US2664718A - Process of and apparatus for lowtemperature separation of air - Google Patents

Description

Jan. 5, 1954 P. K. RICE PROCESS OF AND APPARATUS FOR LOW-TEMPERATURE SEPARATION OF AIR 3 Sheets-Sheet 1 Filed Oct. 11, 1949 INVENTOR PHILIP K. RICE TTORNEY Jan. 5, 1954 P. K. RICE 1 3 PROCESS OF AND APPARATUS FOR LOW-TEMPERATURE SEPARATION OF AIR Filed Oct. 11, 1949 3 Sheets-Sheet 2 INVENTOR PHILIP K. R'ICE ATTORNEY 1954 P. K. RICE PROCESS OF AND APPARATUS FOR LOW-TEMPERATURE SEPARATION OF AIR 5 Sheets-Sheet 3 Filed Oct. 11, 1949 INVENTOR PHILIP K. RICE ATTORNEY Patented Jan. 5, 1954 PROCESS OF AND APPARATUS FOR LOW- TEMPERATURE SEPARATION OF AIR Philip K. Rice, Kenmore, N. Y., assignor, by

mesne assignments, to Union Carbide and Carbon Corporation, a corporation of New York Application October 11, 1949, Serial No. 120,788

19 Claims. 1

This invention relates to an improved process and apparatus for the low-temperature separation of air to produce oxygen and nitrogen products, and more particularly to improvements of such process and apparatus resulting in the simplification of, or elimination of, refrigerationproducing equipment, and a reduction of the time and cost of starting an air separation system.

In systems for the low-temperature rectification of air, especially those for producing large amounts of oxygen, removal of the water vapor and carbon dioxide is more economically efiected by refrigeration than by mechanical means, but removal of the impurities, and particularly carbon dioxide, by refrigeration, has necessitated the use of expensive heat exchangers provided in duplicate or regenerative heat exchangers with low initial pressures. If periodically reversed regenerators, as proposed by M. Franklin, for example, United States Patent No. 1,970,299, are employed, refrigeration requirements of the process necessitate an expansion with the production of external work and the gas which is expanded is most conveniently a portion of the air. Since partly-cooled air would contain carbon dioxide and thus interfere with the expansion process, it has been proposed to employ air that has been cooled to condensation temperature, freed of carbon dioxide, and reheated to the desired temperature, for the efficient expansion with external work. Such reheating employs large heat exchangers that are provided in duplicate because the air employed for the reheating contains carbon dioxide which is deposited on heat exchanger surfaces. The duplication permits thawing of a clogged heat exchanger without interruption of the operation. An example of such a system is shown and described in United States Patent No. 2,619,81c, issued December 2, 1952, to Philip K. Rice and Edward F. Yendall. Since such heat exchangers are a large item of equipment, the elimination of at least one of them is an important advantage.

sually in such systems it is more economical to provide equipment for producing refrigeration (e. g., expansion engine or turbine and heat exchan er) of a size and refrigeration-producing capacity large enough only for the desired steady rate of oxygen production. Therefore the start ing of such a system after a shut-down period requires a long initial period of nonproductive operation. The practice of installing extra refrigeration-producing capacity to shorten the starting period adds expensive nonproductive equipment.

Among the objects of the present invention are to provide improved process of and apparatus for the low-temperatureseparation of air which permits operation to continue during a period when part of the heat exchange and refrigeration-producing devices are shut down for elimination of accumulated carbon dioxide; and which supplements the refrigeration produced by the operating refrigeration-producing devices so that quick starting of the entire apparatus after a long period or shut down can be effected without the use of extra mechanical refrigeration capacity.

Customary air separation plants are efficiently operated only at a substantially constant and continuous production rate, but there are occasions where the complete oxygen output of a plant could economically supply a single large consumer, such as a steel mill, which however usually has a demand for oxygen that varies considerably at difierent times of the day. To provide such a plant, which is large enough to supply the peak demand, involves not only high envestment costs, but great inefiiciencies, if it is attempted to operate the plant at sub-normal rates; or if operated at a continuous full rate, there is a serious problem of disposal of excess oxygen. By the principles of thisinvention such problems are efliciently solved by providing a plant including a low temperature air separation apparatus which is large enough to supply only the normal constant oxygen demand, and also a store of liquid oxygen with means to vaporize portions thereof according to a variable demand in excess of the normal. The stored oxygen consumed during peak demand periods can be replenished during periods of sub-normal demand. Further according to the invention, the stored liquid oxygen can be economically shipped to the plant from a large central plant because it is then practical to entirely eliminate the expense of providing mechanical refrigeration-producing devices.

Further objects of the present invention are: to provide a process of and apparatus for 1owtemperature separation of air by which a normal steady oxygen demand is supplied by separation of air by low-temperature rectification and the excess demand peaks are supplied. by vaporization of stored liquid oxygen; to provid an air-sepa-. rating plant in which mechanical means to produce refrigeration may be eliminated, the refrigeration requirement being supplied by liquid oxygen; and to provide a simple apparatus by which the refrigeration of liquid oxygen which is vaporized to supply part of for gase ous oxygen is usefully employed {or the refrigeration requirement of low-temperature separation of enough air to provide the balance of the demand for gaseous oxygen.

These and other objects and advantages of the invention will become apparent from the following description and the accompanying drawings showing exemplary embodiments of apparatus for separating gas mixtures such as air, and in cluding improvements according to the invention. In the drawing;

Figs. 1, 2, and 3 are schematic views of an ex emplary air separating apparatus including mechanical refrigeration-producing means according to the invention, three embodiments of means to supply refrigeration from a stored body of liquid which in Fig. l is liquid oxygen, in Fig. 2 is liquid air, and in 3 is liquid nitrogen; and

Fig. 4 is a schematic view of an air separation plant without mechanical refrigeration-producing devices and, according to the invention, including means for supplying the refrigeration from a stored body of liquefiet gas such as liquid oxygen.

In the drawings, similar items of apparatus in the several figures are designated by the same reference characters.

Referring now to the drawings, and particularly to Fig. 1, a means for preparing air for rectification which is intended to be representative of means customarily employed for such purposes. includes at iii a compressor which prefer ably compresses the air to be separated to a presu e elo 5 p. s. 1. (pounds per square inch). Such air is cooled to substantially its condensation temperature by passage through alternately reversed pairs of regenerators H and til, the pair of regenerators ii being cooled by outfiowing nitrogen product and the regenerators i). being cooled outfiowing oxygen product. The air is conducted to the warm ends of the regenerators by a conduit 53 with branches i l and 55. The branches l l and i5 connect respectively to reversing valves l6 and ii at the warm ends respectively of regenerators H and I2. automatic valves l3 and it at the cold ends of the regenerators ii and. i2 discharge the cooled air, which has been freed of moisture and carbon dioxide in the regenerators, to branch conduits 2 and Bi connecting to conduit 22 that discharges the air into the lower part 01'. a scrubber separator 33. The scrubber separator 23 is a device for washing the incoming air with liquid to scrub out residual hydrocarbon iinpuri es and any particles of residual carbon dioxide. upper portion of the scrubber separator 23 eliminates entrained liquid particles and provides a clean vapor that is conducted by conduit 2:3 to the lower end of an air-separating rectifying column C.

The rectifying column C may be of customary construction, having a high pressure chamber 25 closed at its upper end by a condenser 2t. The condenser 25 operates in the customary manner to condense vapors rising in the chamber 25, producing reflux for the chamber, and also producing liquid nitrogen that is collected on a shelf 21 directly under part of the condenser 26. The liquid nitrogen from the shell? El is conducted by a conduit 28 to the upper end of a low-pressure rectifying chamber 22 which is mounted above the chamber 25 and has at its lower end a liquid oxygen collecting space 3% that surrounds the condenser 26. The rectifying chambers be Sets of Y The provided with customary gas and liquid contact rectifying trays 3 I.

In the scrubber 23 the scrubber i lects impurities flows into a cup :3 from it is discharged through a condui 3% pro 2. with an expansion valve The conduit 35 conducts the liquid to a set of filters 36 and the cleaned scrubber liquid is conducted from the filters through a conduit 3? to an inter ediate portion of the low-pressure rectif ng chamber 29. Liquid that collects in the low r part of the high-pressure rectifying chamber 25 is conducted by a conduit 38 controlled by expansion valve 39 to the conduit for delivery to the inter ediate part of the low-pressure chamber The nitrogen product of rectification leaves the chamber 555! through a conduit Gil which preferably delivers the cold gaseous efiluent to a heat e. nger surrounding a heat exchange coil i h is interposed in the conduit 28 for sub-cooling the nitrogen reflux so to avoid excessive vaporization when the reflux is expanded through an expansion valve 53 also interposed in the conduit 28. From heat exchanger ii a conduit conducts the eliiuent nitrogen to a heat exchange coil 5 located in the upper part of the scrubber separator 23, the purpose of the heat exchan e coil &5 being to liquefy sonic of the scrubbed to provide scrubber liquid. From coil a c duit ii; conducts the effluent nitrogen the reversing valve system it? at the cold end of the regenerators ii. The warmed nitrogen l ves the reversing valve system 55 at the warm end of the regenerators through a conduit The oxygen product of rectification which boils in the space Bil produces cold gaseous oxyge that is conducted by a conduit &8- controlled by a valve is? to a second heat of range cell 5 3 also in the upper part or" the scrubber charnbc' 23 and from coil a conduit El conducts the product oxygen to the reversing valve system i quid that colill at the cold end of the regenerate-rs it. The oxygen product is delivered from he warm end of the regenerators through a conduit 52 con trolled by the reversing valves ll.

means for producing the use must be employed. iTZiSEllJS s provided by an expansion turbine which err nds a portion of air from substan ally the c 29. For such expansion, air free of carbon die: is preferred to avoid dificulty, so that a porn 11 of the scrubbed air from the chamber 23 is em ployed. Such air, however is a ready at condensation temperature, and it must be warmer. to provide efficient production of refrigeration by expansion with external work.

Such warming is preferably effected by a portion of the incoming air in order to avoid loss of refrigeration. To this end there drawn from an intermediate part of .he regenerators through connections controlled by valves 55 an equivalent portion of air which is condu by a ccn duit 55 to the warm end of a heat exchanger passage From the cold end or the passage 5? a conduit 58 conducts the cooled with awn portion of air to the lower part of the chamber 23. For use as explained hereinafter. a by-pass 59 from conduit 53 to conduit is provided and valves 6d, 6%, and are interposed respectively in conduits 55, and The air to beexpanded is taken from chamber 23 through to the space 30.

*i-nto' the tank. v "a hi'gher level, as indicated in Fig. 1, aliquid assure 5 "a conduit- 53 that conducts it to the mold end or a heat exchange passage ts around the passage 57, and from ii the warm :endbf the heat exchange passage-tea conduit its conducts the) air to the inlet-of the expansion turbine 5 A conduit 66 conducts the expanded "air to *an intermediatepart of the chamber :29.

There is preferably provided a by pass t'l be tween conduit :63 n and conduit 65 controlled by a valve' tt. 65 with the heat exchangepassage 6t are-controlled by valves 7! and 12 respectively, and a valve Z3 isn interposed inthe-conduit .65. "valved connections Mans 15 are disposed "at the'ends of the heat exchange passage 57 "for use "when thawing the passage of accumulated carbon dioxide.

oi iriceonly one heat exchanger 5-7 is provided,

the turbine- 51i is shut down when theheat exchanger :5! is taken out of' servic'e for thawing.

Refrigeration for continuin'g the operation .is provided, according to Fig. 1, by supplying-liquid oxygen-totheoxygen boiler space 39. Such liquid cXyg'enn'iay-be stored-ma well-insulated storage tank silwhich is surroundedby an insulating jacket 8! providing one of the best insulations 'forthe pui poseior example, a space filled with powder arid-hi hl evacuatedor gas. The tank. dil may-belargeenoughto supply liquid for a period necessary to thaw out the heat exchanger 5?. Alternatively, the tanker may be irnuch larger for purposes to be described hereinafter.

The 'ox'ygenisfed frorntank eb through a conduit bz 'coritrolled by avalve S3 and connecting tothe oxygen boiler space 38. A pipe's i 'rnayalso "bepro'vide'd connectin the upper parts ofthe space til and the tank 80 for equalizing o1 pressures and transmission of vapors. from the: tank During-normal operation .the tank 83 may be gradually filled by drawing. liquid oxygen from the space 35 through a conduit 85 connecting tvith the tan k 3t. If the tank tt is mounted at the sarne level as thespace 3t, gravity flow could be relied upon for moving the liquid If the tank as is positioned :at

o'xygen'pu'mp :86 may be interposed in the conduit-85. Since'it' niay be desirable to add'liquid oxygento thetankftc from an outside source, a

supply connection sl may also be provided. 'Thetank 85) may alsobe provided witha suitable liquid level indicating device 88. All cold conduits i and apparatus are protected by heat insulation ac cording to the usual practice.

The apparatus of Figs. 2 and 3 is similarto that or 1 in respect to the elements desighated by the same reference characters, but diner in the provisions for producing thereirigby the condenser Q2 at a verysiow rate into the tank e {l and when the refrigerationeproducing da vice is shut downplicguid err is 'clrainedfrom the tank' t at a controlled rate through a conduit 98 to the conduit 95, the rate being controlled The connections oroonduitsi'ta and :a'conduit Hill controlled by a valve I88.

by a valve :BQinconduit $8. The boiler chamber-this interposed inthe gaseous product oxygen conduit 48, and for feeding liquid oxygen fromthespaceoc to the boiler 93 there is provided A gas phase connection liil between chambers 353 and 798 may also be provided.

InbEig. v3, a storage tank I02 is positioned to receive liquid nitrogen through a conduit I03 from thclower part 'of acondenser Hi l, the conduit I03 being controlled by a valve I135. The condenser 1041's dispose'd inlthe auxiliary oxygen boiler 83 similar to that of Fig. 2. The condenser I64 receivesnitrogenfrom the upper part of the main condenser through a connecting conduit I01. Liquid nitrogen produced by condenser Int in excess oi-the rate required for filling the tank I62 "during aiperiod of operation is conducted through a branchconduit H18 leading from conduit N33 to the transfer conduit 28, and for feeding liquid nitrogen into the rectification device when the expansion turbine is shut down a conduit I69 is connected from theibottom of the tank I02 and the transfer conduit 28.

Conduits Hi8 and [39 have control valves I08 and res interposed therein.

Thenormal operation of the system of Figs. 1,

:2, and.3 is believed clear from the above description. It" is pointed out, however, that during nor- "mal operation, withtthe expansion turbine 54 in operation, the amount of refrigeration produced by the turbine is to be slightly in excess of that required for operating a plant to produce the desired amount of oxygen product. The slight excess of refrigeration is provided so'that the liquid which is to beaccumulated in the storage tanks 89, -90, or-l92 can be withdrawnfrom the :systemat a slow rate. Thus in the case of Fig. 1 "the pump 86 operates to draw liquid oxygen ata very slow rate from the oxygen boiler space 3E! and deposits itx'in the tank 8i]. Then when the heatexchangerhl is to be cut out of service and. the-turbine M isto beshut down, operation of the plant' andwithdrawal from the system may continue by closing valves G9, 54, ii, and i2 and opening valve 62 to by-p-ass the withdrawn air directlyto-the-scrubber -23. Substantially all the scrubbed air then enters the lower column 25 through con'duit M. When it is desired to maintain the turbine at operating temperature, a small flow of scrubbed air may be passed from conduit 53 by conduit 6'! through the turbine to the upper'co-lumn, by cracking valves and it.

The heatexchangepassagecl is thawed by passing warm dry gas'through it by use of the valved connections 14 and 15.

To prevent the lowering of the liquid levels in therectifying column due to loss of refrigeration, liquid oxygen is drawn from the stored body in tank 8b as needed. Such liquid oxygen may be fed to the liquid oxygen collecting space 33 at the needed rate regulated by the valve es. As soon as "heat exchanger 5'! has been cleaned, it may be returned to service by opening valves to, t l, i i, 72,

13 and closing valves 62 and as. When the turbine b l is operating properly, the feeding of liquid oxygen to the'chamber 35 can be stopped by closingvalve 83 and replenishment of liquefied oxygen begun'byoperation of pump 86.

Ifthe complete plant is shut down for a period,

thestartingof the plant can be facilitated by passing liquid oxygen from tank as to the oxygen boiler 3b tosupblement the refrigeration pro- 'duced by t'he turbine at. After steady operation is attained the liquid oxygen store can be replen- 7 ished. Also, if desired, liquid oxygen can be shipped to the plant and filled into tank 88 through the connection 8'5.

In the embodiment of Fig. 2 the liquid air tank 99 is gradually filled during normal operation with valve 9? slightly opened, and when the refrigeration turbine is shut down, valve 9! may be closed and liquid fed to the system from the tank 9% by opening control valve 99 sufiiciently to regulate the feed at the required rate. Obviously the liquid air from tank iii] could be fed to the scrubber, or preferably, to the lower part of the high pressure chamber 25, from which it would be transferred with liquid from said chamber through conduit 38 to the low-pressure rectifying chamber 29.

The embodiment of Fig. 3 may be operated similarly, except that it is liquid nitrogen that is condensed and accumulated at a desired slow rate and then during periods of turbine shut down, is gradually fed to the upper part of the low-pressure rectifying column.

Referring now to the embodiment illustrated in Fig. 4:, it will be seen that the system lacks a specific mechanical refrigeration-producing device, and the low-temperature refrigeration needed for operation is obtained by the evaporation of liquid oxygen which may be shipped to the plant. Air is compressed in the compressor MB and passed to nitrogen regenerators i it through a conduit i It in cooperation with reversing valves i It and the cooled air is conducted from the regenerators through the medium of reversing valves 5 iii and a conduit E22 conducting it to the lower part of the scrubber chamber 523. From the top of the scrubber chamber E23 the air is conducted by conduit 52d to the lower part of the high-pressure rectifying chamber E25. The chamber i2 communicates with main condenser I 26 in the lower part Ltd of the low-pressure rectifying chamber are and from a shelf E21 at the upper part of chamber 525 the transfer conduit 23 conducts liquid nitrogen to the top of the column H28. The scrubber liquid from the overhow cup i2 3 in chamber 23 is conducted by conduit i3 2 and control valve i'd through filters E36 and through a conduit it"! to an intermediate part of the low-pressure column E29. A transfer conduit connection itil conducts liquid from the bottom of chamber 525 to the transfer conduit it! after throttling through a valve use. Eflluent nitrogen flows from the top of the rectifying column through conduit ideto a heat exchanger i i! in which is heat exchange coil l iii of the transfer conduit M8, and from heat exchanger Mi a conduit l t-t conducts the nitrogen to a heat exchange coil i i-'5 the upper part of the chamber E23, the nitrogen being then conducted from coil i iii through a conduit i l-5 to the regenerators Hi through the reversing valves H3. The eflluent nitrogen leaves the system through a conduit lei.

If it is desired to produce an oxygen product of, for example, not over 98% purity, a pair of oxygen regenerators could be used to recover the refrigeration of the product oxygen as, for example, shown in Figs. 1 to 3. However, if at least part of the oxygen demand is for high-purity oxygen such as 99.5% purity, the warming of the oxygen product is effected by indirect heat exchange, and to this end there is provided a series of heat exchangers comprising heat exchanger passages 55% provided in duplicate for receivin a portion of compressed air from conduit H3 through a conduit 559. From the cold end of the heat exchange passages a conduit i52 conducts the partly-cooled air to another pair of heat exchange passages l53 in which the air may be partially liquefied. The thus cooled and partially-liquefied air is conducted from the heat exchange passages I53 through a conduit 154 to a lower part of the scrubber chamber 523. The heat exchangers [58-453 are installed in duplicate so that one of a pair can be thawed out while the other is on stream so as not to interrupt operation. The product oxygen to be warmed is led by a conduit I55 to the cold end of heat exchange passages l5'i around passages E53 and from the warm end of passages 55'5 through a conduit I58 to the cold end of heat exchange passages i553 around passages I58. The warmed oxygen is then conducted by a conduit Hit! to the inlet of an oxygen compressor it! which delivers it through a conduit 62 to a pipe line 133 leading to oxygen-consuming devices such as various operations in a large steel mill requiring highpurity oxygen.

The refrigeration necessary for continuing operation of the plant thus far described is provided by liquid oxygen which is fed from a storage tank ilt disposed within highly erficient heat insulation I! i. If this tank is situated at a proper elevation with respect to the rectifying column, the force of gravity may be relied upon for draining liquid at a desired rate from the bottom of the storage tank ii through a conduit 5'52 to the oxygen boiling chamber 13!]. Alternatively the liquid oxygen in the tank l'lil may be stored there in under a pressure slightly higher than the pressure existing in the low-pressure rectifying chamber 28, in which case the oxygen feed may be forced by pressure difference to flow from the tank 76 to the chamber Hit. As another alter native, illustrated herein, a liquid oxygen pump H3 may be interposed in the conduit H2 so that the tank lit may be at a low level and operated under atmospheric pressure, the liquid feed being forced by the pump from the tank llii into the chamber E39. In any event, a control valve lid is interposed in the conduit H2. The tank iii! may be filled from time to time through a filling connection H5, and vapors produced by heat leak to the stored liquid may be transferred from the upper part of the tank llii through a conduit ilii to the suction side of the oxygen compressor iti.

When the pipe line demand is variable, the plant is economically constructed and operated to produce oxygen corresponding to the low constant demand rate, and for supplying the excess peaks of demand there is conveniently provided a vaporizer llii interposed in a conduit i 9 connected between the discharge side of a pump and the pipe line N53. The suction side of the pump 18% is connected by a valved conduit $8! with the bottom of the storage tank Hi If a quantity of lower-purity (for example, 35%) oxygen is also required, such purity oxygen can conveniently be provided and supplied to a pipe line I82 by admixing a portion of compressed air with a portion of the high-purity oxygen livered through the conduit Hit, the connections for such purpose being controlled by valves and I84 respectively.

In the operation of the plant it may be sirable to have the air supplied through the h at exchangers I50 and it at a slightly higher pres sure than that which is supplied through the regenerators Ill and therefore there may be interposed in the conduit 15! a booster compressor I85.

In the operation of the embodiment of Fig. 4, all the oxygen shipped to the plant in liquid form and periodically filled into the tank lid is used to furnish gaseous oxygen to the consumer pipelines. A larger amount of oxygen, however, can be produced by operation of the air separation plant than the amount or" oxygen produced by vaporizing the liquid oxygen fed to the chamber I from tank llfl. At the same time the refrigeration of the liquid oxygen fed to the chamber I is usefully employed. It is seen therefore that the system economically supplies a large amount of gaseous oxygen at or close to the place or" consumption while requiring the shipment of only moderate amounts of liquid oxygen from a distant liquid oxygen plant. The investment expense as well as the maintenance expense of a refrigeration turbine and large heat exchanger are likewise saved. The system is capable of supplying a variable demand with a low investment and operating expense.

It will be understood that changes in the details of the systems disclosed herein may be made without departing from the principles of the invention. A continuation-in-part of this application is application Serial No. 344,431, filed March 24, 1953.

What is claimed is:

1. In a process for the low-temperature separation of air by rectification in which air freed of moisture and carbon dioxide is at least partly liquefied and the gaseous and liquefied portions are rectified to separate oxygen and nitrogen products, which products are used to cool further portions of air, supplying the entire lowtemperature refrigeration requirement for such process which exceeds that regained from the warming of said oxygen and nitrogen rich products' during at least a substantial period of continuous operation by providing a body of liquid having a composition similar to one of the liquids involved in the air separation process; holding such body of liquid at low temperature and separate from the liquids present in the separation process; and, during said period of continuous operation, continuously feeding portions of said body of liquid to the rectification where the liquid composition is similar to that of the body of liquid, and at a rate sufficient to supply said entire low-temperature refrigeration requirement, the gas products resulting from the liquid fed to the rectification from said body supplementing said oxygen and nitrogen rich products in cooling further portions of air.

2. A process according to claim 1 in which said liquid comprises mainly liquid air.

3. A process according to claim 1 in which said liquid comprises mainly liquid oxygen.

4. A process according to claim 1 in which said liquid comprises mainly liquid nitrogen.

5. In a process for the low-temperature separation of air by rectification in which air freed of moisture and carbon dioxide is at least partly liquefied and the gaseous and liquefied portions are rectified to separate oxygen and nitrogen products, which products are used to cool further portions of air, the steps of providing a body of liquid made from air; holding said body or" liquid at low temperature and separate from the liquids involved in the rectification; stopping the inflow of air and the rectiiying operation for a desired shut-down period While conserving said body of liquid; and concurrently with the resumption of said operation after such shut-down period, utilizing the re- 10 frigeration of said stored liquid to facilitate the starting.

6. A process according to claim 5 in which said liquid comprises liquid air.

7. A process according to claim 5 in which said liquid comprises liquid oxygen.

8. A process according to claim 5 in which said liquid comprises liquid nitrogen.

9. In a process for the low-temperature separation of air by rectification in which air freed of moisture and carbon dioxide is at least partly liquefied and the gaseous and liquefied portions are rectified to separate oxygen and nitrogen products, which products are used to cool further portions or air, the steps of producing refrigeratlon required for the normal operation of the process by expansion with production of external work of a portion of the air; accumulating gradually a store of a liquid produced from air during such normal operation; stopping for a desired period the production of refri eration by external work; and during said stoppage, continuing the operation of air separation by utilizing the refrigeration of said stored liquid in lieu of that normally produced by the work expansion.

10. A process according to claim 9 in which said liquid comprises liquid air.

11. A process according to claim '9 in which said liquid comprises liquid oxygen.

12. A process according to claim 9 in which said liquid comprises liquid nitrogen.

13. In a process for separation of air by lowtemperature rectification in which a main stream of air under pressure is freed of moisture and carbon dioxide, cooled to condensation temperature, subjected to at least partial liquefaction and then rectified to produce oxygen and nitrogen-rich products, and in which a second stream of air freed of moisture and cooled to a higher temperature such that it contains carbon dioxide, is further cooled by heat exchange with a portion of the main stream whereby carbon dioxide is deposited during such heat exchange and in which said portion of the main stream after being warmed by the heat exchange is expanded with production of external work to produce refrigeration for the normal operation of the process, the steps of providing a body of liquid made from air and having a, composition equivalent to one of the liquids present in the rectification; discontinuing the said work expansion and the said heat exchange for a period of time sufiicient to remove deposited carbon dioxide by thawing while by-passing said portion or the main stream to the rectification; and during such period of time, supplying liquid from the body of liquid to the rectification at a zone of equivalent composition at a rate to compensate the lack of refrigeration during the suspension of Work expansion.

14. In a process for the low-temperature separation of air by rectification in which air freed of moisture and. carbon dioxide is at least partly hquefied and the gaseous and liquefied portions are rectified to separate oxygen and nitrogen products, which products are used to cool further portions of air, the steps of providing a storage body of liquid oxygen holding said body of liquid oxygen separate from the liquids involved in the rectification; during continuous rectifying operat1on, utilizing portions of said body of liquid oxygen to produce refrigeration for the rectification at a rate sufficient to provide the refrigeration requirements of the air separation in excess of 11 that regained by the cooling of the air by the products; and delivering the oxygen product of the air separation and the oxygen product corresponding to the liquid fed from said body to consuming means.

15. Apparatus for the low-temperature separation of air by rectification in a rectifying column having an oxygen-rich liquid reboiler, which apparatus includes means for partly liquefying the air fed to the column, means for expanding a portion of air with the production of external work, a heat exchanger for regulating the temperature of the portion of air to be expanded, and means for by-passing said heat exchanger and said expansion means; an insulated container for holding a liquid made from air; means for feeding liquid from said container to said column; and means for regulating said feed during a period when said heat exchanger and expansion means are by-passed.

16. Apparatus according to claim 15 in which said liquid is liquid air and said feeding means connects with an intermediat part of the rectifying column.

17. Apparatus according to claim 15 in which said liquid is oxygen and said feeding means connects with the oxygen-rich liquid reboiler.

18. Apparatus according to claim 15 in which said liquid is nitrogen and said feeding means connects with the upper end of said rectifying column.

19. Apparatus according to claim 15, which includes means for feeding a liquid made from the air in the system slowly into said container during operation of said expansion means.

PHILIP K. RICE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,521,138 Van Nuys Dec. 30, 1924 1,890,646 Frankl Dec. 13, 1932 2,105,214 De Baufre Jan. 11, 1938 2,180,715 Messer Nov. 21, 1939 2,217,467 Bonnaud Oct. 8, 1940 2,321,445 Yendall et a1 June 8, 1943

Claims (1)

1. IN A PROCESS FOR THE LOW-TEMPERATURE SEPARATION OF AIR BY RECTIFICATION IN WHICH AIR FREED OF MOISTURE AND CARBON DIOXIDE IS AT LEAST PARTLY LIQUEFIED AND THE GASEOUS AND LIQUEFIED PORTIONS ARE RECTIFIED TO SEPARATE OXYGEN AND NITROGEN PRODUCTS, WHICH PRODUCTS ARE USED TO COOL FURTHER PORTIONS OF AIR, SUPPLYING THE ENTIRE LOWTEMPERATURE REFIGERATION RREQUIREMENT FOR SUCH PROCESS WHICH EXCEEDS THAT REGAINED FROM THE WARMING OF SAID OXYGEN AND NITROGEN RICH PRODUCTS DURING AT LEAST A SUBSTANTIAL PERIOD OF CONTINUOUS OPERATION BY PROVIDING A BODY OF LIQUID HAVING A COMPOSITION SIMILAR TO ONE OF THE LIQUIDS INVOLVED IN THE AIR SEPARATION PROCESS; HOLDING SUCH BODY OF LIQUID AT LOW TEMPERATURE AND SEPARATE FROM THE LIQUIDS PRESENT IN THE SEPARATION PROCESS; AND, DURING SAID PERIOD OF CONTINUOUS OPERATION, CONTINUOUSLY FEEDING PORTIONS OF SAID BODY OF LIQUID TO THE RECTIFICATION WHERE THE LIQUID COMPOSITION IS SIMILAR TO THAT OF THE BODY OF LIQUID, AND AT A RATE SUFFICIENT TO SUPPLY SAID ENTIRE LOW-TEMPERATURE REFRIGERATION REQUIREMENT, THE GAS PRODUCTS RESULTING FROM THE LIQUID FED TO THE RECTIFICATION FROM SAID BODY SUPPLEMENTING SAID OXYGEN AND NITROGEN RICH PRODUCTS IN COOLING THE FURTHER PORTIONS OF AIR.

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