US2552557A - Process of producing oxygen - Google Patents

Description

y 1951 F. J. JENNY ETAL PROCESS OF PRODUCING OXYGEN Filed Dec. 5, 1945 INVENTORS flan/i; J Jenny N m T T A Edward GKJo/zez'bel Patented May 15,1951

PROCESS OF PRODUCING OXYGEN Frank J. Jenny, New York, N. Y., and Edward G.

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

Application December 5, 1945, Serial No. 632,858

11 Claims.

This invention relates to the production of oxygen by the liquefaction and rectification of air, and more particularly to an economical methd of obtaining oxygen in high purity and in high yield without the use of chemical reagents to effeet the removal of carbon dioxide and moisture present in air.

All temperatures herein are in degrees F. and pressures 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 different pressures. The refrigeration necessery for liquefaction is supplied to the air after it has been compressed and water-cooled to approximately room temperature, by indirect heat exchange with the efiiuent products of rectification. However, an 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 refrigerantion heretofore used, involve compressing at least a portion of incoming air to pressures as high as 3000 pounds and expanding with or without the performance of work to produce a temperature drop; or compressing all the incoming air to about 600 pounds and after the air has been partially cooled by the products of rectification 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 counter-current 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 the apparatus.

More recently it has been suggested to use cold accumulators or regenerators (hereinafter referred to as heat exchangers) of large cold absorbing 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 these reversing heat exchangers in a, process in which the air is compressed to relatively high pressure results in more costly operation from the standpoint of horsepower requirements because upon every reversal, which may take place every three minutes, the volume of compressed air in the heat exchangers is lost and must be again replaced. Moreover, in the operation of such reversing heat exchangers it is important not to let the temperature at the exit end of the exchangers drop to a point where a part of the air becomes liquid because this liquid adheres to the surface of the exchangers and is Wasted upon reversal of flow. On the other hand the temperature conditions under which the exchangers are operated should be such as to obtain complete purging of the carbon dioxide deposited therein upon reversal of flow which usually requires having the air exit end of at least one of the exchangers at a low temperature, i. e., at or near the dew point of air.

It is an object of the present invention to pro- 'vide a processfor producing oxygen by the liquefaction and rectification of air in which moisture and carbon dioxide are removed from the air without the use of chemical reagents and which involves the use of reversing heat exchangers through which flow in heat exchange relation the outgoing products of rectification and the incoming air, the process being operated at relatively low pressures of the order of about 70 pounds to about 85 pounds gauge so that the loss of compressed air in the exchangers upon each reversal is small and in which the reversing ex- "changers are operated so that moisture and carment and power costs as compared with existing procedures. Other objects and advantages of this invention will be apparent from the following detailed description.

In accordance with this invention a stream of air at about 70 pounds to about 85 pounds gauge and a temperature of about '70 to about 110 F. is passed through a path in two or more heat exchange zones in series, each zone containing at least three fiow paths in heat exchange relation with each other through two of which pass respectively streams of oxygen and nitrogen products of rectification in heat exchange relation with the path through which the air is passing. One of the streams flowing between the first zone and a second zone 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 rectification withdrawn from the process and .for heat leaks into the system. The tempera- At the colder end of the second zone where the oxygen and nitrogen products of rectification enter and air leaves this zone, there is maintained between these products of rectification and the countercurrent stream of air a temperature difference in the range of about 5 to about F., preferably about 6 to about 8 F. This temperature difference is the difference between the temperature of the air and the weighted average temperature of the products of rectification, all temperatures being taken at the colder end of the second zone. For the purposes of this invention, the weighted average temperature of the products of rectification 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 of rectification and adding thereto the corresponding figure obtained by multiplying the temperature of the nitrogen product stream by its volume percentage. Thus, for ex- U ample, if the rectification 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 of the nitrogen stream temperature. Periodically the flow of air and nitrogen through their respective zones is reversed so that upon reversal the air flows through the paths through which during the preceding step the nitrogen had passed and the nitrogen flows through the paths through which had previously passed the air. The nitrogen removes, by sublimation, the carbon dioxide deposited during the preceding step in the second zone and the frost deposited during the precedingstep in the first zone.

Operating in this manner complete purging of carbon dioxide is obtained upon each reversal of flow. Likewise complete purging of frost is ob-. tained so that the equipment may be operated continuously.

Since the refrigeration necessary 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 is supplied at a point in the system where the temperature is relatively high, 1. e., the temperature may be of the order of about l35 F., it can be supplied economically, i. e., with low power cost. Operating within a temperature range of about F. to about 200 F. carbon tetrafluoride or ethylene may be used to supply the necessary refrigeration, or a minor portion of the compressed air, say about 7%, may be expanded for this purpose.

The apparatus required for the practice of the process is more economical and simpler than that required for priorknown processes in that the heat exchanger surface is reduced to a minimum and the need for caustic scrubbers, driers and compressors for high pressure air is eliminated. These economies in equipment and operating costs are obtained at no sacrifice to the oxygen recovery, or to purity of thedesired oxygen product; recoveries as high as 99% plus of substantially pure oxygen may be obtained when operating in accordance with the preferred embodiment of the invention. Recoveries as high as about 93% of the oxygen of the total air introduced into the process may be obtained in another embodiment in which the refrigeration is derived by expanding 7% of the air introduced into the system.

In the accompanying drawing Figure 1 illustrates diagrammatically the preferred layout of apparatus for practicing the process of this invention; and

Figure 2 shows afragmentary detail of the layout of apparatus of Figure 1, but in which instead of cooling the air stream fiowing from one exchanger to another, as in Figure 1, the nitrogen stream is cooled by the refrigerant.

In the drawing, the equipment shown for the practice 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/0r parallel, if desired, although this is objectionable from the standpoint of increasing construction costs, or the number of heat exchange paths in eachexchanger or zone may be increased over the 3-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.

In the drawing reference character l0 indicates a heat exchanger which may be of any well known type. In the embodiment shown on the drawings itconsists of a single shell in which are provided three flow paths, namely, interior path I I through which flows in one and the same direction throughout the operation of the exchanger the oxygen product of rectification. Paths I2 and I3 are providedwithin the shell of the exchanger through which periodically flow air and the nitrogen product of rectification in heat exchange relation with each other and with the oxygen. The heat exchanger has in each of the paths suitable fins of heat-conducting material, e. g., copper, promoting rapid and efficient heat exchange between' the gaseous media flowing therethrough. As theconstruction of. the heat exchanger per se does not form part of this invention and as it may be of any well known type, it is believed further description thereof is unnecessary.

The flow of the air and nitrogen through their respective paths is periodically reversed so that during one step of the process air flows through path 52 and nitrogen through path I3, and upon reversal, during the succeeding step air flows through path is and nitrogen through path l2.

Reversal of flow is accomplished by suitably positioning the compound reversing valves l 4 and 15 which may be of any well known type. Valve I4 is disposed in the pipe line system consisting of air inlet pipe l6 leading into valve I4, and pipe lines I! and i8 leading from the valve to cooling paths I2 and i3, respectively. At the base of the 'heat exchanger Hi lines I9 and 2!] are positioned leading from paths i2 and I3, respectively, to the valve I 5.

A second heat exchanger 2| is provided in the form of a shell havin therein paths 22, 23 and 24 provided with fins to promote heat exchange as in the case of the exchanger 10. Path 24 is the path through which the oxygen product of rectification flows from the rectification system hereinafter described to a pipe line 25 which communicates with path ll of heat exchanger Ill. The base portions of paths 22 and 23 of heat exchanger 2! communicate with pipe lines 26 and 21, respectively, which are communicably connected with a compound valve 28 which may be of the same type as valves M and H). At the upper portions paths 22 and 23 communicate respectively with lines 29 and 30 which in turn communicate with a compound reversing valve 3!. which may be of the same type as the other reversing valves.

Reversing exchangers Ill and 2| may be placed in vertical, horizontal or any other desired posiin indirect heat exchange relation with the nitrogen 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, 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 of rectif cation and for ,heat leaks into the system. In the preferred embodiment of the invention the air leaving the heat exchanger Ill is refrigerated to cause a drop of about 5 to about 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 pipe line 33 which passes through the refrigerator 32in indirect heat exchange with the refrigerant and communicably connects valves l5 and 28. Line 9 is the nitrogen line between the two heat exchangers Ill and 2 I.

Instead of refrigerating the nitrogen flowing .from heat exchanger 2! to heat exchanger l0 thereby introducing the cold supplied by the re- -Irigerating mediuminto the exchanger l0, Orin- -to cause the flow of the refrigerating medium stead of refrigerating the air flowing from heat exchanger Ill to heat exchanger 2|, the desired amount of refrigeration may be introduced into the system by expanding a portion of the air, say about 7%, of the total air introduced into the system. The cold expanded air thus produced may be introduced into the nitrogen stream entering the heat exchanger l0 thereby supplying the 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 cumbersome and expensive in construction and operation than an expander of the type suitable for expanding a relatively small amount of air at a relatively low pressure, e. g., '70-85' pounds gauge.

With the arrangement of valves and piping shown flow of nitrogen and air through heat exchangers it and 2! may be perodically reversedsay every three minutes-so that during an initial period of operation air flows through cooling path l2, through line l9, valve 15, refrigeration system 32 by way of line 33, valve 28, line 2%, cooling path 22 in heat exchanger 21, pipe line 29, valve 31 and thence to line 34 leading through the non-reversing heat exchanger 35 to the rectification system hereinafter described. At the same time, nitrogen flows through pipe line 36 leading from the non-reversing heat exchanger 35 into valve 3i, line 30, through path 23 in heat exchanger 2|, through line 21, valve 28, line Q, valve l5, pipe line 20, path 13 in heat exchanger l6, leaving this path through pipe line 98 and passing through valve I 4 to the atmosphere or other suitable disposal point. Upon reversal (as shown by dotted arrows and valve settings), the air flows through valve l4, line l8, cooling path it, pipe line 28, valve 55, refrigeration system 32 by way of line 33, valve 28, pipe line 21, and thence through the cooling path 23, leaving this cooling path through pipe line 33 and passing through valve 3,! and pipe line as into the non-reversing exchanger 35. At the same tune, the nitrogen flows from heat exchanger 35 through pipe line 36 into valve 3i thence through pipe line 23, path 22 in heat exchanger 2!, pipe line 25, valve 28, line 9, valve I5, line l9 into path 52, thence through line H into valve Hi and thence to the atmosphere or other suitable disposal point.

The rectification system comprises a. two-stage rectification column 3?, the lower section 38 of which is operated at a pressure of about 72 pounds gauge and the upper section 39 of which is opgrated at a pressure of from about 4 pounds to about 10 pounds gauge, preferably at about 5 pounds gauge. This column as is customary is provided with rectification plates of the bubblecap or other type. The lower section 38 .cf the column 3"." communicates with a condenser and has a liquid collecting shelf disposed iint'nediately below the condenser so for collectliquiol nitrogen. Pipe line 42 from this shelf 4! to a non-reversing heat exchanger 13 which in turn communicates through a pressure reducing valve M with the top portion of the Condenser ll! acts a reboiler From: therbase: portionwf. thelowerrsection 38 a:. pipe; line; 46 for; thedizow of'crude oxygen (containing: approximately 40% oxygen) passes toa non-reversing heat exchangerwhich communicates through1pipe; line 48 having a pressure reducing; valve 491therein-with the low-pressure sectionr33atan intermediate point indicatedby thereference character 50. A line having a pressure reducing valve- 52 therein, leads from condenserdfl'to anitrogen line 53 leading'to-the nonereversing -heat.exchanger 35; A- line, El i-leads fromthe top of low-pressure column 39 to:- the heat-exchanger. 43; they nitrogen flowing through this. line passing throughtheheat exchanger 43 then througlrline 55? and" heat exchanger 41' into line 56 which communicates with line 53. An oxygemlinelfl leads from the lower part of the low-pressure section: 390i column S'Z' to path 24 offheatexchangerfli. The heat exchangers 35, 4'3-and;4'|:- and the two-stage fractionating columnv3i-may be of any conventional type.

.Two separate fractionating columns, suitably interconnected, may be used inplace of the twostage column 3? shown. It will be understood that the equipment throughout is heat insulated to minimize loss of cold,

For a; desirable operating range, air at a pressure.of 70 pounds to 85 pounds gauge and a temperature of 70 to 110 F. is introduced into the cooling path in heat exchanger l0, leaving this path at a temperature of -120 to -l50 F., and substantially the same pressure. The nitrogen and oxygen products of rectification enter the heat exchanger ID at a temperature of -130 to 165 F. and leave at a temperature of 60 to 100 F. The air in passing from heat exchanger li! to heat exchanger 2| is refrigerated from 5 to F. so that it enters heat exchanger 2| ata temperature of 125 to 160 F. and leaves at a temperature of 260 to 280F. The nitrogen enters heat exchanger 2| at a temperature of 265-to 285 F. and leaves at a temperature of 130 to 165 F. The oxygen enters heat exchanger 2| at a temperature of -288 to 293 F. and leaves at a temperature of -130 to 165 F. The several streams suffer only a small pressure drop in flowing through the two reversing exchangers in series.

One example of the operation of the process of this invention is described below; it will be understood this example is given for purposes of exemplification 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 line |B, valve Hi and line H to heat exchanger l0, flowing through path |2 in which it is cooled to a temperature of -134 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 the path 22 of the heat exchanger 2| leaving this path at a temperature of 2"73 F. Substantially all moisture is removed in the form of frost in path |2 of heat exchanger l0 and all carbon dioxide is removed in solidified form in path 22. of heat exchanger 2|. The air. then flows through the heat exchanger 35 in heat exchange relation with nitrogen and enters high-pressure column 38 at a temperature of 275 F. and a pressure of 72- pounds.

Crude oxygen at a temperature ofv Z78 F. and, pressure of 7 2 pounds leaves the base of column.38, flows. through the heat exchanger 41 where its temperature .-is;reduced to I 286 F. and upon flow througnthepressure reducing valve 49 isflashed, entering lowrpressure column 39 ata temperature of 3l0 to 315 F. and a pressure of. 5--pounds.- Pure oxygen is withdrawn through line 51: at a-.temperature of -292 F. and a pres.- sureyofz5-pounds andflows through path 24, its temperature being increased to 146 F., the oxygen at'thiss temperature flowing through path ll of. heat exchanger I0, and bein withdrawn from this path" at atemperature of F. and, at a pressure; of;1 pound.

Nitrogenat-a temperature of about 286 F. andazpressure of '72 pounds is withdrawn through line 5| and'passes through valve 52, it tempera.- ture, being reduced; to a temperature of about 315. F. as'aresult'of the expansion through the pressurereducingvalve 5.2. Nitrogen at a temperature-of 315 F. and a pressure 0L5 pounds is withdrawn through line 54 and flows through heat exchanger 43 where its temperature is raised to about 30.42 F. The .nitrogen flows fromheat exchangen- 432 through heat exchanger 41. and mixes with that from-line, 5 the nitrogen stream thusproduced at a temperatureof 294 F. flows through line:.53.int.o andthrough heat exchanger 35:.where the temperature of the nitrogen is raised to Z78? F.. Thev nitrogen at this temperature and a pressureof: aboutv 5 pounds enters path 23 flowing; therethrough. in heat exchange relation with the-oxygenwhich enters at; a temperature of '292'F. and the air which, as above pointed out,. enters the base of? heat. exchanger 2| at 142F. and'leaves at a temperature of -273 F. AtithBCOIdBI. endofthe heat exchanger 2|, the nitrogen andthe oxygen streams have a weighted average-temperature of nearly -28l F. while at this point the air i at a temperature of "273." F. A temperature differenceofabout 8 F. is therefore: maintained. It will be noted that at the point where the air enters and the oxygen'and nitrogenleavethe heat exchanger 2| the difierence in temperature is approximately 4 F., the air-being ata temperature of 142 F. and the oxygenandnitrogen at 146 F.

From the heat exchanger 2| the nitrogen flows through line-21; reversing valve 28, line 9, reversingvalve I5; line 20 into and through path I3 in heat'exchanger' l0, entering this path at a temperature of: 146'F'. and leaving at a temperature of 90F. and a pressure slightly above atmospheric, sayl lipound gauge.

Upon reversal (as shown by dotted arrows and valvesettings), which may take place-every three minutes; the. air flows through the paths l3 and 2.3;:respectively; ofheatexchangers |0 and 2l and nitrogen flows through paths l2 and 22, respectively, of. heat: exchangers l0. and 2|. The flow is'otherwise' substantially the same and'the temperature; and:. pressure conditions remain the same. The nitrogen in its flow through path 22 of heat exchanger 2| removes by sublimation the carbon-dioxide deposited in thispath by the air duringzthe' preceding step. Likewise the nitrogen in its-flow through path I201 heat exchanger Ill removes from this paththe frost 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 frostdeposited in; the path through which the air had passed during the preceding step of the process- The.-exp ressions. reversing the flow of air and nitrogen? andreversal are used. herein in the sense commonly; employed. in. thisart, namely, to

mean the switching of the flow of two streams, for example, the air and the nitrogen streams, so that upon each reversal the air flows through the path through which had previously flowed the nitrogen, and the nitrogen fiows through the path through which had previously flowed the air.

It will be noted that this invention provides a process for producing oxygen of high purity without the use of chemical reagents which process may be operated continuously for long periods of time without shutdowns for the purpose of removing solid carbon dioxide or frost, which process is economical to operate particularly in that the 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 leaks into the system is supplied at a point in the process where the temperatures are relatively high so that it can be supplied efficiently and economically.

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:

1. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of air at about 7'0 to about 85 pounds gauge through a path in at least two heat exchange 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, the air thus being cooled to a temperature sufficient to substantially completely remove all moisture therefrom before the air leaves the first zone, cooling at least one of said streams during its flow between the first zone and the second zone, the cold thus introduced into the process compensating 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, regulating the fiow of air, nitrogen and oxygen into and from said second zone so that the temperature within said second zone is such as to effect substantially complete removal of carbon dioxide from the air in its passage through its heat exchange path in said second zone and the difference between the temperature of the air at the colder end of said second zone and the Weighted average temperature of the nitrogen and oxygen at the colder end of said second zone is within the range of from about to about 10 F., and periodically reversing the fiow of air and nitrogen through their respective paths in said zones, the air upon reversal flowing through the path through which had previously flowed the nitrogen and the nitrogen flowing through the path 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 as defined in claim 1, in which the stream cooled during its flow between the first zone and the second zone is the air stream.

3. A process as defined in claim 1, in which the stream cooled in its flow between the first zone and the second zone is the nitrogen stream.

4. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing air at about to about pounds gauge and a temperature of 70 to F. through one path in a heat exchange zone containing three paths in heat exchange relation with each other,

passing oxygen and nitrogen products of rectification, respectively, through the two other paths in heat exchange relation with the air, the air thus being cooled to a temperature sufficient to substantially completely remove all moisture therefrom, thereafter refrigerating the air leaving said zone, the amount of cold thus introduced into the air 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, then further coolin the air by fiowing it through one path in a second heat exchange zone containing three paths in heat exchange relation with each other, passing oxygen and nitrogen products of rectification, respectively, through the two other paths in said second heat exchange zone in heat exchange relation with the air and thereby cooling the air to a temperature sufiicient to remove substantially all carbon dioxide therefrom, passing the thus cooled air from the said second heat exchange zone to a rectification system in which the aforesaid oxygen and nitrogen products of rectification are formed, and periodically reversing the fiow or air and nitrogen through their respective paths in the said two zones, the air upon reversal flowing through the paths in the said two zones through which had previously fiowed 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 said second zone and the frost deposited in the said first zone during the preceding step of the process.

5. A process as defined in claim 4, in which the differential between the temperature of the air and the weighted average temperature of the oxygen and nitrogen at the colder end of the second zone is maintained within the range of about 5 to about 10 F.

6. A process for producing oxygen 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 one path in a heat exchange 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 heat exchange relation with the air, the air thus being cooled to a temperature of about to F., the moisture being thereby removed from the air, refrigerating the air leaving the first zone about 5 to 10 F., then further cooling the air by flowing it through one of the paths in a second zone, flowing oxygen and nitrogen products of rectification respectively through the other two paths in said second zone in heat exchange relation with the air thereby cooling the air to a temperature of about -260 to about 280 F., the differential between the temperature of the air and the weighted average temperature of the oxygen and nitrogen at the colder end of said assassv second zonebeing within the range of about to about F., and periodically reversing the flow: of airandnitrogenthrough their respective paths'in the 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 said second zone and the frost deposited in said first zone'during the-preceding step in the'process.

'7. A: processasdefined inclaim 6, in which the air leaving the first zone is refrigerated'by passage in heat exchange relation with liquid ethylene.

. 8. A process .forproducingoxygen by the liquefaction and rectificatiomof air, which comprises passingair under :pressure of about 75 pounds gauge and at a temperature of about 110 F. through a path in a'heat-exchangezone containing threepaths in "heat exchange relation with each other, passing oxygen and nitrogen products of rectification at a temperature of about 146 F. through the 'other two paths thereby coolingthe: air to a temperature otabout 134 F., passingthe :thus-cooledair in heat exchange relation *witha refrigerating medium and'thereby cooling: it to'ab'out -142 F., passing i the air at a temperature of about -142 F. through one ,path'in -a second heat exchange zonecontaining three; paths inheatexchange relation with eachothen-passing the oxygen product of rectification 311722.11 initial temperature of about 292 and the nitrogen product of rectification at an initial temperature of about *2'78" throughthe other two paths in said second zone in heat 'exchange relation with the air, whereby the air -.is-'cooled to a temperature of about 2'73 F. and the oxygen and nitrogen are heatedtoa temperaturerof about '146 F. upon leaving said. secondzone and substantially all carbon dioxide contained :inthe air is removed therefrom during its passage'through the secondzone, passing the air from the second zone'tc a rectification system, continu-ously flowing the oxygenthrough the same paths in the said two zones, -andperiodically reversing the flow of the air and-nitrogen sothatiupon reversal the air flows through the path through'which the nitrogen had flowed during the preceding step and the nitrogen flows through the path through which the air had'flowed during the preceding step whereby the nitrogen removes carbon dioxide and frost-depositedduring' a preceding step in the paths through which air had flowed during .the said preceding step.

.9. A process as defined in claim -8, in-which the refrigerating medium is ethylene.

10. A processforpproducing=oxygen by the liquefaction and rectification of air, which comprises passing astream ofair through a path in at least two heat exchange zones in series, passing a.stream-ofrectification product through another path in-said heat 1 exchange zones in heat exchange relation with the air passing therethrough, the air thus being cooled to a temperature sufficient to substantially completelly remove all moisture therefrom before the air leaves the first zone, cooling at least one of said streams during .its flow between the first 12 zone and thesecond zone, the cold thus introduced into the process compensating 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, regulating the flow of air and rectification product so that the'temperature within said second zone is such as to effect substantially complete removal of a condensible constituent from the air in its passage therethrough and the temperature difference-between the air leaving and the rectification product entering said second zone falls within the range of about'5 to about 10 F., and

7 periodically reversing the flow of air and rectification product through their respective paths in said second zone whereby upon each of said reversals the rectification product substantially completely removes the condensible constituent deposited during the preceding step of the process.

11. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of air at about '70 to about pounds gauge and a temperature of about 70 to about F. through a path in at least two heat exchange zones in series, passing a stream of rectification product throughanother .path in-said heat-exchange zones in heat exchange'relation with the air passing therethrough, the air thus being cooled to a temperature sufficient to substantially-completely remove all moisture therefrom before the air leaves the first zone,:cooling-at least one of said streams during its'flow between the first zone and the second zone, the'cold thus introduced into the process compensating for cold losses resulting from the difference in enthalpy between the air introduced into and the productsof rectification withdrawn from the process and for heatleaks into the system, regulating the flow of .air and rectification product into and .from said .second zone so that the temperature-within said. second zone is such as to effect substantially complete removal of carbon dioxide from theair in.its passagethrough said second zone and the temperature difference between the air leaving and the rectification product entering said second zone falls within the rangeofabout- 6 toabout 8 F., and periodically reversing theflow of air and rectification product through their respective paths in said second zone whereby upon each reversal the rectification product substantially completely removes the carbon dioxide deposited in said second zone during the preceding step of the process.

FRANK J. JENNY. EDWARD G. SCI-IEIBEL.

REFERENCES CITED The following references "are of'record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,057,804 Twomey Oct. 20, 1936 2,406,859 Trumpler Feb. 8, 1949 FOREIGN PATENTS Number Country Date 469,943 Great Britain Aug. 3, 1937

Claims (1)

1. A PROCESS FOR PRODUCING OXYGEN BY THE LIQUEFACTION AND RECTIFICATION OF AIR, WHICH COMPRISES PASSING STREAM OF AIR AT ABOUT 70 TO ABOUT 85 POUNDS GAUGE THROUGH A PATH IN AT LEAST TWO HEAT EXCHANGE 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, THE AIR THUS BEING COOLED TO A TEMPERATURE SUFFICIENT TO SUBSTANTIALLY COMPLETELY REMOVE ALL MOISTURE THEREFROM BEFORE THE AIR LEAVES THE FIRST ZONE, COOLING AT LEAST ONE OF SAID STREAMS DURING ITS FLOW BETWEEN THE FIRST ZONE AND THE SECOND ZONE, THE COLD THUS INTRODUCED INTO THE PROCESS COMPENSATING 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, REGULATING THE FLOW OF AIR, NITROGEN AND OXYGEN INTO AND FROM SAID SECOND ZONE IS SUCH AS TO EFFECT SUBWITHIN SAID SECOND ZONE IS SUCH AS TO EFFECT SUBSTANTIALLY COMPLETE REMOVAL OF CARBON DIOXIDE FROM THE AIR IN ITS PASSAGE THROUGH ITS HEAT EXCHANGE PATH IN SAID SECOND ZONE AND THE DIFFERENCE BETWEEN THE TEMPERATURE OF THE AIR AT THE COLDER END OF SAID SECOND ZONE AND THE WEIGHTED AVERAGE TEMPERATURE OF THE NITROGEN AND OXYGEN AT THE COLDER END OF SAID SECOND ZONE IS WITHIN THE RANGE OF FROM ABOUT 5* TO ABOUT 10* F., AND PERIODICALLY REVERSING THE FLOW OF AIR AND NITROGEN THROUGH THEIR RESPECTIVE PATHS IN SAID ZONES, THE AIR UPON REVERSAL FLOWING THROUGH THE PATH THROUGH WHICH HAD PREVIOUSLY FLOWED THE NITROGEN AND THE NITROGEN FLOWING THROUGH THE PATH 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.

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