of air under a pressure or from 60 to 150 pounds per square inch gauge and at a temperature of from 50 to 110 1". through a path in a reversing exchanger to recover the cold content or an outgoing stream of nitrogen product oi. rectification and thus cool the air to a temperature close to its condensation point, periodically reversing the fiow of air and nitrogen rectification product through their respective paths in the reversing 12 exchanger so that upon each of said reversals the nitrogen substantially completely removes the carbon dioxide deposited in the reversing exchanger during the preceding step in the process. passingthethuscooiedairthroushabodyoi crude liquid oxygen in the high pressure stage oi the rectification system thus scrubbing said thus cooled air with said crude liquid oxygen, withdrawing a minor portion of the crude liquid l0 oxygen-scrubbed air, dividing said minor portion into two streams, continuously passing the crude liquid oxygen from the high pressure stage through a purification system which efiects removal of carbon dioxide from said crude liquid is oxygen, dividing the thus purified crude liquid oxygen into two streams. one consisting of approximately 90% to 95% or the crude liquid oxygen and the other consisting of from 5% to expanding the stream consisting of from 90% to 95% of the crude liquid oxygen to a pressure of from 4 to 12 pounds per square inch gauge, introducing the expanded stream as reflux into said low pressure stage, mixing the stream consisting of from 5% to 10% of the crude liquid oxygen with one of the said two streams of crude liquid oxygen-scrubbed air. passing the resultant mixture through at least the cold end or said reversing exchanger in indirect heat exchange relation with the air and nitrogen rectification product passing therethrough thus vaporizing the crude liquid oxygen and producing a vapor stream enriched in oxygen, mixing the other or said two streams oi crude liquid oxygen-scrubbed air with the oxygen-enriched vapor stream, expanding the resultant mixture to a pressure or from 4 to 12 pounds per square inch gauge, and introducing the expanded mixture into the low pressure stage of the rectification system.

8. A process for producing oxygen as defined in claim '7, in which from 15% to 35% of the air introduced into the process is expanded to produce the refrigeration necessary to compensate for enthalpy losses and heat leaks into the process and of the total stream ted to the expander from 10% to 25% is derived from the crude liquid oxygen collected in the high pressure stage.

PAUL W. GARBO.

REFERENCES CITED The following references are of record in the Name Date Trumpler Feb. 8, 1949 O'I'HERREFERENCES Air Purification in the Revising Exchanger, by hobo and Skaperdas, Transactions American In- Number 0 stitute Chem. Engrs, Feb. 1947, P e 69.

Low Pressure Liquefaction or Air, by Rushton, Relrlgerating Engineering, Jan. 1947, page 24.

Claims (1)

1. A PROCESS FOR PRODUCING OXYGEN BY THE LIQUEFACTION AND RECTIFICATION OF AIR IN A RECTIFICATION COLUMN, WHICH COMPRISES, PASSING A STREAM OF AIR UNDER PRESSURE THROUGH A PATH IN A REVERSING EXCHANGER TO RECOVER THE COLD CONTENT OF AN OUTGOING PRODUCT OF RECTIFICATION AND THUS COOL THE AIR TO A TEMPERATURE CLOSE TO ITS CONDENSATION POINT, PERIODICALLY REVERSING THE FLOW OF AIR AND RECTIFICATION PRODUCT THROUGH THEIR RESPECTIVE PATHS IN THE REVERSING EXCHANGER SO THAT UPON EACH OF SAID REVERSALS THE RECTIFICATION PRODUCT SUBSTANTIALLY COMPLETELY REMOVES THE CARBON DIOXIDE DEPOSITED IN THE REVERSING EXCHANGER DURING THE PRECEDING STEP OF THE PROCESS, INTRODUCING THE THUS COOLED AIR INTO THE RECTIFICATION COLUMN, PASSING LIQUID FROM SAID RECTIFICATION COLUMN INTO AND THROUGH AT LEAST THE COLD END OF SAID REVERSING EXCHANGER IN INDIRECT HEAT EXCHANGE RELATION WITH THE AIR AND RECTIFICATION

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