Oct. -1, 1946. 1 c. c. ‘VAN NUYS 2,408,710 v PROCESS FOR SEPARATING THE CONSTITUENTS OF AIR Filed Dec. 17, 1943 Q \h . § v.5 v\\mES .3 Lil %\ . .%\% R% w6 Q. we w 4 w $3;w1. ¢ h.Rm?wohuk éb V Q‘V. .H.3&m, 0%8 m, w m“: , -H-M” km9 .wN . .$5 m w“, . Q‘ ‘ x. w>\.IY wM BY ATTORNEY; 2,408,710 Patented Oct. 1, 1946' ' 1 e ' ’ PRooEssFoa SEPARA'I‘ING THE - , , UENTS OFAIRf Claude Van Nuys, Greenwich, Conn, assignor Incorporated, New to Air ReductionCompany, _York, N. 'Y., a corporation of New York Application December 1'7, 1943, Serial No. 514,593 - slolaiins. >. This. invention relates t ‘ (01. 62-1755) the separation of at mosphericair'into its constituents by liquefac tion and recti?cation, and particularly to im provements'in the method and apparatus there »for. ' ' - . . . 7.1 . In commercial liquefaction methods of ‘sepa rating oxygen fromthe atmosphere as heretofore practised, the necessary refrigeration to attain .low; temperatures is obtained'by compression and subsequent expansion of the-air treated. This necessitates initial compression of the air to rela ' matically an apparatus suitable for the practice .of the invention. In accordance" with the present . invention, the air tobe separatedis notjutilized- to produce any refrigeration in the cycle. I employ instead a separate-mitrogen cycle which, acts as a heat transfer agent everywhere in the cyclerThe air need be compressed in accordance with my in ventiononly to pressuresnot substantially higher 10 than three atmospheres absolute. Usually a pres-‘ sure ‘of two atmospheres,v vorv suf?cient pressure 'tively high ‘pressure of the order of 15-20 atmos-. ~~pheres. Such compression can be attained ‘only in reciprocating compressors which require oil lu brication. The oxygen of the air under such pres sures and at the temperatures resulting from compression causes decomposition ‘of; the lubri cating oil and the introduction-to the, air stream of; substantial proportions of hydrocarbons in ad only to ensure movement of the gas through the apparatus‘is needed to accomplish theypurpose Such pressures are easily at vof the invention. types of blowers which require tainable in various no internal lubrication. Hence no lubricating oil and decomposition products thereof are mingled with the air which is eventuallyseparated to re cover oxyen therefrom. The-procedure as. here inafter described effectively increases the propor .. dition to any’ which may be present; The-use of " vspeciallubricating oils does not avoid this source atmosphere and thepurity of the product, of Since‘ contamination. the hydrocarbons are I not removed, from .e?ect is compressed, circulated andv expanded in tion of'oxygen which can be recovered from the the air stream by the usual treatment intended to separate moisture and carbon dioxide, they ‘tend to accumulate and eventually ,find. their way .to the compartment of the apparatus where‘ liq- ' uidoxygen accumulates. The presence of such material in contact with pure ‘oxygen, whether liquid ‘or gaseous, is undesirable. 'Hence very elaborate attempts have been‘ made ‘heretofore to eliminatethe hydrocarbons at some-point inter mediate compression of the air andthe' forma tion of liquid or vapor rich in oxygen in which the hydrocarbons might accumulate. Such attempts. ‘ involve operations which interfere with the 'ef? ~ciency ofv the "cycle and the» use of necessarily complicated equipment. ' Furthermore, these at tempts have‘ failed substantially to achieve the desired object." It is still possible for hydrocar Thenitrogen which affords the refrigerative such a way as to providestrf?cient cold so that theair can be lique?ed ati-lowpressure. ~_The nitrogen of the refrigeration cycledoes not, min gle .at_;any point with the air undergoing sepa ration. Hence the presence of vhydrocarbons in the nitrogencycle is notvinimical to the method and a?ords no possibility of accumulation of hy drocarbons inthe presence of oxygen or products rich in oxygen. , The nitrogen can be compressed lto vthe ‘ necessary pressureyfor example ,2500 pounds per square ‘inch. in starting,5 the appara tus, ‘and from-900x170 1,009 pounds per squareinch thereafter,~ in any available formThe of - quantity compressor. = of .OiLlubrication maybe used. . ».- nitrogen necessary for the refrigeration-cycle will , ' .depend'upon the size 1 of the apparatus but ,will nolrin any case exceed the quantity of airicon tained in the ‘air separation r The‘. procedure will be readily understood’ by reference 'to' the drawing,v in which 5' indicates a ,' liquids rich in oxygen are present. I Y' ' ‘ w _ having the usual trays 6 and ' t‘ is' the object of the present invention to pro 45 jrecti?cation, column The columniis provided. at its top I bubble vcaps 1. .. . ', a simple . vide "and. effectivev ‘methqd‘ cadences .with an outlet ‘8 through-‘which ‘ratus'wh'ereby the "presence‘of' hydrocarbons re- I in nitrogen escapes. Liquid oxygen accumulates sulting from decomposition of} oil in, the compres in the bottom ofthe column, and the‘: vaporsv rise bons derivedfrom theiubricating oilito accumu late at points'in-the ‘apparatus where'gases or ’ Cyc1e~ ' 1 > ' ' through the trays 6' and bubble caps sion of the air can'be eliminated and further ini 50' .therefrom‘ l in contact ‘with liquid ?owing downwardly over atmosphere ‘can bevobtainedt: trays-i . ‘ other ‘Objects and advantages of the'inrcn?ob "f the ; fire provide ‘this liquid; - as; '; previously Yeom will‘be apparent as it is better‘understood‘by rei i pressed " to, Lethe; , initial pressure; preferably jsnpt provementsinthe separation of oxygen fromjthe "erenceto the following speci?cationfand theiac 'com'panying drawingtwhich;illustrates ‘diagram- 1 " greater than threeatmospheresfabsolute in any 2,408,710 3 4 suitable apparatus such as a blower (not shown) is introduced through a pipe 9 into an exchanger vapor from the condenser l4 escapes through the pipe 41 to the lique?er 46. Hence the nitrogen circulates continuously, affording all of the nec essary refrigeration for the system. The nitro I 0 and travels about pipes H and I2 therein in heat exchange relation with cold products of the separation. The air thus cooled is delivered through a pipe l3 to the bottom of a backward return condenser. l4 having tubes‘ l5 and ba?leslB therein. The air ?ows upwardly through "the tubes, being subjected therein to backward re turn condensation by heat exchange with nitro gen liquid and vapors supplie'dthrough a pipe 1:1. The liquid from the condenser I4, which is .en riched in oxygen, is delivered by a pipe, I8 con trolled by a valve l9 to an intermediate level of” the column '5. The gaseous residue from the tubes l5 consist‘ ing principally of nitrogen i'sedelivered by apipe gen in the refrigeration cycle does not at any point mingle With the air undergoing separa tion or the products thereof. Nitrogen separated from the air is withdrawn, as is also the oxygen 10 product, independently of the refrigeration cycle. Since the nitrogen employed for refrigeration travelsxin an independent cycle, it is immaterial whether or not it may carry hydrocarbons. These hydrocarbons, if present, cannot mingle with the air‘ undergoing separation and thus arrive at a point in thesystem where oxygen or products rich in oxygen are present. Thus the liquid oxygen which-accumulates in the bottom of the column 5 is free from any contaminating hydrocarbons 2!! to a condenser 2| containing tubes 22 through which the residue flows in heat exchange relation with liquid nitrogen supplied through a pipe 23. 20 which might have been introduced owing to the necessity of employing'oil in the initial compres ‘The surplus liquid from the condenser 2!‘ over sion. of the air. The use of the bloiver'to com flows through the pipe IT. The residue is con press the air‘ obviates that possibility. densedby heat exchange with the liquid nitrogen The invention as described affords a practical and "is d‘el'ivered'by a pipe 24 controlled by a valve ‘25 vto the top- of the column 5 and affords the 25 and simple solution of a problem which has ex re?ux nitrogen liquid required to effectively sepa isted for many years in the commercial produc v'lf’h'e oxygen product may be withdrawn as a liq 'uid‘v th-rcugh a pipe 2? controlled by a valve 28 and delivered by a liquid pump 29 to a pipe 33 ‘which delivers it to the pipes i 2 of the exchanger procedure and ‘in the apparatus as described without departing from the invention or sacri?c ing the advantages thereof. l0” wherein the liquid is vaporized. The oxygen ‘product is withdrawn through a pipe 3|, and 1. The method of separating the constituents of" atmosphere air in a liquefaction apparatus by liquefaction and» recti?cation which comprises tion of‘v oxygen by ‘liquefaction and recti?cation. rate substantially all of theaoxygen from the air It also permits substantially total recovery of treated: the oxygen content of the air, since the nitrogen e?luent nitrogen from the column is de livered‘ by the pipe 8 to'the tubes H of the ex 30 re?ux which issupplied at the top of the column prevents the escapeof oxygen in'the e?iuent. changer l9 and is withdrawn through a pipe 26 Various changes may bev made in the details of to any suitable receptacle or to the atmosphere. ‘ ‘delivered to any suitable storage receptacle. Al ternat'ively, oxygen in the form of vapor may be withdrawn through a pipe 32 controlled by a valve 33 and. delivered ‘to the pipe 3%. Liquid oxygen may’be withdrawn throughv a pipe 34 controlled ' by‘awvalve 35 t‘o'purge the column of any impuri ties which-may accumulate therein. _ ,To afford-the necessary refrigeration for the system‘, nitrogen is compressed in a compressor 36 to a suitable pressure as hereinbefore de scribed and delivered ‘by a pipe 31 to a cooler 38'. Thence‘ the nitrogen is delivered by a pipe . 39 to‘ an ‘exchanger All and travels about tubes 41 "therein where it is further cooled by heat ex I claim: ' compressingin'itrogen toa relatively high pressure, liquefying the nitrogen, compressing the air to a pressure not‘ materially in excess of that required to overcome the resistance to travel of the air through the apparatus without abrupt change in pressure, subjecting the air to indirect heat ex change with the liquid nitrogen ‘to separate liq uiid fractions enriched respectively in oxygen, and nitrogen, and rectifying the two fractions to‘ recover substantially pure liquid oxygen. 2; The method of separating the constituents of: atmospheric air'in a liquefaction apparatus 'by ‘liquefaction and recti?cation which comprises change with cold nitrogen vapor returning in compressing nitrogen to a relatively high pres the cycle. _ The cold nitrogen is delivered by a pipe sure, liquefying the. nitrogen, compressing the 42-“to a coil‘idt which is immersed in the liquid oxygen accumulating in the bottom of the col air :to;a pressure notmateria'lly'in excess of that required to overcome the resistance to travel of the air through the apparatus without abrupt ‘ ' ' ‘The resulting heat exchange cools the change; in pressure, subjecting the air to back ward- .return condensation "with partial con v‘of the liquidto maintain the vapor which rises densation-thereof, ‘condensing the gaseousresidue 7‘ through-the column. The sub-cooled nitrogen is then? delivered through a pipe ‘44 to the tubes 60 from ‘the ‘backward'return?condensation by in direct heat exchange'wit'h, the liquid nitrogen to 45 of an exchanger ‘5'5 where it is lique?ed by separate liquid fractionsenriched respectively in Iheat‘exchange with cold nitrogen vapors enter oxygen and nitrogen, and rectifying. the two frac iin'g'the lique?er through a pipe 41. These vapors tions to recover‘ substantially pure1 liquid» oxygen escape 'throgh a, pipe 48 to the exchanger 46 and ' .3. The methodof separating ‘the constituents v‘aft-"er ‘passing’ through the‘ tubes M of the ex of atmospheric .air by liquefaction. and recti?ca changer, are delivered by a pipe 49 to the com pressor 3'6. ' tion. whichcomprises compressing the air toa relatively low pressure such that expansion from -"_'vI’hegliquid nitrogen from the lique?er '46 is de thatpressure will not produce refrigeration suffr livered through a ‘pipe 50‘ and throttle valve. 5| 70 cient to effect liquefaction; thereof, subjecting ‘to the pipe Y23 and thus to the condenser 2|, af the compressed air to coolingand liquefaction in fording the liquid nitrogen necessary to liquefy [two fractions enrichedrespectively in oxygenand thenitrogen reflux for the column .5 and also to ‘ nitrogen .by indirect heat..,excha-nge with the liq ,' e‘lrect theinitial backward. return condensation nitrogen and causes vaporization ‘of a portion of the air entering the system. The nitrogen 75 uid'nitrogen,rectifyingthe two fractions to re cover substantially pure-liquid oxygen and‘main 2,408,710 taining the refrigeration necessary for the op eration by compressing nitrogen to relatively high pressure and liquefying the nitrogen to sup ply continuously the liquid required to effect liquefaction of the air. 6 taining a separate nitrogen cycle including com pression of the nitrogen to a relatively high pressure and liquefaction of the nitrogen by heat exchange with cold nitrogen vapors, subjecting the air at low pressure to indirect heat ex change with the liquid nitrogen to separate two 4. The method of separating the constituents of atmospheric air by liquefaction and recti? cation which comprises compressing the air to a relatively low pressure suoch that expansion from that pressure will not produce refrigeration 10 ' sufficient to effect liquefaction thereof, subject ing the compressed air to cooling and liquefac tion in two fractions enriched respectively in oxygen and nitrogen by indirect heat exchange with the liquid nitrogen, rectifying the two frac 15 tions to recover substantially pure liquid oxygen and maintaining the refrigeration necessary for the operation by compressing nitrogen to rela tively high pressure and liquefying the nitrogen by heat exchange successively with the liquid 20 liquid fractions respectively enriched in oxygen and nitrogen and rectifying'the two fractions to recover substantially pure liquid oxygen. 7. The method of separating the constituents of atmospheric air which comprises compressing nitrogen to a relatively high pressure suf?cient to afford the necessary refrigeration to liquefy the nitrogen, liquefying the compressed nitrogen, compressing the air to a relatively low pressure, vaporizing the liquid nitrogen by backward re turn condensation of the air with partial con densation thereof, liquefying the gaseous residue from such backward return condensation to pro vide two liquid fractions enriched respectively in oxygen and nitrogen, and rectifying the two frac tions to recover substantially pure liquid oxygen. 8. The method of separating the constituents tinuously the liquid required to effect liquefac of atmospheric air which comprises compressing tion of the air. . ' nitrogen to a relatively high pressure sufficient 5. The method of separating the constituents of atmospheric air which comprises compressing 25 to afford the necessary refrigeration to liquefy the nitrogen, liquefying the compressed nitrogen, the air to a relatively low pressure without con compressing the air to a relatively low pressure, tamifiating the air with lubricating oil, main taining a separate nitrogen cycle including com vaporizing the liquid nitrogen by backward re pression of the nitrogen to a relatively high turn condensation of the air with partial con pressure and liquefaction of the nitrogen, sub 30 densation thereof, liquefying the gaseous resi ' to indirect heat due from such backward return condensation to exchange with the liquid nitrogen to separate provide two liquid fractions enriched respectively in oxygen and nitrogen, rectifying the two frac two liquid fractions respectively enriched in, tions to recover substantially pure liquid oxygen, oxygen and nitrogen, and rectifying the two frac oxygen and cold nitrogen vapors to supply con substantially pure liquid oxygen.‘ 6. The method of separating the constituents of atmospheric air which comprises compressing tions to recover the air to a relatively low pressure without con taminating the air with lubricating oil, main and recompressing the vapor produced by vapor izing the liquid nitrogen to maintain the cycle. CLAUDE C. VAN NUYS.