US2547177A

US2547177A - Process of and apparatus for separating ternary gas mixtures

Info

Publication number: US2547177A
Application number: US57846A
Authority: US
Inventors: Graham E Simpson
Original assignee: Linde Air Products Co
Current assignee: Linde Air Products Co
Priority date: 1948-11-02
Filing date: 1948-11-02
Publication date: 1951-04-03
Anticipated expiration: 1968-04-03

Description

Apnl 3, 1951 G. ESIMPSON 2,547,377

PROCESS OF AND APPARATUS FOR SEPARATING TERNARY GAS MIXTURES Filed Nov. 2, 1948 2 SheetsSheet l INVENTOR ATTRNEY GRAHAMESIMPSON- A rll 3, 1951 Y e. E. SIMPSON 5 9 PROCESS OF AND APPARATUS FOR SEPARATING TERNARY GAS MIXTURES Filed Nov. 2, 1948 2 Sheets-Sheet a OXYGEN Z 20 &q

NITROGEN INVENTOR GRAHAM E.S|.MPSON j 2 BY I. a

, Q J, I x I I TTORNEY Patented Apr. 3, 1951 PROCESS OF AND APPARATUS FOR SEPA- RATING TERNARYGAS MIXTURES Graham E. Simpson, White Plains, N. Y., assignor to The Linde Air Products Company, a corporation of Ohio Application November 2, 1948, Serial No. 57,846

11 Claims.

This invention relates to a process of and apparatus for separating ternary gas mixtures of relatively low boiling point into their constituents by low temperature rectification, and more particularly to the low temperature separation of air to provide oxygen, nitrogen, and argon prodnets, with the simultaneous elimination of certain undesirable higher boiling point impurities which occur in the original gas mixture or air in very small proportions.

As set forth in United States Patent No. 2,287,158 of E. F. Yendall, the residual carbon dioxide and hydrocarbon impurities in air may beremoved prior to low temperature rectification of air by scrubbing the air after it has been cooled to about its condensing temperature with a fraction of liquid air to entrain the impurities in the liquid air. The impurity-free air may be rectified, but the impurities must be removed from the liquid fraction. According to the aforementioned pat-ent, the impurity removal is effected by evaporating a major part of the impurity-containing liquid by heat exchange with a gaseous oxygen product to make liquid oxygen. The concentrated residue of the evaporation is withdrawn and discarded. Other methods of efiecting a heat exchange to evaporate and concentrate the impurity-charged scrubber liquid have been proposed, but in general such methods involve more or less loss of eiiiciency.

The recovery of an argon product when separating air by low temperature rectification has been accomplished by withdrawing vapor from a part of the final air rectification where the vapor has a substantial argon content, and then subjecting such withdrawn vapor to an auxiliary rectification. To provide reflux for such auxiliary rectification, various expedients have been proposed which generally incurred some losses resulting in increased power requirements.

It is a principal object of the present invention to provide an improved process of and apparatus for separating a ternary gas mixture such'as air with the simultaneous elimination of impurities having higher boiling points than those of the components separated. Other objects of this invention are to provide a process of and apparatus for separating air to recover oxygen and argon with the simultaneous elimination of impurities collected in a liquid fraction of the air to be separated, in which the refrigeration produced by evaporation of the impurity-containing air may be usefully employed for supplying a reflux liquidfor washing higher boiling components from an argon-rich vapor; and for integrating with the main rectification of air an auxiliary rectification of argon-containing vapors and a preliminary separation from air to be rectified of higher boiling impurities in an economical manner, and which provides a system that is substantially self-regulating, easy to operate, and relatively simple to construct. A further object of the invention is to provide a method of and apparatus for separation of air by low temperature rectification including the elimination of impurities from air by concentrating them in a liquefied fraction of air in which a major part of the impurities which are entrained in a solid state in such liquefied fraction may be removed by filtration and the remainder of the impurities subsequently removed by distillation so that the amount of impurity-containing residue to be discarded is reduced to an immaterial amount.

These and other objects and advantages of this invention will become apparent from the following description and the accompanyng drawing in which:

Fig. 1 is a diagrammatic elevational view of an v exemplary apparatus illustrating the principles of the invention; and i Fig. 2 is a similar view of an alternative system according to the invention for producing gaseous oxygen.

The present invention will be described in connection with the apparatus of Fig. 1 which is particularly suitable for the separation of air to obtain a liquid oxygen product free of higher boiling impurities and a product having a high content of argon. However, modifications Within the scope of the invention may be made as exemplified in Fig. 2 if it is desired to recover the oxygen product in gaseous instead of liquid state and/or simultaneously obtain nitrogen in a high state of purity. Also it is contemplated that the argon-enriched vapor may be subjected to an additional auxiliary rectification if it is desired to obtain argon product of very high purity.

Referring now to the drawing and particularly to Fig. 1; the apparatus for preparing a gas mixture or air for rectification may be any of several known forms, that schematically illustrated being particularly suitable when the oxygen product is to be taken away in liquid form. A multi-stage compressor I t compresses air to a relatively high pressure and such compressed air after being cooled in a water-cooled after-cooler H is passed through a conduit I2 to the inlet end of a compressed air passage l3 extending through a countercurrent heat exchanger M. In the heat exchanger I4 the compressed air is cooled sufiiciently to eliminate the moisture. Such moisture-removing heat exchangers are customarily provided in duplicate so that accumulated moisture can be removed from one of the heat exchangers while the other is in service. A trap !5 with a drain valve 55 may [be mounted at the lower end of the passage 33.

From the trap the compressed air flows through a conduit ll having a branch is conneoted to the inlet end of a compressed air passage l9; extending through a liquefying heat exchanger 28. The cold liquefied air formed in the heat exchange passage i9 is conducted through a conduit 2! to a scrubber-separator chamber 22. The scrubber-separator chamber may be similar to that disclosed in the aforesaid United States Patent No. 2,287,158 and, as shown, comprises a chamber 22 within which are 'so'me perforated plates 23 or other means for efiecting intimate mixing of gas and liquid. The-conduit 2! enters below the plates 23 and there is provided an overfiow cup 25 with its upper opening immediately above the upper plate The scrubbei separator 22 may also be provided with a drain 25, the valve of which generally remains closed during operation.

A branch 26 of the conduit ll conducts a substantial proportion of the compressed air to the inlet of an expansion engine 2?. This engine expands the air passed therethrough with production of external work so that the expanded air has a temperature substantially correspond ing to its condensing temperature at the pressure existing in the scrubber-separator, which is pref erably about the same as the pressure of the first stage of rectification. This is of the order of 70 p. s. 1. gauge. The expanded air is led by a conduit'28 from the expansion engine to the lower part of the scrubber-separator 2'2. Interposed in the-conduit 25 is an expansion valve 2| through which the liquefied portion of the compressed air is throttle expanded to the pressure of the scrubher-separator. The scrubber-separator 22 is preferably constructed with sufiicient space above the gas and liquid contact means so that no drops of liquid are entrained "in the vapor at the top of the scrubber-separaton The vapor, free of higher boiling point impurities, passes through a conduit 29 from the toner the scrubbenseparator to the high-pr ssure stage'or lower column 351 or a two-stage air rectifying apparatus.

This air rectifying apparatus, except as explained hereafter, is generally of customary construction. The lower column or high-pressure stage chamber 36 is closed at its upper end by a tube sheet 3! to which are connected the tubes of a condenser 32. The chamber 30 may contain customary columntrays 33 such as perforated plates which eliect intimate contact with vapors rising in the column and reflux liquid flowing down the column. 'Under the tube sheet 3i there is an annular shelf 34 for collecting liquid condensed by the outer tubes of the condenser 32. Such liquid that collects on the shell 84 is substantially pure nitrogen.

The upper column or low-pressure rectifying chamber 35 extends above the tube sheet 35 and is formed at the lower end to provide a chamber 36 about the condenser 32 for effecting the boiling or liquid oxygen therein to produce vapors for the rectifying action in the upper column 35. The oxygen boils at the low pressure of the upper column at a temperature which is lower than the condensing temperature or" nitrogen in the condenser 32 under the pressure of the lower through the condenser column. The nitrogen collected on the shelf 34 is transferred through a conduit 35 provided with an expansion valve 34" to the upper end of the upper column This supplies reflux for the upper part of the upper column which is provided with the customary trays .31. Liquid that collects at the bottom of the lower column chamber 36 and which is richer in oxygen than air, is transferred by a conduit 38 controlled by an expansion valve 35' to an intermediate point of the upper column 35.

The nitrogen product of rectification leaves the upper column through a conduit 3% connected to the colder end of the heat exchanger 28 from which a conduit id conducts the eilluent nitrogen to the cold end of heat exchanger E4. The nitrogen escapes from the heat exchanger it through an outlet ll at substantially atmospheric temperature.

-When the upper column is in regular operation and the liquid oxygen withdrawal at a valved outlet 52 from the chamber 36 is at a rate suchthat high-purity oxygen is produced, it is found thata substantial ratio of the argon oi the original air is contained in the vapors at an intermediate point of the upper column. At-such intermediate point a vapor outlet conduit 43 isconnected to conduct the argon-containing vapor into the lower part of an auxiliary rectifying column 44. This column may also contain gas and liquid contact means such as trays Q5. The argon-containing vapor passes upwardly through .the column M- in which it is washed with a'refluxliquid produced by a condenser 46 at the top of the column M. The vapors on passing through thetubes of condenser 46 are subjected to partial liquefaction, the liquid produced being rich in argon and forming a suitable reflux for the auxiliary column 33. The argon-rich vapor which is not condensed passes through the condenser 5-6 and is withdrawn through a conduit'fil provided with a'control valve it. The liquid which eventually reaches the bottom of the columnid is substantiallystripped of its argoncontent and is mainly oxygen, and this liquid is preferably drained by a conduit ig into the upper column'35 at a point below the Vapor-conduit The liquid that overflows :into the cup :24 is withdrawn through a conduit d9 that conducts it to a filter Preferably there is provided an expansion valve ts interposed in the conduit 49 so that the scrubber liquid may be expanded to a lower pressure before it is-filtered and thereby its temperature-will be reduced. The filter 5B is diagrammatically illustrated and usually is one of duplicate set arranged so that one filter may be cleaned'while'another is in service. The filter is provided with a drain valve 5i for use when cleaning the filter. The filtered scrubber liquid is passed by a conduit :52 from the filterfiil to a chamber '53 surrounding the condenser lfi atthe top of the auxiliary column. This scrubber liquid, due to the iact that it contains a 'large proportion of nitrogen, boils at a lower temperature than thecondensing temperature of oxygen and therefore heat exchange readilyoccurs-to eiiectpartial condensation of the vapors passing The vaporized portion of the scrubberliquid passes throughaiconduit 5 5 into the upper column T35 soithat these vapors which are now free of higher boilingximpurities, may also be rectified. The.conduit '54 may also be provided vwitha regulatingvalve: 5.

Since a large partiof the higher boiling ;impurities will be removed by the filter 50 and only "a small amount will pass into the chamber 53,

most of the scrubber liquid that enters the chamber 53 may be vaporized and passed into the upper column 35, and there will be only a very slow increase in the concentration of higher boiling point impurities in the liquid being evaporated in chamber 53. In order that such concentrate may be removed, preferably at infrequent intervals, a drain valve 55 is provided, connected to a lower part of the chamber 53.

It is believed that the operation of the apparatus is clear from the above description. It will be seen that the withdrawal of a vapor containing the constituent of intermediate volatility (for example, argon), washing down a major part i of the higher'boiling component (oxygen) from the withdrawn vapor and returning such liquid to the main rectification, makes it possible to obtain the higher boiling component from the chamber 36 in a high state of purity, the lower boiling component from the top of the main rectification in a high state of purity, and to recover a concentrate of the intermediate boiling component which, if desired, can be further purified or subjected to another rectification to eliminate residual low boiling component.

The undesired or dangerous impurities are effectively eliminated by concentrating them in a liquid from which they can be removed before they enter the rectification zones. In air separation the impurities are concentrated in a liquid of high nitrogen content. By filtering the main bulk of impurities from the scrubber liquid, a concentration of the very small remainder that may pass the filter in dissolved state may be effected by evaporation of practically all the filtered scrubber liquid and draining off only a very small residue without increasing the impurity concentration above dangerous limits. Effecting the vaporization of the scrubber liquid by heat exchange with vapor at the top of the auxiliar column provides eflicient recovery of the refrigeration in the scrubber liquid.

When oxygen is withdrawn at 42 in the liquid state to make liquid oxygen product as in Fig. 1,

the proportion of the air liquefied is correspondingly high so that an effective quantity of scrubber liquid is produced for both elficient scrubbing action and for refrigeration of the auxiliary column. If it is desired to make gaseous oxygen, the make oxygen could be withdrawn from the chamber 36 in either the liquid or gaseous states, as illustrated in Fig. 2. When the oxygen is withdrawn as liquid, it is heated countercur rently in the liquefying heat exchanger 20 by providing therethrough an oxygen passage 60 wherein the oxygen is vaporized to produce gaseous oxygen and the required amount of liquid air in passage l9. If the oxygen is Withdrawn from chamber 36 in gaseous state, the amount of liquid air entering the scrubber at 2! will be much smaller and it will be necessary to augment the scrubber liquid for efiicient refrigeration of the condenser 46 at the top of the auxiliary column 4.4. This can conveniently be accomplished by providing a valved by-pass connection 56 between the bottom of the chamber 30 and the conduit 52.

In the embodiment of Fig. 2, the features similar to those already described in connection with Fig. 1 are designated by the same reference numbers. As previously mentioned in connection with Fig. 2, the heat exchanger 20 is additionally provided with a passage 60 for outgoing oxygen. Similarly the heat exchanger [4 is provided with an outgoing oxygen passage 6| which has an outlet 62 for the warm gaseous oxygen product. A conduit 63 connects the warm end of passage 60 with the cold end of passage 6!. The inlet 64 to the passage 60 is provided with a connection 65 to the vapor space of the chamber 36 and a connection 66 to the liquid space of chamber 36. These connections are controlled by

valves

65 and 66 respectively.

With valve 65' closed, and valve 66' adjusted, the liquid oxygen make withdrawn from chamber 36 through connection 66 is vaporized in heat exchanger passage 60 to liquefy air in the heat exchanger passage [9. Obviously, due to the refrigeration thus recovered by such liquid oxygen 7 evaporation, the refrigeration produced by compression and expansion may be less than in the case of Fig.1. With valve 56 closed. and valve 65 adjusted, gaseous oxygen is drawn from the chamber 36 and warmed in the passages 60 and BI, and in such case the latent heat of vaporization of the make oxygen is supplied by the condenser 32 instead of by the air in heat exchanger passage [9 so that the scrubber liquid is augmented by liquidrfrom the base of the chamber 30.

Obviously, if desired, the refrigeration contained in the argon product may be recovered by passing it through special heat exchange passages which may be provided therefor through the heat exchangers 20 and M.

It will be seen that the systems described are efiicient in that refrigeration contained in the scrubber liquid is returned. The auxiliary column is substantially self -regulating and the argon production is very simply controlled by regulating the withdrawal at valve 47'. There is practically no interference between the adjustments for controlling the oxygen purity and recovery and those for the argon production and the removal of argon makes it easier to obtain high purity oxygen with good yield.

It is to be understood that changes in carrying out the above-described process and changes in the apparatus illustrated may be made without departing from'the principles of the invention.

What is claimed is:

1. Process for separating air by low temperature rectification to obtain oxygen, argon, and nitrogen products which comprises compressing, cooling, and drying air to eliminate substantially all the moisture therefrom; further cooling and partially liquefying such air; scrubbing the cooled gaseous portion of the air with the liquefied portion to provide an impurity-free gaseous fraction and an impurity-containing liquid fraction; rectifying said impurity-free gaseous fraction to form an oxygen product of desired purity and a cold gaseous nitrogen product; withdrawing from a zone of the main rectification where the argon content is high, a vapor comprising mainly oxygen and argon; subjecting such vapor to an auxiliary rectification by washing with a reflux liquid formed by partial liquefaction of vapor from said auxiliary rectification; producing said reflux by a heat exchange between vapor of said auxiliary rectification and said impurity-containing liquid fraction to substantially vaporize said fraction and form an impurity-containing concentrate; removing said concentrate; passing the impurityfree vapors from said vaporization to the main rectification; withdrawing an argon concentrate from said auxiliary rectification; and utilizing at least the nitrogen product for countercurrently cooling incoming air.

22- A process In se a atin a .aqcqr in c aim 1 whi 9 d s t 261 92 5199 sai -m in rect ficat on e used refl .l uidimm .sa da li y rect ficat on- A pro es tor eparati air acc rd n t claim l whichincludesthe step of subjecting the perature and a minor .part .is liquefied and intimately mixed with the major part; separating the major andminor parts .so that the impurities are containedsubs tantiallyallin the minor liquid I part; rectifying the impurity-free major .part'to form a product of the higher boilingcomponent of desired purity, a product comprising mainly the lowest boiling point component, anda vapor at an intermediate zone of the rectification including the intermediate boiling point component; withdrawing said /apor from the intermediate-zone and subjecting it to an auxiliaryrec- 'tification by washing'with areflux liquid formed by condensation of part of the vapor ofsaidauxiliary rectification, withdrawing anintermediate coiling point component productfrom saidpartial condensation; efiecting substantialilaporization of said minor liquid parthy heat exchange with said vapor of the auxiliary rectification to form said reflux liquid-andaccumulate a remainder .containing impurities; withdrawing such remainder to eliminate the impurities;-and passing the vapor ofsaid vaporization to the mainrectification.

A-process for separating a ternary'gas mixture-according to claim 4 which includes the step or" subjecting the minor liquid part to filtration for remov alof solidified impurities prior to said vaporization. H

6. A process ior separating a ternary gas mixture according to claim. dwhich includesthe step of returning to the mainre'ctific'ation .a liquid remainder of thelrefiux liquid employed in the auxiliary rectification.

'7. A processiorthe separation of a gasmixture of three.mainconiponents including also .a

.minoramount. of higher boiling no it impurities which comprises providing such a mixture in conditions or" pressure and temperature in which a major part ofthe mixture is ,at condensation temperature and a i n'iinor part is liquefiedand intimately mixed with the major part; separating the majorandminor parts so that the impurities are contained substantially all in the minor liquid p r su e n th mnu ity-f s major part to a main rectification in twostages, the products of a first stage being passed to a second stage and the second stage formingla .cr d ct th h- 'h nb il g compo en .o fdc- .oQI i Sation'of part of the luap'or or said" to filtration to :remove at least pa jderffto "eliminate .th' mpuu res,

iary rectnicatio'nl' "or such"mixture in conditions jofpressu temperature in which a 'majorrpa rt purity drain ,at a low part of the hole,

.cludes means for draining refiuxli ..bottom of the auxiliary ,columnll'to .sa1 cclumnl clu des a filter interpose d in said rneans to ingthe liquid fraction to theb'oiler';

sired purity, a product comprising mainly the lowest ,ho'il'ingjpoin'tlcomponentfjand a" apior' at tion hy washing with a boilingpointcempoiient H tial condensation i subjecting" said purities; then efie'cting'fsuhsgtantial v per;

or said minor liquid part bylh'eatiex 's'aid ilapor of the auxiliaryflfec'tific said reflux liquid .and accumulate a re ain containing impurities} withdr' 'ing s vaporof saiuvam p 8. A,process for separating a ter tui e according to claim .7 which inc or returning to the mai rectification remainder of .therefiux liquidjemployed 91 Apparatus for ,the separation of a ternary gas mixture containing impurities whiohfapr ratu'sfcornprises means for providing f asupply o the mixture is atcondensationtemperature andiafminor part is'liquefied and mixedi'with' the j means for separating such'supplyii toj 'an'fim- .purity-free vapor fraction ,and a liquidfraction containing the impurities; a, mainiectfy n .urnn'; means for passing theyap'pr fraction to the rectifying 'columnjior recti cation therein; an auxiliary rectifyin column having ref ujx assing vapor from an 1 ph a vord ns.te cia 11'. Apparatus according to claimjl which in- GRAHAM E, sturgeon.

.n FER NQES C ED The following references are .of record in the iile of. this patent:

UNITED STATES PATENTS

Claims

1. PROCESS FOR SEPARATING AIR BY LOW TEMPERATURE RECTIFICATION TO OBTAIN OXYGEN, ARGON, AND NITROGEN PRODUCTS WHICH COMPRISES COMPRESSING, COOLING, AND DRYING AIR TO ELIMINATE SUBSTANTIALLY ALL THE MOISTURE THEREFROM; FURTHER COOLING AND PARTIALLY LIQUEFYING SUCH AIR; SCRUBBING THE COOLED GASEOUS PORTION OF THE AIR WITH THE LIQUEFIED PORTION TO PROVIDE AN IMPURITY-FREE GASEOUS FRACTION AND AN IMPURITY-CONTAINING LIQUID FRACTION; RECTIFYING SAID IMPURITY-FREE GASEOUS FRACTION TO FORM AN OXYGEN PRODUCT OF DESIRED PURITY AND A COLD GASEOUS NITROGEN PRODUCT; WITHDRAWISNG FROM A ZONE OF THE MAIN RECTIFICATION WHERE THE ARGON CONTENT IS HIGH, A VAPOR COMPRISING MAINLY OXYGEN AND ARGON; SUBJECTING SUCH VAPOR TO AN AUXILIARY RECTIFICATION BY WASHING WITH A REFLUX LIQUID FORMED BY PARTIAL LIQUEFACTION OF VAPOR FROM SAID AUXILIARY RECTIFICATION; PRODUCING SAID REFLUX BY A HEAT EXCHANGE BETWEEN VAPOR OF SAID AUXILIARY RECTIFICATION AND SAID IMPURITY-CONTAINING LIQUID FRACTION TO SUBSTANTIALLY VAPORIZE SAID FRACTION AND FORM AN IMPURITY-CONTAINING CONCENTRATE; REMOVING SAID CONCENTRATE; PASSING THE IMPURITYFREE VAPORS FROM SAID VAPORIZATION TO THE MAIN RECTIFICATION; WITHDRAWING AN ARGON CONCENTRATE FROM SAID AUXILIARY RECTIFICATION; AND UTILIZING AT LEAST THE NITROGEN PRODUCT FOR COUNTERCURRENTLY COOLING INCOMING AIR.