US2552558A

US2552558A - Process of producing oxygen

Info

Publication number: US2552558A
Application number: US632859A
Authority: US
Inventors: Frank J Jenny; Edward G Scheibel
Original assignee: Hydrocarbon Research Inc
Current assignee: Hydrocarbon Research Inc
Priority date: 1945-12-05
Filing date: 1945-12-05
Publication date: 1951-05-15
Anticipated expiration: 1968-05-15

Description

May 15, 1951 F. J. JENNY ET Al.

PRocEss oF PRonucING OXYGEN Filed Dec. 5, 1945 INVENTORS Patented May l5, `1951 PROCESS OF PRODUCING OXYGEN Frank J. Jenny, New York, N. Y., andEdward G.

Scheibel, Nutley, N. J., assignors to Hydrocarbon Research, Inc., New York, N. Y.

Application December 5, 1945, Serial No. 632,859

This invention relates to the production of oxygen by the liquefaction and rectification of air, and more particularly to the operation of the usual two-stage rectification column and associated heat exchangers.

All temperatures herein given are in degrees F. and pressures are in. pounds per square inch gauge.

Oxygen is commonly` produced by partial liquefaction of air and rectification at low temperatures; preferably rectification is conducted in two stages at diiferentpressures. The refrigeration necessary for liquefaction is supplied to the air after it has been compressed and watercooled to approximately room temperature, by indirect heat exchange with the effluent products of rectification. Howevenan additional amount of refrigeration must be, supplied to compensate for cold losses resulting from the difference in enthalpy between the incoming air and. the outgoing products of rectification and for heat leaks into the system. Methods of supplying this refrigeration heretofore used, involve compressing at least a portion of the incoming air to pressures as high as 300D pounds and expanding with or without the performance of work to produce a temperature drop; or compressing all the inf coming air to about 600 pounds and after the air has been .partially cooled by the products of rectiiication expanding a portion of the air. These methods are wasteful from the standpoint of compressor energy and require a great deal of equipment in the form of extra compressors, intercoolers and expanders.

For economical operation it is essential to recover the cold content of the outgoing products of rectification. This is usually accomplished by passing these products in heat transfer relationship with the incoming air. In older systems in order to avoid deposition of frost and solid carbon dioxide in the tubular countercurrent heat exchangers through which the air is passed in indirect heat exchange relation with the outgoing products of rectification, the air is treated in driers and caustic scrubbers to remove water and carbon dioxide prior to admittance of the air into the heat exchangers. Even with this treatment the exchangers had to be thawed out regularly to remove the frost (which term is used in a generic sense to` include both snow and ice) which caused stopping up of th@ apparatus.

More recently it has been suggested to use cold accumulators or regenerators (hereinafter referred to as heat exchangers) of large 4cold 6 Claims. (Cl. 62-175 .5)

absorbingv capacity through which the. warm incoming air and the cold products` of rectification are alternately passed with periodically reversed operation so that streams of warm air are flowed through the same packing filled spaces that the cold separated oxygen and nitrogen traversed during the previous step in the process, the high boiling impurities deposited. in these spaces during the passage of air therethrough being. removed by sublimation during the subsequent flow in a reverse direction of the products` of rectification. The use of thesereversing heat exchangers in a process in which the air is. compressed. to relatively high pressure results in more costly operationV from the standpoint of horsepower requirements because upon every reversal, which may take place every three minutes, the volume of compressed air in the heatexchangers is lost and must be again replaced.

In copending application Serial No. 632,858 filed December 5, 1945, there is disclosed and claimed a. process for producing oxygenby liquefaction and rectification of air involving the flow of air at about 'l0` to about 85 pounds at a temperature of about to about 110 li'. through the heat` exchange paths Yof two` orY more reversing heat exchangers in series, `each exchanger containing two other paths through which` are passed respectively streams of oxygen and nitrogen products of rectification in heat exchange relation with the air passing therethrough. The airstream flowing from the rst exchanger to the second is refrigerated, the amount of cold thus introduced into the process being adequate` to compensate for cold. losses resulting from the difference in enthalpy between the air introduced into and the products of rectication withdrawn from the process and for heat leaks into the system. The temperature conditions in the first exchanger are such that substantially all: moisture present in the air is removed therefrom in the` form of frost. The temperature conditions in the second exchanger are such as to effect substantially complete removal of carbon dioxide from theiair in its passagetherethrough.

At the colder end of the second exchanger where the oxygen and nitrogen products of rectication enter and air leaves the exchanger, there is maintainedbetween these products of rectification and the countercurrent stream of air a temperature difference in the range of about 5 to about 10 F., preferably about 6 to about 8 F. This temperature difference is the difference between the temperature of the air and the weighted averagetemperature of the products of 3 rectification, all temperatures being taken at the colder end of the second exchanger. For the Y purposes of this invention, the weighted average temperature of the products of rectication is calculated by multiplying the temperature of the oxygen product stream by the volume percentage of the stream based on the combined volume of the products Vof rectification and adding thereto the corresponding ligure obtained by multiplying the temperature of the nitrogen product stream by its volume percentage. Thus, for example, if the'rectication system is operated to produce two streams of substantially pure oxygen and pure nitrogen, the weighted average temperature of the two streams would be approximately the sum of of the oxygen stream temperature and 80% of the nitrogen stream temperature. Periodically the flow of air and nitrogen Ythrough their respective paths in the two exchangers is reversed so that upon reversal the air flows through the paths in the two exchangers through which during the preceding step the nitrogen had passed and the nitrogen ilows through the paths in the two exchangers through which had previously passed the air. The nitrogen removes, by sublimation, the carbon dioxide deposited during the preceding step in the second exchanger andthe frost deposited during the preceding step in the rst exchanger.

Operating in this manner complete purging of carbon dioxide is attained upon each reversal of ilow; Likewise complete purging oi frost is obtained so that the equipment may be operated continuously.

This invention is in the nature of an improvement on the invention disclosed and claimed in the aforesaid copending application.. It is an object of this invention to effect removal of incondensibles, such as hydrogen, helium and neon, from the rectification system without reduction in the yield of oxygen recovered in the process.

panded to cool the same and the cold thus produced imparted to the rectification products entering the low-pressure stage and preferably also to the air entering the high-pressure stage. Periodically the ilow of air and nitrogen is reversed through their respective paths in the two zones, the air upon reversal flowing through the paths through which had previously owed the nitrogen and the nitrogen ilowing through the `paths through which had previously flowed the air, whereby upon each reversal the nitrogen substantially completelyV removes the carbon dioxide A further object is to increase the efficiency of Y the operation of the rectication system. Other objects and advantages of this invention will be apparent from the following detailed description.

In accordance with this invention a stream of air is passed through a path in two zones in series, each of the zones containing at least three paths in heat exchange relation with each other and streams of oxygen and nitrogen rectification products are passed through the other two paths inthese zones in heat exchange relation With/the air passing therethrough. One of the streams is cooled in its now between the first and second zones to a temperature suilicient to supply to the system the necessary cold to compensate for cold Vlosses resulting from the diierence in enthalpy Abetween the incoming air and the deposited in the second Zone during the preceding step of the process.

In the preferred embodiment of the invention, a minor portion of the nitrogen withdrawn from the high-pressure Ystage of the rectification system is passed through the second zone where the nitrogen is heated by the air stream flowing to the high-pressure stage of the rectification system. The heated nitrogen is then mixed with the remainder of the nitrogen withdrawn from the high-pressure stage of the rectication system thereby increasing the temperature of the nitrogen, preferably not more than 20 F., and the mixed nitrogen stream thus introduced into the expander at a temperatureV such that no liquid nitrogen is formed within the expander with consequent improvement in the Vefdciency oi the operation of the expander. i f

In the preferred embodiment illustrated inthe drawing, the single iigure of which illustrates diagrammatically a preferred layout of apparatus for practicing the process of this invention, the yequipment shownfor the practiceY of the process involves a pair of heat exchangers having an ethylene refrigeration system for refrigerating the air and the present description will be confined to the present illustrated embodiment of the invention. It will be understood, however, that the process may be carried out in other equipment, for example, each of the two exchangers in series may be replaced by two or more smaller exchangers placed in series and/or parallel, if desired, although this is objectionable from the standpoint ofincreasing construction costs, or the number of heat exchange paths in each exchanger may be increased over the 3- outgoing products Vof rectication and for heat leaks'into the system. The temperature difference between the temperature of the air leaving and the temperature of the rectification products entering the second Zone is maintained withinV j the range of from about 5 to about 10 F. and the exit temperature of the air leaving this zone is such as to eiect substantially complete removal of carbon dioxide from the air in its passage through its path in this zone. From this second' zone the air is'passed tothe high-pressure stage of a two-stage rectification system in indirect heat exchange relation with rectification prod- Y ucts from the low-pressure stage of the system.

' part of this invention and as it may beV ofY anyV well-known type, it isbelieved further descrip-- path construction shown in the drawing, or other refrigeration systems may be employed in lieu of the ethylene system. Hence, the scope of the invention is not confined to the embodiment herein described. Y

In the drawing reference character .lil ndicates a heat exchangerwhicli may be Yof any well-known type. In the embodiment shown in the drawings it consists of a single shell in which are provided three paths, namely, interior path li through which flows in one and the same direction throughout the operation of the exchanger the oxygen `product of rectification.

YPaths I2 and I3 are provided within the shell Y oi the exchanger Ythrough which periodically flow air and the nitrogen product of rectication in heat exchange relation with each other and with the oxygen. The heatexchanger has in each of the paths suitable fins ofheat-conducting material, e. g., copper, promoting rapid and efficient heat exchange between the gaseous media ilowing therethrough. As the construction Vof the heat exchanger per se does not Vform tion thereof is unnecessary.

The flow of the air'and nitrogen through their respective. paths is periodicallyf reversede so, that during, one step of` the; processair flows through path I2 and nitrogenthroughpath. I3, and upon reversal, during the succeeding step air flows through path I3` and4 nitrogen through path I2.

Reversal of now is` accomplished by suitably positioning the compound reversing valves I4 and I5 which may be of any well-known type. Valve I4 is disposed in the pipe line system consisting of air inlet pipe I5 leading into valve I4, and pipe lines I'I and I8 leading from the valve to cooling paths I2 and I3, respectively. At the base of the heat exchanger If lines I!)` and are positioned leading from paths I2` and I3, respectively, to the Valve I5.

A second heatexchanger 2I is provided in the form cf a shell having therein

paths

22, 23 and 24 provided with iins to promote heat exchange as in the case; of the exchanger Ill. Path 24, is.` the path through which the oxygen product I of rectification flows :from` the rectification system hereinafter described to a pipe line 25. which communicates with path I I of heat exchanger I3'. The base portions of

paths

22 and 23 of heat exchanger 2| communicate with pipe lines 26 and 2, respectively, which are communicably co-nnected with a compound valve 28 which may be of the same type as4 valves I4 and I5. At the

upper portions paths

22 and 23 communicate respectively with

lines

29 and 33 which in turn communicate with a compound reversing valve 3l which may be oi the same type as the other reversing valves.

Reversing exchangers II! and2| may be placed in vertical, horizontal or any other desired position. Likewise, when these exchangers are arranged vertically, the colder end may be above or below the warmer end.

A refrigeration system 32 of any well-known construction. for supplying a refrigerating medium, such as ethylene, or carbon tetraiiuoride is provided for cooling either the nitrogen flowing from heat exchanger 2I to heat exchanger IB, or the air flowing from heat exchanger IE! to heat exchanger 2 I. This refrigerating system operates t;

to cause the now of the refrigerating medium in indirect heat exchange relation with the ntirogen or air to be cooled, the rate of flow and temperature of the various media being so controlled that enough cold is introduced by refrigeration, I

at this point in the process, to compensate; for cold losses resulting from the difference in enthalpy between the incoming air and. the outgoing products oi rectification and for heat leaks` into the system. In the preferred embodiment of the inventionV the air leaving the heat exchanger II! is refrigerated to cause a drop oi about 5 to about l0" F. in its temperature; this has been found adequate for the purposes above stated. Refrigeration of the air is accomplished by causing it to flow through pipeline, 33 which passes through the refrigerator 32 in indirect heat exchange with the` refrigerant and comcunicably connects valves I5 and 28. Line 9 is the nitrogen line between the two heat exchangtem. The. coldexpanded: air thus produced` may be introduced. into the nitrogen stream entering theheat exchanger Iii thereby supplyingthe necessary cold to compensate. for cold losses resulting from the difference in enthalpy between. the incoming air and the outgoing products of rectification and for heat leaks into the system. This latter method has the disadvantage that. it involves a loss of approximately 7% of the oxygen content of the air introduced. into the system. On. the other hand it has the advantage that it eliminates the necessity for using a refrigeration system for cooling either the nitrogen` or air, which system is more cumberf some and expensive` in construction and, operation than an expander of the type suitable for expending. a relatively small amount of air ata relatively low pressure, e. g'., 70-85 pounds gauge.

With the arrangement of values and piping shown flow of nitrogen and. air through heat exchangers III and 2| may be periodically reversed, say every three minutes, so that during an initial period of operation air 'lows through heat exchange path I2, through line I3, valve I5, refrigeration system 32A by way of line 33, valve 2.3, line 25, cooling path 22 in heat exchanger 2i, ypipe line 29, valve 3l and thence to line 34 leading through the non-reversing heat exchanger 35 tov the rectication system hereinafter described. At the same time, nitrogen flows through pipe line 35 leading from the non-re versing heat exchanger 35 into valve 3l, line 33, through path 23 in heat exchanger 2l, through line 21, valve 28, line 9, valve I5, pipe line 23; path I3; in heat exchanger I0, leaving` this. path through pipe line- I8 and passing through valve I4 to the atmosphere or other suitable disposal point. Upon reversal (as shown by dotted arrows and valve settings), the air flows through valve I4, line I8, path I3, pipeline 23, valve I5, refrigeration system 32 by way of line 33, valve 28, pipe line 2, and thence through the cooling path 23, leaving` this cooling path through pipe line 3l] and passing through valve 3| and pipe line 34A into the non-reversing exchanger 33. At the same time, the nitrogen Hows from heat exchanger 35. through pipe line 36. into valve 3l, thence through pipe line 29, path 22 in heat exchanger 2|, pipe line 26, valve 28, line 3, valve I5, line I9 into path I2, thence through line I? into valve I4 and thence to the atmosphere or other suitable disposal point.

The rectiiication system comprises a two-stage rectication column 37, the lower section 38 of which is operated at a pressure of about l2 pounds gauge and the upper section 39 of which is operated ata pressure oi from about 4 pounds to about l0 pounds gauge, preferably at about 5 pounds gauge. This column as is customary is provided with rectification plates of the bubble-cap or other desired type. The lower section 38 of the column 31 communicates with a condenser 4U and has a liquid collecting shelf 4I disposed immediately below thecondenser i3 for collecting liquid nitrogen. Pipe line 42 leads from this shelf 4I to a non-reversing heat exchanger 43 which in turn communicates through a pressure reducing valve 44 with the tcp por tion of the upper section 33 as indicated by the reference character 45. Condenser 43 acts as a reboiler for the upper section 39 of the column 31. Y

From the .base portion of the lower section-i 38 a pipe line 4B Vfor the flow of crude oxygen (con .f taining approximately 49%- oxygen) passes to a non-reversing heat exchanger ,41 which communicates with pipe line 48 havingV a pressure reducing valve 49 therein with the 10W pressure section 39 at an intermediate point indicated by the reference character 50. Line I leads from the top of the condenser 40 and has a regulating valve 52 therein. This line communicates with an expander 53 which discharges by way'of. line 53a into line 54 hereinafter described. Preferably, there is also provided a branch line 53 having a regulating valve 59 and leading to a path 6U disposed in heat exchanger 2| in indirect heat exchange relation with the oxygen, nitrogen and air passing through the other three paths in this exchanger 2 I'.V A line 6| leads from path 60 back to line 5|. Regulating valves 52 and 59 disposed in lines 5I and 58, respectively, regulate the portions of the nitrogen streamllowing from the condenser 40 which are passed directly to expander 53 and indirectly through path Vlill of exchanger 2|. Y

By the arrangement of lines hereinabove described Va minor portion `of the total nitrogen introduced into the process passes through line 5| and, preferably, of the portion thus Withdrawn a minor portion, say about 10%, passes through linev 58, path 69 and line 6| entering line 5| where it mixes with the remainder of the nitrogen withdrawn from the condenser 40. IThe portion of nitrogen p-assing through path 60 is warmed up by indirect heat exchange, and by mixing with the remainder of the nitrogen, the stream entering expander V53 is at a temperature suilcient to avoid condensation or formation of liquid nitrogen in the expander. In a preferred embodiment of the invention from about 1% to about by volume of the total nitrogen introduced into the process and containing incondensibles, such as hydrogen, helium and neon, is passed through line 5| and of this quantity about 10% by volume passes through heating path 60 and 90% by volume continues through line 5|.

The nitrogen stream refrigerated as a result of the expansion flows from the expander 53 to a line 53a which meets line 54 conveying the nitrogen stream leaving the top of low-pressure section 39. The mixture then flows through heat exchanger 43 in indirect heat exchange relation with the nitrogen passing through this exchanger and thereafter flowing through reducing vvalve 444 into the top of low-pressure section 39. From Vheat exchanger 43 the mixed nitrogen stream flows through line 55'into.and through heat exchanger 41 where it flows in indirect heat exchange relation with the crude oxygen flowing therethrough to low-pressure section 39. From the heat exchanger 41 the mixed nitrogen stream passes through line 59 into and through heat exchanger 35 where it passes in indirect heat exchange relation with air flowing into and from this exchanger, by way of line 34. From the heat exchanger 35 the nitrogen stream flows through line 35 into a compound valve 3|, thence through

path

22 or 23, as the case may be, of heat exchanger 2|, through valves 28 and I5 connected by line 9, then through path I2 or I3 of heat exchanger I0V and finally through compound valve I4 tothe atmosphere; the flow throughV path I2 0r VI3 of heat exchanger II) depending upon the setting of valves |4'and `I5 and the

lowthrough path

22 or 23 of heat exchanger 2| depending upon the setting of Yvalves 28 and 3| as hereinabove described in connection with the operatio of these reversing heat exchangers.

, The

heat exchangers

35, 43 and 41 and the twostage fractionating column 31 may be of any conventional type. Two separate fractionating co1- umns, suitably interconnected may be used inY place of the two-stage column 31 shown. It will be understood that the equipment throughout is heat insulated to minimize loss of cold.

One example of the'operation of the process of this invention is described below. It will be understood this examples given for purposes of exemplication only and the invention is not limited thereto.

Air under pressure of about 75 pounds gauge and temperature of about 100 F. is supplied through lineIS, valve I4 and line I1 to heatV exchanger |0, flowing through path I2 in which it is cooled to a temperature of 134.5 F. The air then flows in indirect heat exchange relation with ethylene in the refrigeration system 32 and is cooled thereby to a temperature of 142 F., then passes through path 22 of the heat exchanger Y 2| leaving this path at a temperature of 275 F.

Substantially all moisture is removed in the form of frost in path I2 of heat exchanger Id and all carbon dioxide is removed in solidied form in path 22 of heat exchanger 2 I. The air then flows through the heat exchanger 35 in heat exchange relation with nitrogen and enters high-pressure column 36 at a temperature of 278 lFrand aV pressure of 72 pounds. f;

Crude oxygen at a temperature of 280 F. and a pressure of 72 pounds leaves the base of column 39, flows throughV heat exchanger. 41 wher its temperature is reduced to 289 F. and upon flow through the pressure reducing Valve '59 is ashed, entering low-pressure column 39 at a temperature of 310 to 315 F. and a |pressure of 5 pounds. Pure oxygen is withdrawn through line 51 at a temperature of 292.5 F.

and a pressure of 5 pounds and'rfiows through a path 24, its temperature being increased to 146 F., the oxygen at this temperature entering path II of heat exchanger I0 and being withdrawn from this path at a temperature of 90 F. and at a pressure of 1 pound.

Nitrogen at a temperature of Vabout 286.5 F. and a pressureroif 72 pounds-in amount equal to 12.5% by volume of the totalrnitrogen introduced into the process is withdrawn through line 5|. Of the nitrogen owing through line 5I, 10%

' passes through line 58 and path 69, its tem-pera- Y through exchanger 43 in indirect heat exchange relation with nitrogen employed as Vreiiux V.in column 39, its temperature being thereby increased 'to 306 F. while the Vtemperature of nitrogen flowing through line 42 (pressure of Y '12 pounds) Vand exchanger 43 is reduced to 300 Ff This nitrogen by expansion through valve 44 has its pressure reduced to 5 pounds and its temperature to 315.5 F. The nitrogen product of rectification then ows through heat exchanger 41 Where its temperature is increased to 293 F. The crude oxygen stream owing through exchanger 41 is thereby cooled from a temperature of 280 F. to a temperature of -:289 F. The Anitrogen then flows through exchanger 35 in heat exchange relation with the fair, the nitrogen stream temperature Abeing thereby .increased to 279 at which temperature it Venters the heat exchanger 2l, `:flows therethrough and is thereby heated `to 146 F. At the colder end of the heat exchanger 2l., the nitrogen and the oxygen streams have a `weighted average temperature of nearly 282 F. while at this point the air is at a temperature Yof 275 F. A temperature differenceoi about '7 F. is therefore maintained. It will be noted that at the point where the air enters fand the `oxygen and nitrogen leave the heat exchanger 2l the diierencein temperature is approximately 4 F., the air being at a temperature of 142 F. and the oxygen and nitrogen at 146 F.

From heat exchanger -2I the nitrogen flows through heat exchanger S where it is `heated to 90 F. The nitrogen at `this temperature and a `pressure slightly above atmospheric, say 1 pound gauge, may `he vented to the atmosphere thereby venting the incondensibles, such as hydrogen, helium and neon, removed .from the .high-pressure stage of the rectification system.

'Ihe desired -oxygen product is withdrawn through line 51 `at a temperature of -292.5 F.

and `pressure of pounds, flows `through heat exchanger 2l where its temperature is increased to -146 F. and then through heat `exchanger l0 where its temperature is `increased to 90 F. The oxygen leaves exchanger I0 at a pressure of 1 pound.

Upon reversal (as shown by dotted arrows and valve'setting-s) which may take place every three minutes, the air flows through paths IS and 23, respectively, of heat exchangers l0 and 2l and nitrogen hows through paths VI2 land V22respectively,.of heat exchangers i0 and 1l. The now is otherwise substantially the same and the temperature and pressure conditions remain the same. The nitrogen in its now through path 2-2 of heat exchanger 2| removes by sublimation the carbon dioxide deposited in this `path by the air during the preceding step. Likewise, the nitrogen in its ow through path l2 of Lheat exchanger I removes from thispath the fr-ost deposited 'therein from the air during the preceding step. Thus in the continued operation upon each reversal the nitrogen effects removal of the carbon dioxide and frost deposited in the paths through which the air had passed during lthe preceding step of the process.

Operating in accordance with this invention it is found possible to recover substantially 100% of the oxygen content `introduced into the rectification system in the form of substantially pure oxygen and at the same 'time effect continuous Ip1,1i'ging from the high-pressure stage of the rectification system of the incondensible constituents, such as hydrogen, helium and neon. .Further the purging is carried out so as to increase the eiliciency of the rectication system in that the nitrogen stream containing the incondensibles is expanded and therefrigeration thus produced employed to cool thereflux oxygen and nitrogen introduced into the low-pressure stage and the air introduced `into the high-pressure stage.

The expressions reversing the low of `air and nitrogen and "reversal are used herein in the sense commonly employed in this art, namely, to mean the switching o1" the ow oi two streams, for example, the air and the nitrogen streams, so that upon each ,reversal the air owslthrough 10 "the rpath through which had previously flowed the nitrogen, and the nitrogen flows through `the path through which had previously iiowed the air.

It will be noted this invention provides a process for producing oxygen of high ,purity without the use of chemical agents, which process may `loe operated continuously `over a long period of time without Vsluit-downs for the `purpose of removing solid carbon dioxide or frost, which process is economical to operate, particularly in that Vthe refrigeration which must be supplied to compensate for cold losses resulting from the difference in enthalpy 'between incoming air and. the outgoing products of rectification and for heat leaksiinto the system is supplied at a point .in the process where the temperatures are relatively high so that it can be supplied `eiiiciently and economically, and which process effects continuous purging from the high-pressure stage of the rectification system of the incondensible constituents, such as hydrogen, helium and neon, so as to increase the eiiiciency of the rectification system.

Since certain changes may be made in carrying out the above process 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 a. limiting sense.

What is claimed is:

l. A process for'producing `oxygen by the lique- `faction and rectification of air, which vcomprises passing a stream of air through Aa path in two zones in series, each of said zones containing at least three paths in heat exchange relation with each other, passing respectively streams of oxygen and nitrogen. products of rectification through two other paths in said zones in heat `exchange relation with the'air passing therethrough, cool- `ing at least one of `said streams during its now between the first zone andthe second Zone, withdrawing the air from the second zone at a temperature such that substantially all carbon dioxide in said air has been removed from the air in its passage through its path in said second Zone, maintaining the temperaturediference between the temperature of the air leaving and `the weighted average temperature of the nitrogen and oxygen entering said second Zone so that it ifalls within the range or from about 5 to about 10 F., passing the air from said second zone to the high-pressure stage of a two-stage rectication system in indirect heat exchange relation with a rectication product from the low-pressure stage of said system, withdrawing a minor portion of the nitrogen from the high-pressure'stage, expanding the nitrogen thus withdrawn to cool the same, imparting the cold thus produced to the rectification products entering the low-pressure stage, periodically reversing the flow of air and nitrogen through their respective paths in said zones, the air upon reversal flowing through the paths through which had previously flowed the nitrogen and the nitrogen owing through the paths through which had previously flowed the air, whereby upon each reversal the nitrogen substantially completely removes the carbon dioxide deposited in said second zone during the preceding step of the process.

2. A process for producing oxygen by the liquefaction and rectiication of air, which comprises passing a stream of air at about '70 pounds to about pounds gauge and a temperature of about '70 to about 110 F. througha path in two least three paths in heat exchange relation with each other, passing respectively streams of oxygen and nitrogen products of Yrectification through two other paths in said zonesl in heat exchange relation with theair passing therethrough, cooling at least one ofY said streams during its ow between the rst zone and the second zone, the amount of cold thus introduced into the process being adequate to compensate for cold losses resulting from the difference in enthalpyY between the air introduced into and the products of rectification withdrawn from the process and for heat leaks into the system, withdrawing the air vfrom the second' zone at a temperature such that substantially all carbon dioxide in said air has been removed from the air in itsV passage through its path in said second zone, maintaining the temperature difference between the temperature of the'air leaving and the Weighted average temperature of the nitrogen and oxygen entering said second zone so that it falls within Vthe range of from about to about 10 F., passing the air from said second zone to the high-pressure stage of a two-stage rectication system in indirect heat exchange relation with a rectification product from the low-pressure stage of said system, withdrawing a minor portion of the nitrogen containing incondensible gases from the high-pressure stage, expanding the nitrogen thus withdrawn to cool the same, passing the expanded nitrogen in heat exchange relation with nitrogen and oxygen supplied as reflux to the low-pressure stage and with air supplied to the high-pressure stage, and periodically reversing the iiow of air and nitrogen through Y their respective paths in said zones,.the air upon reversal flowing-through the paths in the two zones through which had previously flowed the nitrogen and the nitrogen flowing through the paths through which had previously owed the air, whereby upon each reversal the nitrogen substantially completely removes the carbon dioxide deposited in the second Zone during the preceding step of the process.

3; A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of air at about '70 pounds to about 85 pounds gauge and a temperature of about 70 to about 110o F. through a path in two zones in series, each of said Zones containing three paths in heat exchange relation with each other, passing respectively streams of oxygen and nitrogen products of rectication through the two other paths in said zones in heat exchange relar tion with the air passing therethrough, cooling at least one of said streams during its flow from one zone to the other, the amount of cold thus introduced into the process being adequate to compensate for cold losses resulting from the difference in enthalpy between the air introduced into and the products of rectification withdrawn from the process and for heat leaks into the system, withdrawing the air from the second zone at a temperature such that substantially all carbon dioxide in said air has been removed from the air in its passage through its path in said second zone, maintaining the temperature difference between the temperature of the air leaving and the weighted average temperature of the nitrogen and oxygen entering said second Zone so that it falls within the range of from about 5 to about 10 F., passing the air from said zones to the high-pressure stage of a two-stage rectification system in indirect heat exchange relation with a rectification product from theVlow-pressure stage of said system, withdrawing from the high-pressure stage about 1% to 15% of the Y total nitrogen introduced into the process, said nitrogen containing incondensible gases, heating approximately 10% of the nitrogen thus withdrawn, mixing the heated nitrogen with the re'- maining 90% of the nitrogen thus withdrawn thereby yielding a nitrogen stream having a temperature sufliciently highto avoid the formation of liquid nitrogen infthe expander,V expanding said nitrogen stream, passing the expanded nitrogen in heat exchange relation with oxygen and nitrogen supplied as reilux to the low-pressure stage and with the Vlair supplied to the highpressure stage, and periodically Vreversing the flow of air and nitrogen through their respective Y pathsV in said two zones, the air upon reversal flowing through the paths in the two YZones through which had previously flowed the nitrogen and the nitrogen iiowing through the paths in the said two zones through which had previously flowed the air, whereby upon each reversal the nigtrogen substantially completely removes the carbon dioxide deposited in the second Zone during the preceding step of the process.

4. A process for producing oxygenY by the liquefaction and rectification of air, which comprises passing air at about 70 to about 85 pounds gauge and a temperature of about 70 to about 110 F. through a path in a Zone containing three paths in heat exchange relation with each other, flowing oxygen and nitrogen products of rectification respectively through the` other two paths in said Zone in heat exchange relation Vwith the air, the air thus being cooled to a temperature sufficiently low to deposit out as frost substantially all the moisture in the air, refriger-ating the air leaving the rst zone to lower its temperature about 5 to 10 F., then further cooling the air by flowing it through a path in a second zone containing three paths, flowing oxygen and nitrogen products of rectication respectively throughY the other two paths in said second zone in heat exchange relation with the air thereby cooling the air to a temperature suiiiciently low to deposit out substantially all the carbon dioxide in the air, the differential between the temperature of the air and the weighted average temperature of the oxygen and nitrogen at the colder end of said second zone being within the range of about 5 to about 10 F., passing the air from said zones to the high-pressure stage of a two-stage rectification system in indirect heat exchange relationwith a rectification product from the lowpressure stage of said system, withdrawing from 1% to 15% of the total nitrogen introduced into the process from the high-pressure stage of the system, said nitrogen containing incondensible gases, expanding the stream of /nitrogen thus withdrawn, mixing the expanded nitrogen with a stream of nitrogen withdrawn from the lowpressure stage and passing the resultant nitrogen in heat exchange relation with nitrogen and oxygen fed to the low-pressure stage and air fed to the high-pressure stage, and periodically reversing theY flow of air and nitrogen through their respective paths in the said two zones, the

air upon reversal flowing through the paths inA upon each reversal the nitrogen substantially.v

assasse faction and rectification of air, which comprises passing a stream of air through a path in two zones in series, each of said Zones containing three paths in heat exchange relation with each other, passing respectively streams of oxygen and nitrogen products of rectification through the two other paths in said zones in heat exchange relation with the air passing therethrough, thereby cooling the air leaving said second zone to a temperature suflicient to remove substantially all carbon dioxide therefrom the carbon dioxide thus removed being deposited in said second zone, cooling at least one of said streams during its flow from one zone to the other, the amount of cold thus introduced into the process being adequate to compensate for cold losses resulting from the difference in enthalpy between the air introduced into `and the products of rectification withdrawn from the process and for heat leaks into the system, passing the airfrom said second zone to the high-pressure stage of a two-stage rectification system, lwithdrawing from said high-pressure stage nitrogen containing incondensible gases, heating by indirect heat exchange with the air passing through said second zone the nitrogen thus withdrawn to a temperature suciently high to avoid the formation of liquid nitrogen upon expansion of said nitrogen, expanding said nitrogen, passing the expanded nitrogen in heat exchange relation with oxygen and nitrogen supplied as reflux to the low-pressure stage of said rectification system, `and periodically reversing the low of air and nitrogen through their respective paths in said two zones, the air upon reversal flowing through the paths in the two `zones through which had previously flowed the nitrogen and the nitrogen flowing through the paths in the said two zones through which had previously flowed the air, -whereby upon each reversal the nitrogen substantially completely removes the carbon dioxide deposited in the second zone during the preceding step of the process.

6. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of air at about 70 pounds to about 85 pounds gauge and a temperature of about 70 to about 110 F. through a path in two zones in series, each of said zones containing three paths in heat exchange relation with each other, passing respectively streams of oxygen and nitrogen products of rectification through the two other paths in said zones in heat exchange relation with the air passing therethrough, thereby cooling the .air leaving said second zone to a temperature sufficient to remove substantially all 14 carbon dioxide therefrom the carbon dioxide thus removed being deposited in said second zone, cooling at least one of said streams during its flow from one zone to the other, the amount of cold thus introduced into the process being adequate to compensate for cold losses resulting from the difference in enthalpy between the air introduced into and the products of rectification withdrawn from the process and for heat leaks into the system, passing the air from said second Zone to the high-pressure stage of a two-stage rectication system in indirect heat exchange relation with a rectification product from the 10W- pressure stage of said system, withdrawing from the high-pressure stage fromV about 1% to about 15% of the total nitrogen introduced into the process, said nitrogen containing incondensible gases, heating a minor portion of the nitrogen thus withdrawn by indirect heat exchange with all of the air passing to the high-pressure stage of the rectification system, mixing the heated nitrogen with the remainder of the nitrogen thus withdrawn, thereby producing a nitrogen stream having a temperature sufficiently high to avoid the formation of liquid nitrogen upon expansion, expanding said nitrogen stream, passing the expanded nitrogen in heat exchange relation with oxygen and nitrogen supplied as reflux to the lowpressure stage and with the air supplied to the high-pressure stage, and periodically reversing the flow of air and nitrogen through their respective paths in said two zones, the air upon reversal flowing through the paths in the two zones through which had previously flowed the nitrogen and the nitrogen flowing through the paths in the said two zones through ywhich had previously flowed the air, whereby upon each re- -versal the nitrogen substantially completely removes the carbon dioxide deposited in the second zone during the preceding step of the process.

FRANK J. JENNY. EDWARD G. SCHEIBEL REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,539,450 Wilkinson May 26, 1925 1,607,322 Van Nuys Nov. 16, 1926 2,057,804 Twomey Oct. 20, 1936 2,422,626 Koehler June 17, 1947 2,460,859 Trumpler Feb. 8, 1949 FOREIGN PATENTS Number Country Date 373,918 Great Britain June 2, 1932 469,943 Great Britain Aug. 3, 1937

Claims

1. A PROCESS FOR PRODUCING OXYGEN BY THE LIQUEFACTION AND RECTIFICATION OF AIR, WHICH COMPRISES PASSING A STREAM OF AIR THROUGH A PATH IN TWO ZONES IN SERIES, EACH OF SAID ZONES CONTAINING AT LEAST THREE PATHS IN HEAT EXCHANGE RELATION WITH EACH OTHER, PASSING RESPECTIVELY STREAMS OF OXYGEN AND NITROGEN PRODUCTS OF RECTIFICATION THROUGH TWO OTHER PATHS IN SAID ZONES IN HEAT EXCHANGE RELATION WITH THE AIR PASSING THERETHROUGH, COOLING AT LEAST ONE OF SAID STREAMS DURING ITS FLOW BETWEEN THE FIRST ZONE AND THE SECOND ZONE, WITH DRAWING THE AIR FROM THE SECOND ZONE AT A TEMPERATURE SUSH THAT SUBSTANTIALLY ALL CARBON DIOXIDE IN SAID AIR HAS BEEN REMOVED FROM THE AIR IN ITS PASSAGE THROUGH ITS PATH IN SAID SECOND ZONE, MAINTAINING THE TEMPERATURE DIFFERENCE BETWEEN THE TEMPERATURE OF THE AIR LEAVING AND THE WEIGHTED AVERAGE TEMPERATURE OF THE NITROGEN AND OXYGEN ENTERING SAID SECOND ZONE SO THAT IT FALLS WITHIN THE RANGE OR FROM ABOUT 5* TO ABOUT 10* F., PASSING THE AIR FROM SAID SECOND ZONE TO THE HIGH-PRESSURE STAGE OF A TWO-STAGE RECTIFICATION SYSTEM IN INDIRECT HEAT EXCHANGE RELATION WITH A RECTIFICATION PRODUCT FROM THE LOW-PRESSURE STAGE OF SAID SYSTEM, WITHDRAWING A MINOR PORTION OF THE NITROGEN FROM THE HIGH-PRESSURE STAGE, EXPANDING THE NITROGEN THUS WITHDRAWN TO COOL THE SAME, IMPARTING THE COLD THUS PRODUCED TO THE RECTIFICATION PRODUCTS ENTERING THE LOW-PRESSURE STAGE, PERIODICALLY REVERSING THE FLOW OF AIR AND NITROGEN THROUGH THEIR RESPECTIVE PATHS IN SAID ZONES, THE AIR UPON REVERSAL FLOWING THROUGH THE PATHS THROUGH WHICH HAD PREVIOUSLY FLOWED THE NITROGEN AND THE NITROGEN FLOWING THROUGH THE PATHS THROUGH WHICH HAD PREVIOUSLY FLOWED THE AIR, WHEREBY UPON EACH REVERSAL THE NITROGEN SUBSTANTIALLY COMPLETELY REMOVES THE CARBON DIOXIDE DEPOSITED IN SAID SECOND ZONE DURING THE PRECEDING STEP OF THE PROCESS.