US1498766A

US1498766A - Method and apparatus for separating the constituents of gaseous mixtures

Info

Publication number: US1498766A
Application number: US465518A
Authority: US
Inventors: Claude C Van Nuys
Original assignee: Air Reduction Co Inc
Current assignee: Airco Inc
Priority date: 1921-04-29
Filing date: 1921-04-29
Publication date: 1924-06-24
Anticipated expiration: 1941-06-24

Description

June 24. 1924; 1,498,766

- C. C. VAN NUYS- METHOD AND APPARATILSMFOR SEPARATING THE CONSTITUENTS OF GASEOUS mx'ruazs Filed April 29. 1921 avwmtoz A Gama 1 Patented dune p i To on whom it may concern onaunn 0. van nu'ys, orcnam'onn new arnnsnr, assreiron 'ro fie fnnnucrron' COMPANY, rnconronn'rnn, aconro'rron or Y y at are v tremolo .arrnnarus non snr nannies.

Application filed Apri129, leer." Serial no. 485,518.

. Be it known" that I, CLAUDE C. VAN Now, a citizen of: the United States, residing at Cranford, in the county of Union, State of New Jersey, have invented certain new and useful Improvements in Methods and Apparatus for Separatin the Constituents of -Gasous Mixtures; an I do hereby declare the'following to be a full, clear, and exact description of the invention, such" as will enable others skilled inthe art to which it appertains to make and use" thesame.

This invention relates to the liquefaction and separation of gaseous -mixtures having three constituents for the purpose of recovering such constituents in a theoretically and commercially economical manner. The .method employed is particularly adaptable for the separation (if the constituents of air, although it may be applied for that purpose to any ternary niinturewith constituents, the boiling points of which" are each dltierent from the others.

It has been proposed heretofore, and cominercial methods are. now operated, to'sepa- A rate by liquefaction and subsequent rectification, the constituents ot'a pernary gaseous mixture suchas atmospheric air, which for the purpose of this disclosure, is considered to be composed of oxygen, nitrogen and argon, thereby disregarding the minute uantities of rare elements resent. Meth- 'ods asheretofore racticed have, however,

I relatively low eficlency when compared to the theoretical possibilities. For example, suchmethods as practiced heretofore employ eight to ten times as much energy as that theoretically required toseparate the constituents in substantial purity, and it has.

been found impossible to actually recover more than one constituent in suitably pure condition Thus, in all these liquefaction methods forthe separation. of air, if it is desired to. produce substantially pure oxygen, .it is found "impossible torecover more than to 7 5% of the ,oxygen contained in the air treated. For the purpose of increasing from the standpoint of the amount of energy expended and the percentage of-re- 'covery of the constituents, an extensive study of the various methods heretofore the e'ficiency" of air-separation, bothpracticed has been undertaken with theresults hereinaiterset forth.

' It isthe object, therefore, of the invention to eliminate many of the sources of energy loss in methods as heretofore practiced, by I avoiding as far as possible all thermodynam ically irreversible operations in connection with the production ot the refrigeratiye efi'ect required in the liquefaction cycle, and

A. further object of the inventionnis the provision of a method of and apparatus for the production of argon from the atmosphere in an economical and efic'ient manner ,accompanied by the recovery of oxygen of higher purity than has heretofore been pee-- sible indiqireiaction operations owing to the difiiculty, experienced in separating argon therefrom. r

vention will be apparent as it is better un- Further objects and advantages of the ink derstood by reference to the'iollowing specification and accompanying drawing dia-v grammatically illustratin an apparatus which is adaptedfor use 1n practicing the invention. It is to be understood that in the drawing no attempt has been made to illustrate those details of liquefaction apparatus which are well known tothose skilled in the art, the purpose of the drawing being merelyis the separation of the three constituents in CA distinguishing feature of the invention 7 three successive steps, each one of these 1-- steps employing ordinary processes of separation.

The first step consists air to be treated into two parts by means of selectively liquefying a portion or it, employing for that pu'rpose'to the'greatest possible degree, the well known method of backward return. This step results inthe separation of a fraction, consisting approximately of half is volume of the air treated,

in- Ste-ma an the and-composed substantially pure gaseous nitrogen, the other portion being a ternary 'mixture of nitrogen, oxygen and argon in liquid condition, the percentages of the two latter constituents being substantially greater than for atmospheric air, e. g., xygen 45%, argon 2% and nitrogen 53%. The pure nitrogen fraction, which is available at substantially the original pressure of the compressor, is not further treated, but after being brought into contact with succeeding portions of the incoming air, is employed as 'a working fluid in an expansion engine, or

' what enriched in argon, while the other contains from 93 to 95% oxygen and approximately half of the argon contained in the original air. The sub-portion of approximate air composition is brought into contact by means of suitable interchangers with the incoming air in order to cool the air, and is thereby restored to substantially the original air temperature. It is then either returned directly to the main air compressor, or in case the operation is such that it has sutficient pressure, it is expanded in an engine or motor, and after assisting to cool the incoming air, it is returned to the air compressor and thence back to the liquefaction" cycle.

The sub-portion of% to 95% oxygen is available in the liquid state according to the method herein described and is delivered to an intermediate point of an auxiliary rectification column, in which the third and last step of the separation process is accomplished, this'consisting in the production of oxygen of high purity in a liquid condition, and an argon product containing a small amount of oxygen and onlyea very minute quantity, if any at all, of nitrogen. A small amount of substantially pure nitrogen is also separated in this step, which is returned at a suitable level-to the primary rectification column by means of which the second separation is accomplished.

Inorder that the various advantages of this method may be pointed out and comparisons made with methods heretofore practiced, reference is made, to a well-known method, which has been in extensive commercial use for the production of oxygen and argon from atmospheric air. In the latter method, atmospheric air is'compressed to a pressure of substantially 30 atmospheres in a two orJ-three stage compressor provided with inter-coolers and after-coolers supplied finest ea with water, and is thereafter cooled in interchangers by indirect contact with gases resulting from'the separation. A portion of the cooled air is conveyed to a liquefierwhere it is further cooled and liquefied in toto, i. e., non-selectively, by indirect con tact with the cooled separated gases before It then passes into a pot at the base of the primary rectification column, and thence upward through tubes of a backward return" condenser, and is therein selectively liquefied by'indirect contact with liquid oxygen resulting from rectification as hereinafter de scribed, the latter being evaporated around the tubes at a somewhat lower pressure than that of the air in the tubes.

The resultof this selective liquefaction of the engine exhaust is to separate it into two portions, one of which consists of substantially pure nitrogen, which is subsequently liquefied by indirect contact with evaporating liquid at a higher level in the rectification column, while the other consists of a a liquid of substantially 45 to 47% oxygen purity. The liquid air produced in the liquefier is added to the enriched liquid and the combined liquid is conveyed upwardly through a pipe having a pressure-reducing valve and is discharged into the rectification compartment of the main column where it cascades over rectification trays of the usual form. The liquid nitrogen produced as just described, is conveyed through a similar pipe and pressure-reducing valve into the rectification column at a point near the top.

Liquid oxygen of to 97% purity collects at the bottom of the primary rectification column. Nitrogen containing substantial amounts of oxygen escapes at the top of the column, and after passing through 1 the liquefier and temperature exchangers in order to cool the incoming air, is rejected. In the actual operation of the method here referred to,1 this waste nitrogen carries from 5 to 8% oxygen and over half of the argon contained in the air treated.

The 95 to 97% liquid oxygen which collects at the bottom of the primary rectification column is led through a pipe and delivered in the liquid state to an intermediate pointof an auxiliary rectification column, in which it cascades over rectification trays of the usual form, and thereby has its oxygen percentage increased still further by contact with vapors ascending in said column.

weaves As the high purity oxygen liquid collects at the bottom of the auxiliary column, it is vaporized by coming into' indirect co itact with low purity vapors contained in the tubes of the condenser portion of the auxiliary column, these vapors being the efiluent from the top of the auxiliary column after compression in an auxiliary compressor subsequent to circulating in heat exchanging re-' lation with the compressed gas delivered by that auxiliary gas compressor. The compressed gas, after passing from thecompressor through the interchanger just. de-

scribed, is delivered to a pot at the base of the auxiliary column and thence passes upward through tubes of the auxiliary condenser, being selectively liquefied therein, a small amount of substantially pure nitrogen being abstracted from the top of the tubes and delivered to a suitable level in the main rectification column.

The liquid produced in the tubes of the auxiliary condenser collects in the bottom of the pot just described and passes upward.

through a pipe and pressure reducing valve and is delivered to the top tray'of the aux-- iliary rectification column, Where it serves as a reflux liquid for the vapors rising above the admission level of the oxygen liquid coming from the primary rectification column as already described.

When a suitable purity of argon product is attained in the auxiliary compressor cycle just described, limited quantities of this product are abstracted from the auxiliary cycle at the point of entrance of the gases to theauxiliary compressor, and conducted to a suitable holder or container. The high purity liquid oxygen evaporated from around the tubes ofthe auxiliary condenser, and constituting the oxygen product, is conducted hack through the liquefier and interchanger of the primary column, and thence to. a suitable gasometer or container.

. It is evident from the foregoing descri tion that since the liquid product or t e liquid necessary to be returnedfrom the auxiliary to the primary column is derived indirectly from the'auxiliary column by evaporating the excess liquid therein by means II" this precaution "a vaporizing coil, which-is located in'the lower liquid reservoir of the auxiliary column and in which unseparated air circulates,

being non-selectively liquefiedmore or less completely therein. This unseparated air is obtained by dividing the exhaust air leaving the expansion engine into two portions, one of which goes direct to the tubular condenser or the primary column as already described, while-the other portion is conducted through the vaporizingcoil of the auxiliary column as just stated. This portion'oi' the engine exhaust evaporates the excess liquid of the auxiliary column, and after complete or partial non-selective liquefaction, passes toan upper level of the primary rectification column, where it is mixed with the descending liquid derived from the tubes of the primary condenser and from the liquid coming from the liquefier.

It is thusapparent that the operation of the auxiliary column requires a greater amount of air to be diverted to the liquefier than would be necessary if the auxiliary cycle were absent, thus reducing the amount passing to the expansion engine, and furthermore, requires-a diverting of a substantial portion of the expansion engine exhaust tothe vaporizing coil of the auxiliary column; lihe only portion of air which is selectively liquefied by backward return is that portion which passes direct from the expansion engine exhaust to the main tubular condenser. The operation of the auxihary column thus very much reduces the amount of pure nitrogen liquid available forfrefiux liquid at the top of the pri- I mary rectification column, and it'is found that the liquid nitrogen available for that purpose is much too small for the requirements. This condition tends to he aggravatedin the operation of. this method by reason of the fact. that it is difiicult to insure that all of that portion of the engine exhaust'passing throu h the vaporizing coil in the auxiliary con enser. is liquefied in that coil, since in orderto-make the boiling.

efi'ect of the coil sufiiciently vigorous there is a strong tendency on the part of the operator' to. open the valve. controlling the flow. through this coil to a point where vapor, as well as liquid, leaves saidooil to be delivered to the primary column rectifier. Thepresence of this vapor requires an increased. amount of reflux nitroged liquid in order to prevent the escape of substantial amounts of oxygen'in the effluent gas from the primary column, and, at the same time,

makes it necessary to exercise very. much "5 I greater care in the operation of the primary rectification in order to se'cure'a' constancy of composition of the oxygen product and to prevent very se'riouslosses of oxygen and argonfrom the top ofthe main rectification column. I t

All these difficulties, as T have described them, arising from the operation of the auxiliary column, "contribute to the low efficiency of recovery attained in the o per ati'on of the commercial method under consideratiou. The most serious cause, however, of the low efficiency is the fact that the attempt is made to separate in one op-' eration and in a single rectification column substantially allthe nitrogen contained in the air treated. It is impossible, however, to obtain at the top of the primary rectifi- -cati'on column substantially pure nitrogen and at the same time an oxygen-argon product of sufficiently low mtrogen content to be successfully treated in the auxiliary,

condenser and rectification column.

Furthermore. it has been found to be impossible to efiiciently produce oxygen of high purity, and, at the same time, argon of the'desired purity by the earlier method.

\ This result is doubtless due to the failure to balance all of the factors efi'ecting the operation, a result which has been achieved, however, in the method hereinafter described. In the operation of the method which forms the subject of the invention, onlya portion of the. gaseous mixture treated is liquefied andv the liquefaction is accomplished at the initial pressure, i. e.,,' as delivered by the compressor. Approximately 52% of the original air passes through the apparatus unliquefied and this fraction con sists of substantially pure nitrogen and is available at the original pressure. The ,major portion of the refrigerative effect necessary in the whole apparatus is derived from this high pressure nitrogen by ex-- panding it with external work in a suitable motor or engine after it has been brought into heat exchanging relation with, the in coming mixture. This expansion engine opcrates-continuously between the main compressor pressure and an exhaust pressure only enough greater than one atmosphere to cause the expanded nitrogen to flow throlfgh the subsequent liquefier and inter changers. The exhaustnitrogen is. conducted first through a liquefying compartment forming an extension of the backward return condenser at the base of the primary Y column and located at the lower end-of obtainable by the principle of backward return, inasmuch as no liquid unenriched in '-"oxygen is added to the liqu d derived-from aos rec the tubes of the backward return condenser, and it is also possible to obtainvthe maximum amount of high pressure nitrogen from the upper end of said condenser. The liquid obtained in the tubes of said condenser, aside from that produced by the engine exhaust passing through the liquefier just described,-is obtained as a result of the vaporization of liquids surrounding said tubes. For this purpose, two liquids are employed contained in separate compartments, one above the other. One of these is the 93-95% oxygen liquid which descends to the bottom of the main rectification column and collects around the tubes of the back- Ward return condenser, and the other is liquid returning from the auxiliary column as herenafter described. The primary rectification column receives at its upper, end the enriched oxygen liquid produced inside the tubes of the backward return? condenser after'its pressure has been reduced by an expansion valve located in the pipe through which it passes. The vapor leaving the tube of the column will have an oxygen content approximating that of the vapor having phase equilibrium with a liquid with an oxygen content of 45-46% and will thus approximate the composition of the original .unseparated mixture. This eflluent, after giving up its cold to the incoming mixture, is cycled back to the main compressor and thus re-enters the liquefaction cycle.

If air is treated, this effluent will be totally free from such substances as moisture and carbondioxide, which must be removed from atmospheric air previous to successful liquefaction and separation thereof at considerable trouble and. expense, and thus an important economy is accomplished compared with methods which reject in the waste gases the portion of air passing through the apparatus unseparated. The amount of unseparated air thus returning to the compressor is found tobe from 30 to 35% by volume of the air entering the compressor directly from the atmospherefa'nd this procedure thus totally avoids the serious losses of oxygen and argon in the effluent gases leaving the rectification column-which are experienced in hommercial methods as heretofore practiced. The 9395% oxygen liquid produced at the base of the primary rectification column passes through a pipe and pressure reducing valve and enters the auxiliary rectification column at an intermediate a level.

The operation of the auxiliary condenser and 'rectifieris similar to that in the commercial method described above, except for thereturn from theauxiliary to the primary rectification column of the liquid equivalent of that passing from the primary column to the auxiliary. This liquid equivalent, instead of being derived indirectly from. the

, v 1 a weaves excessliquid accumulating in the auxiliary column, is obtained directly and automatically from the auxiliary coluinn by placing thelatter at such a level with respect to the r'imar'y rectification column, that when the quid at the base of the auxiliary column reaches a predetermined level, it automatically overflows into a liquid pipe passing horizontally from the auxiliary column to the primary rectification column. This pipe enters a special compartment surrounding the tubes of the primary backward return condenser located between the liquefier com:

partment thereof already described and the compartment containing the 9349570 oxygen liquid. Sincethe liquid flowing through this pipe is derived from the base of the auxiliary column, it will be substantially pure oxygenand the pressure thereof will be somewhat lower than that of the liquid collecting at the bottom of the primary rectification column.- Tt-will thus readily evap- -orate by indirect contact with the ascending vapors inside the tubes of the primary condenser, and thus vaporization will be automatic, since only the excess liquid from the auxiliary column returns to the main column. The pipe carrying this liquid, since it passes directly from one column to-the other, can be made very short, and it will not be necessary to provide in it any regulating valve for controlling the flow through it.

The fiow of liquid therein, being automatic, will not require any attention from the operator, and the arrangement also avoids any heat leaka e due to the presence of a valve requiring irequent adjustment. The liquid oxygen evaporating in the special compartment of the primary backward return condenser as described constitutesthe oxygen product of the separation, and after being conducted back to heat exchanging relation with the incoming mixture, is led directly to a gasometer or a balloon,

The argon product is derived from the auxiliary compressor cyclein a manner similar to that employed in the commercal method already described. The only points in the cycle herein described at which argon can escape, other than at the proper outlet, is from the top of the primar 1 backward return condenser, i. e., with t e high pressure nitrogen or with the oxygen produced by the method.

' Therefrigerative efiect available in the method, as T have described it,- by reason of the relatively large quantities of high pressure nitrogen leaving the top of the main condenser, will be considerably in excess of that necessary to keep the cycle in operation. This excess of available energy may be utilized in various ways; for example, we may divert a portion of the engine exhaust for the purpose of precooling the atmospheric ialpplication of Claude C. Van Nuys,

ralityof partitions

6, 7, 8 and 9, into a lower rectifying compartment 10, a chamber 11 for cold gaseous products which circulate about the bafiies 12 therein, a liquid cham'ber 13,

0. 453,577, or external heat may be another chamber 14:, and an upper rectifying compartment 15; The purposesand ifunctions of these several compartments will more clearly appear asthe description pro ceeds.

Thegaseous mixture undergoing liquefaction is delivered through a pipe 161:0 the compartment 10 beneath a plurality of trays 17 therein, and proceeds upwardly through the trays in direct contact with liquid descending thereover, which liquid is enriched by contact with the gaseous mixture in the least volatile constituent of the mixture, while the most volatile constituent is separated therefrom and travels upwardly with the gaseous mixture. lates in the bottom'of the column and the gaseous mixture travels upwardly through tubes 18 in indirect contact first with cold gaseous products in the chamber 11, then with liquid in the chamber 13 and finally with liquid in the chamber 14 and recepta cle 19 disposed therein. The gaseous mixture thustraveling through the tubesis pro- The liquid accumugressively cooled and selectively liquefied,

that is to say, the least volatile constituent,

namely oxygen in case air is treated, to-- delivered to a head 20 in which the tubes 18 terminate. 'Thisresidual gas is delivered through ,a pipe 21 from the column at substantially the-initial pressure at which the gaseous mixture was introduced to the col-.

umn.

The liquid descending in the tubes 18 is delivered to the chamber 10 and passes over the trays 17 in contact with the gas entering through the pipe 16. The liquid is partially rectified and further enriched in the less v0 latile constituents, while the most volatile' constituent escapes therefrom and travelsupwardly with the gas into thetubes 18.

The liquid finally accumulates in the bottom of the column and is delivered through a pipe 22 havin a pressure-reducing valve 23 to the top of t e rectifying compartment 15.

" argon and oxygen, for example, escapes Tn this compartment, the liquid flows downwardly over-the trays 24 in direct contact with vapors arising from the liquid in the chamber 14, and receptacle 19 which is undergoing vaporization by heat interchange wit-h the gas in the tubes 18. Rectification of the liquid is thus carried on with gradual enrichment thereof in the less volatile constituen'ts, the most volatile constituent being transferred therefrom to the vapors arising through the trays. through a a pipe 25 to the receptacle 19 through which it overflows into the chamber 14, while the efliuent gaseous mixture, which in case air is being treated, contains nitrogen, oxygen and argon, is delivered from the column through a pipe 26.

As previously noted, the liquid accumulat-' ing in the chamber 14 consists of oxygen in case air is treated with a considerable proportion of the argon present in the atmosphere and some nitrogen, and it is desired to further separate these elements for'the purpose of recovering substantially pure oxygen and-a gas which is materially enriched inargon or which may be practically pure argon. For this purpose, it is necessary to subject the liquid to an auxiliary rectification, and, for this purpose, the liquid is led through a pipe 27 controlled by a valve 28 to an auxiliary column 29, which is divided by partitions 30, 31 and 32 into a chamber 33, acompartment 34 for the liquid product of the operation, a chamber 35 for the accumulation of liquid, and a rectifying compartment 36. The liquid from the pipe 27 is'wdelivered to trays 37 in the compartment 36 and flows downwardly thereover in direct contact with vapors from liquid which accumulates in the chambere35, thus causing enrichment of the liquid in the least volatile constituent, for example, oxygen; ,while nitrogen and argon for example, pass upwardly with the vapors throughthe trays. The efiuent mixture containing nitrogen,

through a pipe 38 and is delivered to an exchanger 39, where it gives up its cold to preceding portions of the same gaseous mixture after the latter has been compressed in a compressor 40 towhich the gas is delivered from the exchanger 39 through a pipe 41.

The compressed gas is returned to the ex-V changer through a pipe 42 and circulates about baiiies 43 therein and around the tubes 44 which carry the cold effluent mixture from the column 29. The compressed gaseous mixture thus cooled is delivered through a pipe45 to the chamber 33 at the bottom of the column 29 and passes thence upwardly through tubes 46 in indirect. contact with liquid in the compartment 34 and chamber 35. In the tubes, the gaseous mixture is liquefied partially under the principle of backward return, the liquid returning to The liquid is delivered weaves other vapors in the compartment through the pipe 26.

The liquid accumulating in the bottom of the column 29 is delivered through a pipe 50 having a pressure-reducing valve 51 to the top of the rectifying compartment 36 and flows downwardly over the trays 37 therein, eventually mixing with the liquid delivered to the auxiliary column through the pipe 27. It will be noted that the liquid delivered to the rectifying compartment through the pipe 50 has already passed through the column and has been subjected to recompression and liquefaction to separate further quantities of the most volatile constituent which escapes as the residual gas. This liquid will in the course of operation become substantially enriched in oxygen, while more and more argon accumulates in the gaseous efliuent from the auxiliary column which is recompressed and returned to the column. When enrichment in argon has reached the desired point, a portion of the gas may be withdrawn from time to time through a pipe 52, controlled by a valve 53, and delivered to a. gasometer 54 or other means of storing the gas. The substantially pure oxygen liquid is delivered through a siphon tube 55 from the chamber 35 to the compartment 34, where a portion of it is vaporized by heat interchange-with the gaseous mixture passing up through the tubes 46. Under certain conditions, this vapor may pass up through a-tube 56, the end of which is sealedunder the liquid in the chamber 35. V I It is desired, however, to return the major portion of the pure oxygen liquid accumulating in the compartment 34 to the pri mary column in order that the low temperature requisite to the operation of this column may be suitably maintained without resort to the expedient herein before 'referred to, of liquefying the incoming gaseous mixture in a coil disposed in the auxiliary column.. A pipe 57 is therefore provided to connect the compartment 34 with the chamber 13 in the primary column. The end of the pipe 57 is disposed near the bot tom of the compartment 34 so that the liquid forced over into the primary column when the predetermined level is reached in the auxiliarv column is oxygen of substantial purity,

which is one of the products of the opera- -tion. The liquid which is thus supplied to 'A by-pass 62 controlled by a valve 63 connects the chamber 14 of the column to the pipe 58, the valve 63 being closed in the normal operation of the apparatus but opened in starting the apparatus when the auxiliary column is inoperative, the valves 28, 59 and 61 being closed under these conditions, so that no liquid is'delivered to the auxiliary column and no products are withdrawn therefrom. I

- The several products delivered from the apparatus, that is to say, the residual gas in the pipe 21, the effluent mixture in the pipe 26, and the product delivered through the pipe 58 each leave the columns in relatively cold condition and it is essential to preserve this cold in order to efficiently maintain the desired operation.

A and B, each provided'with a plurality of

tubes

64 and 65 about which the incoming mixture compressed in a compressor 66 and conveyed to the section A through a pipe 67 is forced to circulate by baflies 68. The two sections of theexchanger are joined by a pipe 69 to which a purge or drain 70 controlled by a valve 71 isconnected.

The effluent gaseous mixture in the pipe 26 is delivered to a chamber 72 at the end of the section B of the exchanger and travels thence through tubes 65 to a chamber 7 3 at the opposite end of the section, thence through a pipe 74 to a chamber 75 at the end of'theisection A of the exchanger. In the section A, the gas travels through tubes 65 to a chamber 76 from which it is withdrawn through a pipe77 controlled by a valve 78 and delivered to an expansion engine 79 where the gas is expanded with external work. and thereby materially cooled. The cold expanded product is delivered by a pipe 80 toa chamber 81 at the end of the section A of the exchanger and thence passes through tubes 64 to a chamber 82 at the other end of the exchanger.

It will be recalled that this gaseous effluent contains in the case of the treatment of air, nitrogen, oxygen and some of the argon originally present in the aiftreated.

This material is dry and free from carboninlet 84 of the compressor 66 and mixes with the incomlng gaseous mixture such as air which is-constantly drawn into the compressor for treatment.

Consequently, {an ex-.

changer is provided, consisting of sections ,ing through the tubes 18.

The residual gas or nitrogen delivered from the primary column .through the pipe 21 enters a compartment 85 at one end of the section B of the exchanger and passes thence through tubes 64 to a compartment 86 at the opposite-end of the section, thereby giving up a portion of its cold to the incoming gaseous mixture. This residual gas amounts to more than substantially 50% by volume of the original mixture and is, under the conditions hereinbeforc specified, delivered at substantially the pressure to which the original mixture is subjected before it enters the primary column. Consequently, after being warmed in the section B of the exchanger, it is delivered from the chamber 86 to a pipe 87'controlled by a valve 88 to an expansion engine 89 where it is expanded and thereby cooled, the work thus developed being capa: ble of application for any suitable purposeas for example, compression of further quantities of the gaseous mixture in the system. The cold expanded residual gas is delivered through a pipe 90 to the chamber 11 of the primary column where it serves to cool and liquefy the gaseous mixture travel After passing about the baffles 12 in the chamber, the residual gas is delivered by apipe 91 to a chamber 92 at one end of the section B of the exchanger and travels through tubes 65 to a chamber 93 at the opposite end'of the section, thence through a pipe 94-to a chamber 95 at one end of the section A of the exchanger, thence through tubes 65 to achambeifl96 at the opposite ends of the section A of the exchanger through which it escapes through a pipe 97. The residual gas may be stored for any suitable purpose or discharged to the atmosphere.

The gaseous product, for example substanti ally pure oxygen, is delivered through the pipe 58 to a chamber 98 at one end of the section B of the exchanger and travels thence through tubes 65 to a chamber 99 at the opposite end of the section of the ex- I is stored for subsequent use.

From the foregoing, it will be noted that the features which have been hereinbeforepointed out as distinguishing the method which forms the subject matter of the pres- -ent invention from the prior art are necessarilyv employed in the apparatus asillustrated in the drawing and described herein. As a result of operation in the manner'des scribed, it is possible to produce and deliver from the apparatus substantially pure. oxygen, for example pure nitrogen and agaseous mixture principally consisting'of argon and oxygen, the argon approaching substantial purity. Furthermore, the operation is exceedingly economical because of the elimination of many of the defects which characterize methods heretofore employed,

and ofthe provision for the recovery of energy expended in compressing the original gaseous mlxture.

Obviously, although the invention is more particularly designed for the purpose of recovery ofnitrogen, oxygen and argon from the atmosphere, it may be employed in analyzing ternary gaseous mixtures, the con-' stituents of which have difi'erent boiling P0111135. When applied in the manner and for the purpose described, the method is readily controlled and requires much less at I the, constituents by" a primary liquefaction and rectification operation, thereby providing a liquid consisting substantially of the remaining constituents, separating the lat ter constituents by an auxiliary rectification operation, and returning one of the constituents in liquid form to assist in maintaining the necessary low temperature in the primary operation.

2. A method of analyzing ternary gaseous mixtures, which comprises separating one of the constituents by a primary liquefaction and rectification operation, thereby providing a liquid consisting substantially of the remaining constituents, separatin the latter constituents by an auxiliary rectification operation into a gaseous product enriched in one of the constituents and a liquid consisting of the other constituent in a substantially pure condition, withdrawing the gaseous product and returning the liquid to assist in maintaining the necessary low temperature in the primary operation.

3. A method of anaylzing ternary gaseous mixtures, which comprises separating one of the constituents by. a primary liquefaction and rectification operation, thereby provid ing a liquid consisting substantially of the remaining constituents, separating the latter constituents by an auxiliary rectification operation, including recomression and liquefaction of the gaseous cent from the auxiliary rectification and further rectification of the liquid formed, and returning the liquid product of the auxiliary rectification to assist'in; maintaining the necessary low temperature in the primary operation.

- aearee 4:- A method of analyzing ternary gaseous mlxtures, which comprises separating one of theconstituents by a primary liquefaction and rectification operation, thereby providing a liquid consisting substantially of the remaining constituents with a proportion of the first-mentioned constituent as impurity, separating the constituents of the liquid by an auxiliary rectification operation, including recompression and liquefaction of-the gaseous effluent from the auxiliary rectification with separation of the constituent constituting the impurity as a residual gas, and

further rectification of the liquid formed,

turning one of the constituents in liquid form to assist in maintaining the necessary low temperature in the pnlmary liquefaction operation.

6. A method of analyziiig ternary gaseous mixtures, which comprises separating one of the constitutents by a primary liquefac tion operation as a residual gas, subjecting the resulting liquid to a primary rectification operation to separate substantially the remainder of the first-mentioned constituent together with proportions of the other constituents in an efiluent gaseous mixture, thereby providing a liquid consisting substantially of the remaining constituents, separating the latter constituents by an auxiliary rectification operation, returning one of the constituents in liquid form to assist in maintaining the necessary low temperature in the primary liquefaction operation, and returning the efiluent mixture for further separation.

7. A method of analyzing ternary gaseous mixtures, which comprises producing therefrom, by a primary liquefaction and rectification operation, a liquid consisting principally of the least volatile constituent, subjecting the liquid to an auxiliary rectification, recompressing .and reliquefying the the gaseous e fiuelit from this rectification, utilizing the liquid in the auxiliary rectification, and returning the liquid product of this rectification to assist in maintaining the necessary: low temperature .in the primary operation.

8.: A method of analyzing ternary gaseous liquid, by a primary liquefaction and rect1- fication operation,

itile constituent with proportions of the otner constituents, subjecting this liquid to tification; thereby producing a liquid i 1 in the least volatile constituent and 'a JRSEOUS fraction, compressing this gaseous fraction, cooling it to separate a residual gas consisting of the most volatile constituent and a liquid containing chiefly two of constituents, returning. this liquid for further rectification, and withdrawing the li aid product of the rectification and utilizing it in producing the first-named liquid containing the least volatile constituent by selective liquefaction of the gaseous m1x-.

' ture.

ii). methodof analyzin ternary gaseous mixtures, which comprises producing by a primary liquefaction and rectification operation a liquid rich in the least volatile constituent and containing other constitu-v ents, suo ecting this liquid to an auxiliary rectincation, returning the liquid product of this rectificatioh to the priinary operar'ien tion and subjecting the efduent from the augiliary rectificatlon to recompression and reiiquefaction and further rectification. 31. A method of analyzing ternary gaseous mixtures, which comprises producing primary liquefaction operation a liquid 5 the least volatile constituentand conining a proportion of the remaining con-- rents, subjecting this liquid to continuing s rectification with recompression and refrig- --,.ration of the gaseous efiuent to separate liquid consisting substantially of the least -volatile const tuent and a residual gaseous product containing anotherconstituent, the

, gaseous efiuent being thereby progressively enriched in a third constituent, and return ing the liquid product of the auxiliary operation to the primary operation.

12. A method of analyzing ternary gasusmixtures, which comprises cnsisting principally of the least volatile onst tuent w th a. proportion of the rer aining constituents, subjecting this liquid to a continuing rectification with recompres-' 'sion and refrigeration of the gaseous efiuent to separate a liquid containing one of said const tuents 'in substantial. purity and a income of the least withdrawingportions of the gaseous V I producing 7 primary liquefaction operation ahquid' residual gaseousproduct cont another constituent, the gaseous efiuent being thereby progressively enriched with a third constituent, withdrawing portions of the gaseous effluent when it is suificiently enriched,

and returning the liquid product of the auxiliary operation to the primary operation. v

13. A method of recovering argon, oxygen and nitrogen from the atmosphere,

which comprises producing a liquid by a primary liquefaction operation, which consists principally of oxygen with proportions of argon and nitrogen, the major portion of the nitrogen being removed in gaseous form during the operation, subjecting this liquid to an auxiliary rectification, thereby producing a liquid consisting of substantially pure voxygen and ing argon and nitrogen, and returning the liquid oxygen to the primary operation.v

14. A method of recovering argon, oxya gaseous fraction includ- -v gen and nitrogen from the atmosphere,

which comprises producing a liquid by a primary liquefaction operation 1 which consists principally of oxygen with propor tions of argon and nitrogen, the major portion of the nitrogen being removed in gas- I eous form during 'theoperation, subjecting this liquid to an auxiliary rectification, thereby producing a liquid consisting of substantially pure oxygen and a gaseous traction including argon and nitrogen, returning a portion of the liquid oxygen to the primary operation, compressing the gaseous fraction, subjecting it to indirect contact with the liquid oxygen, thereby liquefying a portion of the gaseous fraction, leaving a residual gaseous product, consisting principally ofnitrogen and a liqui fraction including argon, returning the liquid fraction for further rectification fpied ac-' tion when it is sufiiciently enriched in argon.

15. A method of recovering argon from air, which comprises producing a liquid containing oxygen, nitrogen and argon by a pri-,

mary liquefaction operation, subjecting theliquid to continuing rectificatiomcompressing the gaseous efiuent, cooling it to separate a liquid containing chiefly argon and oxygen and a residue containing practically allot the nitrogen, using the last named liquid in the rectification, and returning the liquid product of the rectification to the primary operation.

16 A method of recovering argon from I air, which comprises producing a liquidcontaining oxygen, argon and nitrogen hy a primary liquefaction operation, subjecting the liquid to continuing rectification, compressing the aseous efiuentt, cooling it to separate a liquid containing chiefly argon and oxygen and a residue containin i t stantially of the nitrogen,

Mid

eous mixtures, which comprises separating one of the constituents by a primary liquefaction operation, thereby producing a liquid consisting principally of the remaining constituents, expandingthe first mentioned constituent, utilizing the cold thus developed to assist in maintaining the necessary low temperature' in the primary operation by passing the expanded con stituent in indirect contact wit-h the gaseous mixture undergoing liquefaction, further separating the constituents of the liquid by rectification into a liquid product consisting of another constituent in substantially v pure condition and a gaseous fraction consisting principally of the third constituent, withdrawing the liquid product and utilizing it to selectively liquefy the gaseous mixture in the primary operation.

18. A method of analyzing ternary gaseous mixtures, which comprises separating one of the constituents by a primary liquefaction operation, thereby producing a liquid consisting principally of the remaining constituents, expanding the first mentioned constituent, utilizing the cold thus developed to assist in maintaining the necessary low temperature in the primary operation, further separating the constituents of the liquid by rectification into a liquid product consisting of another constituent in substantially pure condition and a gaseous fraction consisting principally of the third constituent, and returningthe liquid product to assist in maintaining the necessary low temperature in the primary operation.

19. A method of analyzingternary gaseous mixtures to recover the constituents thereof in substantial purity, which comprises separating one of the constituents as aresidual gas bya primary liquefaction operation with backward 'return of the liquid formed, rectifying the liquid in the primary operation to produce a liquid enriched in another constituent and an efliuent gaseous mixture, recompressing and returning the gaseous mixture for further liquefaction in the primary operation, subjecting the liquid produced in the primary operationto an auxiliary rectification to separate a liquid product consisting of the principal constituent thereof, and withdrawing a: gaseous product from the auxiliary rectification consisting principally of the third constituent.

20. A method of analyzing ternary gaseou's rmixtures to recover the constituents thereof in substantial purity, which com- -product consisting of the principal cone panacea enriched in another constituent and an effluentgaseous mixture, recompressing and returning the gaseous mixture for further liquefaction in the primary operation, subjecting theliquid produced in the primary operation to an auxiliary rectification with recompression and reliquefaction of the gaseous effluent and return thereof to the auxiliary rectification to separatea liquid stituent thereof and withdrawing a gaseous product from the auxiliary rectification consisting principally of the third constituent. 21 In an apparatus for analyzing ternary gaseous mixtures,the combination of primary and auxiliary rectification columns, means for conveying a liquid which is impoverished in one of the con x stituents of the mixture from the primary to the'auxil'iary rectifier, and -means for returning a liquid which consists of another constituent in "a substantially pure condition from. the auxiliary to the primary rectifier.

22. In an apparatus for analyzing ternary gaseous mixtures, the combination of primary and auxiliary rectification columns, including means for liquefying gases in each of the columns, means for conveying a liquid which is impoverished in one of the constituents of the mixture from the primary to the auxiliary rectifier,,and means for returning a liquid which consists of another constituent .in a substantially pure conditionfrom the auxiliary to the primary rectifier;

'23. In an apparatus for analyzing ternary gaseous-mixtures, the combination of primary and auxiliary rectification col:

umns, means associated with the primary column for selectively liquefying the mixture, means for withdrawing theresidual unliquefied constituent, means for conveying the liquid product of the primary column to the auxiliary column, means in the auxiliary column to separate the liquid int an effluent mixture and a liquid consisting 0 another constituent in a substantially lltl llti

pure condition, and means for returning the liquid product of the auxiliary column to the primary column. p

24. In an apparatus for analyzing ternary gaseous mixtures, the combination of primary and auxiliary rectification columns, means associated with the rimary column for selectively liquefying t e mixture, means for withdrawing the residual unliquefied constituent, means for conveying the liquid product of the primary column tothe auxiliary column, means in the primary and auxiliary rectification columns. means associated with the primary rectification for. selectively liquefying the mixture. means for withdrawing the residual unliquefied constituent, means for withdrawing an efiiuent mixture, recompress ng and returning it to the primary column, means for conveying the l1qu1 roduct of the primary column to the auxiliary column, means in theauxilia column to separate the liquid into an e uent mixture and a liquid consisting of another constituent in a substantially pure condition, and means for returning the liquid product of the auxiliary column to the primary column. I

26. In an apparatus for analyzing ternary gaseous mixtures, the combination of primary and auxiliary rectification col-- umns, means associated with the primary rectification for selectively liquefying the mixture; means for withdrawing the residual unliquefied constituent, means for withdrawing an efliuent mixture, recom pressing and returning it to the primary column, means for conveying the liquid product of the primary column to the auxiliary column. means in the auxilia column' to'separate the liquid into an e uent mixture and a liquid consisting of another constituent in a substantially pure condition, means associated with the auxiliary columnto recompress and hquei'y the eifiuent mixture produced therein. and means for returning the liquid product of the auxiliary column to the primary column.

27 A method of analyzing ternary gaseous mixtures. which comprises separating one of the constituents by a primary liquefaction and rectification operation, thereby providing a li uid consisting substantially of the remaining constituents, separating the latter constituents by an auxiliary-rectification operation, returning one of the constituentsin liquid form to assist in maintaining the necessary low temperature in the primary operation and evaporating the liquid returned by indirect contact with the gaseous mixture treated in the primary operation.

In testimony whereof I alfix my signature.

CLAUDE C. VAN NUYS.