US2685174A

US2685174A - Method of and apparatus for the separation of gases

Info

Publication number: US2685174A
Application number: US230301A
Authority: US
Inventors: Samuel C Collins
Original assignee: Joy Manufacturing Co
Current assignee: Joy Manufacturing Co
Priority date: 1951-06-07
Filing date: 1951-06-07
Publication date: 1954-08-03
Anticipated expiration: 1971-08-03

Description

2 Sheets-Sheet i S. C. COLLINS.

METHOD OF AND APPARATUS FOR THE SEPARATION OF GASES Aug. 3, 1954 Filed Jun e 7, 1951 1954 s. c. COLLINS 2,685,174

METHOD OF AND APPARATUS FOR THE SEPARATION OF GASES Filed June 7, 1951 A 2 Sheets-Sheet 2 1 m 2 0 a ,w A w a a v Q N H x3 MN \Q n n :1 7 NW I *W NWT \Q 4 x \QW h air" Patented Aug. 3, 1954 METHOD OF AND APPARATUS FOR THE SEPARATION OF GASES Samuel 0. Collins, Watertown, Mass., assignor to Joy Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania Application June 7, 1951, Serial No. 230,301

17 Claims.

This. inventionxrelates to improvements in :methods of and means for treating gases. It will be described particularly in its application to. the production of. substantially pure oxygen from air, but it will be. understood that its. use

is not so limited.

Formany uses, oxygen of rather high. purity, as, for example, 99.5%, isneeded, and it is often needed at substantial pressure, and it is desirable that the so-called generatorthe apparatus -for separating oxygen from the other constituents of air-bemade 'as completely atomatic in its functioning as possible.

In my pending application, Serial No. 122,077, filed October 18, 1949, for Methods of and Means for Treating- Gases, and now abandoned, and

in application Serial No. 383,541, which is a division of Serial No. 122,077 and which wasfiled on October I, 1953, also for Methodsoi and Means for. Treating Gases, there is disclosed-an oxygen generator in which'the entering air stream, after the removal from it, in a reversing heat exchanger, of water vapor and carbon dioxide, is

divided, and a major portion is passed through an expansion engine on the way to acolumn, while a minor portion-on the order of 12% of the total-is passed through a boiler-condenser in counterflow. heat exchange relation with the :leavingliquid oxygen product, and'the pressures .of the air .andof the liquid oxygen are so determined that during normal operationsubstan- ,tially. the entire heat of vaporization of the liquid oxygen is subtracted from the air and there is a liquefaction of. the equivalent. quantity of the air; which is then, after a suitable pressurereduction, passed into the base of the column. In said application theentering air stream was described as at a pressure of on the order of 158 p". s. i. g. at its point of entry into the boilercondenser and at a temperature on the order of 115 K.-, and the liquid oxygen which is vaporized in the boiler-condenserby the air which it liquefies entersthe boiler-condenser at approximately 50 p. s. i. g. and at a temperature of on the order wouldoccur: (ax-there would be less liquid air produced inthe: boiler-condenser, and (b) there would be a loss of refrigeration as a portion of the leaving oxygen product passes out of the boilercondenser unvaporiz'ed and enters the reversing heat exchanger in the liquid state. 'These facts are taken advantage oi-in an invention of Win W. Paget which forms the subject matter of an application for Methods of and'Means for Treating Gases, Serial No. 230,042, filed June 5, 1951 and according to which a booster takes the vaporized and warmed oxygen product and compresses it and discharges-it against a constant back pressure and in'which the suction pressure variations of the booster reflect back to the evaporator-condenser and control the-quantity and purity of the oxygen product. Ihe present invention is intendedto maintain the desired purity of the oxygen product while preventing pressure variations inthe evaporator-condenser which are attended'by reductions in the'thermal efnciency of the latter.

A column can produce from a given stream of air a certain quantity of oxygen of a particular purity, and by properly controlling'the amount of product a control of purity is possible. Accordingly, by supplying a constant amount of air to a generator and removing a constant quantity of oxygen product, in each case, of course, in unit time, a close control of quality of the product can be effected.

A desirable mode of providing for the delivery of a constant quantity of gaseous oxygen at a somewhat elevated pressure is to superimpose on the generator of my application above mentioned, as explained in said'Paget application Serial No. 230,042, filed June 5,1951, a booster which takes the gaseous product at a pressure on the order of 50 p. s. i. g. andcompresses it, for example, to

a pressure on. the order of 200 p. s. i. g. and delivers it against a constantly maintained back pressure. If a uniform mass of gaseous oxygen per unit of time is produced, say at 50 p. s. i. g., and the booster capacity is so designed that it will at constant operating speed normally neither draw down the pressure at its intake nor permit it to build up, a maintenance of the requisite purity may be expected, with a properly designed generator, and-with a constant raw air supply rate.

As the present invention is concerned particularly with the maintenance of a preselected purity, and as a lowering of purity attends an increase in the quantity of product delivered, it is possible, by employing an increase in the pressure inthe intake line of the booster which follows the delivery'by the column of more oxygen product as a means to effect a reduction in the quantity, and an improvement in the quality, of the product to effect a very satisfactory control. This may be done by providing a connection between the intake line of the booster and the oxygen product space in the columnsingle or double, and under the control of a suitable pressure responsive pressure control valve, providing for the return of gaseous oxygen from the booster intake line into the column. The return of this relatively much warmer gaseous oxygen results in two things:

(c) There is an evaporation of an increased quantity of liquid oxygen per unit of time, and thereby the quantity of oxygen product per unit of time delivered by the generator to the booster is reduced. This, bearing in mind the relation between quantity of product and purity of product will be seen to result in an improved purity, and it may be noted that the delivery of less oxygen product per unit of time will enable the booster to reduce the pressure at its intake, and thus reduce and ultimately interrupt the return of gaseous oxygen to the column.

(b) There will be also an increased rate of gas flow up the column, and this will result in a direct improvement in the purity of the liquid attaining to the liquid oxygen space in the column.

Since improved purity can be obtained by mere 1y partially closing a valve in the oxygen product line, and since the procedure above mentioned reduces the quantity of oxygen produced and also directly improves its purity, and since it is automatically rendered inoperative as it cures the condition which makes it operative, it will be evident that it constitutes a very useful and efiective control,

It is not necessary to rely on the use of a pressure responsive valve controlled by the suction pressure in the booster intake to control the return of gaseous oxygen to the column, but instead, if desired, a control responsive to variations in the mass flow in that line can be employed. For example, a venturi can be arranged in that line ahead of the intake surge tank, with taps at its throat and just ahead of the venturi, and a line connected with the suction line at a suitable point may be led back to the liquid oxygen space of the column and provided with a control valve governed by a bellows, diaphragm, or the like subjected to the pressures ahead of the venturi and in the throat thereof in such manner that increases in mass flow open the valve progressively and decreases in mass fiow result in its progressive closing. Obviously such a valve could be fully closed at normal uniform mass how, or slightly open, but in any event would prevent the mass flow of oxygen product becoming great enough to cause the pressure backing up in the evaporator-condenser from reaching a value at which there would be an impairment of the thermodynamic efficiency of the evaporator-condenser.

Thus, it will be apparent that in its broader aspects the invention is not limited to the use of a pressure responsive device controlled by the suction pressure of the booster for regulating the return of warm gaseous oxygen (or other) product to the liquid oxygen (or other liquid product) space of the column.

Application Serial No. 122,077 and application Serial No. 383,541 may be said to disclose the benefits of a reversing heat exchanger for efiecting removal of water vapor and carbon dioxide from an entering air stream, the division of the 4 purified stream and the passage of a major portion of it through an expansion engine and of a minor portion of it through a boiler-condenser, the condensation of. the minor portion by heat exchange with leaving liquid oxygen product, the union of the two portions of the entering air shown and their fractionation in a column, and the raising of the pressure of the oxygen product in its liquid state to some desired pressure, and the saving of refrigeration by abstraction of the amount of heat necessary to vaporize the oxygen product at its elevated pressure from the minor portions of the entering air stream and the liquefaction of the latter in a boiler-condenser. To this system, with a booster taking the oxygen product in a gaseous state and at its elevated pressure and raising its pressure to a higher desired pressure and discharging it against a fixed back pressure-the booster synchronized with the compressor supplying air to the system and so proportioned or designed as just to take the quantity of oxygen product made available at desired purity under normal conditions, I add a pro vision for returning, preferably from the booster intake line, under the control of a pressure responsive valve set to open at a predetermined pressure shortly to be considered, or under the control of a valve governed by a mass flow responsive device associated with such intake line, gaseous oxygen product to the oxygen product space in the column, to effect a reduction in the rate of oxygen product production, when it increases above the designed rate and suffers a deterioration in purity, and a resultant increase in its purity.

With this system, it is desired that there shall be no loss of thermodynamic advantage at the evaporator-condenser and that the complete vaporization of the oxygen product therein shall be continuously maintained, and therefore there will be a setting of the control device associated with the return line between the intake to the booster and the oxygen space of the column so that it will permit flow at a pressure at least slightly lower than that required for complete vaporization of the normal quantity of oxygen product in the evaporator-condenser. This, it will be observed, will mean that the booster will be designed to handle the normal production of oxygen of desired purity at a pressure slightly lower than 5-0 p. s. i. g., and will have the pressure in its suction line commence to build up, and effect the needed corrective control, before the pressure reaches p. s. i. g.

From the foregoing discussion, which will provide a preliminary understanding of the invention which will be advantageous in enteringupon a perusal of the detailed description of an illustrative embodiment of the invention from its apparatus aspects, it will be understood that the primary objects of the invention are to provide an improved apparatus for the rectification of gaseous mixtures, and an improved method therefor, and, incidentally thereto, to provide improvements in and new combinations of apparatus for the purposes mentioned.

It will be evident that the invention can be practiced from both of its aspects alike with single and double column apparatus, and a single column embodiment will be described in some detail, and a double column one just sufficiently to point out such difierences as are involved.

In the accompanying drawings, in which single and double column generator systems are shown aesmm a Fig. l'iszafdiagrammatic'view of an-oxygen generating and supplying apparatus utilizin a single column.

'Fig; 2 is. asimilar view of an apparatus utilizingfilldOllblE' column.

Fig. 315 a fragmentary detail showing amodification.

Reference may first be made to the system shown in Fig. l ofthevdrawings in which raw air, .at a temperature'of approximately 300 K., and

a pressure of on'theorder of 160 p. s. i. (allpresparatusmay be discharged to the atmosphere "through a-mufiler l. The valve mechanism 6 is -of the mechanically actuated type and is periodically reversed-every three minutes or so-in its position by-power, and in the position shown in Fig. 1, connects the deliveryconduit for entering air with a-conduit and eflluent (nitrogen) discharge with a conduit l2.

A reversing valve mechanism, suitable for the performance of the function of the valvemechanism 6 is illustrated .in the application of'Walter 'Mizen, Serial No.

190,745, filed October 18, 1950, now Patent No. 2,638,926, granted May 19,- 1953, but'it will be understood thatany other suitable valvemechanism may be utilized, as, *for example, the oneshown in my pending application, Serial No. 661,253, filed April 11, 1946; and still another suitable one. shown in the application of Win- W. Paget, SerialNo.'35,092, filed June 25, 1948, now Patent No. 2,638,923, granted May 19, 1953.

The compressor I has a crank shaft l3", having a fly wheel I 4 driven as by V-belts 5 by the drive pulley |6 of a suitable motor l1, and suitable reducing gearing not shown.. Reversals of the valve .mechanism 6 are, as above noted, adapted "to be efiected at relatively short intervals-on the order of three minutes. The conduits I and I2 are connected with difierent courses in thefirst of two heat exchangers 2| and 22. These-heat exchangers might be formed in one unit were it not desired to maintain-the overall height of the generator at a minimum. As will-shortlybe apparent, entering air passes through the exchangers 2| and 22in the order stated,-while leaving nitrogen efiiuent passes through them in the order 22 and 2|. Heat exchanger 2! is of the three-fluid type and includes coursesv 2|A, 2|B and HG. Exchanger 22 has a fourth course 22D later more fully mentioned, but also includes courses 22A, 22Band 220, corresponding generally to the courses 2|A, 2|B and 2|C, re-

spectively connected with the latter. The enterthe exchanger 22, and the course 2|Aof the exchanger 2|, the leaving oxygen product is discharged. The fourth course 22D ofexchanger -22 is used for the re-circulation through eX- changer 22 of a portion of'the entering air, the "better to efiect'the depositing out of impurities" with the course 21B. of. exchanger. 2|, and the r'COIldllit I2-Withscourse 2|C of exchanger 2|. The leaving oxygen :productpasses outwardly through course 2!A ofrexchanger 2|, andto a conduit 25, 'ofwhich more "will/be said at a later time. Course ZIC-of exchanger; 2|. is: connected by a conduit 3| withrcourse. 220 50f exchanger 22. Course 2|B of exchanger 2|.is. connected by a conduit '32. with course;:22B of .exchanger 22. A conduit 33. connects course 2|A of exchanger 2| with course 22A of'exchanger '22. It will be appreciated that entering raw. air: will flow alternately either through course 2 C, conduit 3| and :course 220, orcourse' 2|B; conduit 32 and course 223, while concurrentlynitrogen'efiiuent will flow outwardly through themes of the courses and passages last'mentioned not carrying-the entering air.

A suitable automatic" reversing: valve mechanism, generally designated, includes four auto- =matic-check' valves; 4|, 42, 43 and 44, and a suitable valve mechanism. is illustrated in my application,. Serial No. 661,253. *The lower end of course. 22B-has connected with it aconduit which leads to a'point' 'in thevalvemechanism 40 between the check valves 4| and 42. A conduit 41 connectscourse 22C withthe valve mechanism 4!} at a point between the: check valves 43 and 44. When the check valves 4| and 43 are open-'they are not open together-they permit flow to a conduit 50. The checkvalves 42 and 44 are separated from each'other by a septum 5|, and they open topermit-flow from a conduit 53 respectively .to the conduits .45: and 41. The conduit -leads to: an air cleaner orxfilter 54, the :further end of which,in terms of direction of flow ofentering air, is connected by a conduit 55 with the 'course" 22D, the fourth course in exchanger 22. @A suitable adjustable restrictor device 56 is arranged *at'thelower. end of the air cleaner f0! filter 54; att-he entrance-to a conduit 51, and creates a pressure difierence, perhaps on the order of two pounds, toicause a. desired quantity of air to be diverted through course 22D, the upper end ofzwhich'is connected by a conduit 58 with'the conduit 51 at point'59. An evaporatorcondenser .60; has a suitably insulated casing 6|, and includes an oxygen conducting course arrangement 62:and an air conducting course 63 in close heat exchange relation-with each other. The course 63 is connected by a conduit E l-with the conduit 51. The oxygen course 62 is connected by a conduit 65 with the bottom of course 22A of exchanger 22. Beyond point 5S,-a conduit :10 leads the air passing to it through the conduits .5! and-58 toan expansion engine l8.

When the air entering'the system is passing through course 22Biitflows past'the check valve 4|. When :course 223 is serving for outflow of nitrogen eiiluentfthe flow is from the conduit 53, past the check valve 42 and through conduit 45 :tocourse. 22B. When course 22C-is serving for theinflow ofair, the, entering -air flows past the .checl:yalve fiein transit between the conduit 47 rand the conduit 50. i f-hen course 22C being used to' conduct leaving nitrogen efiiuent, the "latter-flows from the-conduit 53, past the check -valve--44, and through the conduit 41' to course 22C. As the entering air is at a much higher pressure than the leaving nitrogen, the check valves 42 and M cannot be opened by the nitrogen pressure in conduit 53 while entering air is acting on their opposite sides.

A heat exchanger 23 has four courses numbered respectively 23A, 23B, 23C and 23D. Another heat exchanger 24 has three courses, 24A, 24B and 24C. The conduit 53 is connected with the course 23D, as here shown, with the top of the latter. The bottom of the course 23D is connected by a conduit 58 with the bottom of course 240, and the top of course 24C is connected by conduit H with the nitrogen eiiluent connection I2 of a single column I3.

The compressed air course 63 of evaporatorcondenser Ell communicates with the top of course 233 of exchanger 23 via a conduit I l. The bottom of course 23B is connected by conduit 75 with a pressure reducing valve device I6, which in the particular apparatus shown is adjusted to effect a pressure drop between its opposite sides of on the order of 88 p. s. i., when the compressor delivery pressure is 160 p. s. i. As will later appear, this is substantially the same reduction in pressure as occurs in the expansion engine It during normal oxygen production. The downstream side of the valve device 16 is connected with a conduit 1?, which leads to a boiler-condenser unit I8 in the lower end of the column 13. The course 23A of exchanger 23 is, as shown, connected at its top by a conduit IS with the oxygen course 62 of the evaporator-condenser 60, and the bottom of the course 23A i connected by conduit 80 with the bottom of the course 24A of exchanger 25. From the top of course 24A, a conduit 8| leads to a liquid oxygen pump LOP, later described. The unit Ii; is connected, at its other end from the conduit 'I'l, by a conduit 82, with the course 243 of exchanger 24, while the top of course 24B is connected with a conduit 83 whose other connection is later described. The remaining course 230, of exchanger 23, is connected at its top with an expanded air conduit 85, and its lower end is connected by a conduit 85 containing a check valve with a conduit 88, which leads to the conduit E7. The check valve 81 opens from the conduit 85 towards the conduit 83, when the pressure in the conduit 86 is suilicient to open the check valve 8? against the pressure in the conduit TI.

The expansion engine I8 includes a cylinder 98 admission and discharge valves respectively numbered 9! and 92. An engine of appropriate construction is illustrated in the Win W. Paget application, Serial No. 31,017, filed June 4, 1948, now Patent No. 2,678,028, granted May 11, 3.954, but it will be understood that other expansion engines may be used. Entering air flows past the admission valve 9%, when the latter is open, from the conduit lilto an in surge tank while the discharge valve 92, when open, perrni'ts the delivery of expanded air to a discharge surge tank 56, which is connected by a conduit 95 with an appropriately controlled valve mechanism 33, which when open permits the connection of the conduit 95 with a conduit Ell, opening into the column is somewhat below the top or the latter. When the valve 95 is closed, as it is during normal operation, the expanded air flows from the conduit 95 to the conduit 85 previously described. The valve 96 may be provided with any suitable control and a pressure fluid actuated control is diagrammatically indicated at 98. The expansion engine provides during normal oxygen production a pressure drop between its inlet and discharge of on the order of 88 p. s. i. (See the description above of the pressure reducing valve, and see also my copending application above mentioned, Serial No. 122,077.)

The liquid oxygen pump LOP is shown as mounted on top of the expansion engine cylinder and may be desirably actuated through the engagements of its piston operating rod Hill by the piston IGI of the expansion engine. The liquid oxygen pump may be suitably jacketed with colder fluid if desired, as in my application Serial No. 122.077, and is so shown in Fig. 1, in which a jacket chamber is indicated at I02.

The conduit 83 leads to a valve device H0, which is desirably adjusted to efiect a reduction on the order of 60 p. s. i., in the pressure of the fluid (liquid air) which flows through it; and the downstream side of the valve device is connected by a conduit III, serially, with the jacket I02 of the liquid oxygen pump and with the jacket I I2 of a strainer H3 for the oxygen product. The top of the jacket I I2 is connected by a conduit I I5, with the jacket H6 or" a super-cooler I I? for liquid oxygen passing to the liquid oxygen pump LOP. It will be noted that the conduit BI is connected with the discharge of the liquid oxygen pump LOP. Following the completion of its jacketing function, the liquid air passes from the jacket H6, through a conduit I to a device |2l through which liquid air may be admitted to the top of the column I3.

The column I3 may be of any suitable construction and is illustrated as of a conventional packed type. The liquid oxygen product passes to the strainer H3, through a conduit I whose lower end extends, at 128, into an open topped chamber I21 in the casing I28, whose upper and lower ends are connected as at I28 and I38 with the space outside the unit It in the bottom of the column I3. It will be evident that liquid oxygen will flow into the chamber I21 only when the liquid oxygen level in the column is at least slightly above the top of chamber I21, and that the liquid oxygen pump can draw liquid oxygen only when the level of the liquid oxygen stands in the chamber I21 high enough for the mouth of the conduit I25 to be submerged. It will, therefore, be evident that the liquid oxygen pump cannot aiTect the level of the liquid oxygen in the bottom of the column to the extent of drawing down this level below the top of the cham ber (21. From the strainer H3 a conduit 32 conducts the liquid oxygen to the intake of the liquid oxygen pump LOP.

During normal operation, about 12% of the total entering air stream is passed through evaporator-condenser 6t and is condensed by heat exchange with the leaving liquid oxygen stream. The liquid oxygen pump raises the pressure of the liquid oxygen to approximately p. s. i., and the pressure of the entering air stream in the course 63 of evaporator-condenser Bil is about 158 p. s. i., and it will be apparent that under these pressure conditions, the approximately 12% of entering air will be completely liquefied through giving up heat in the process of vaporizing the liquid oxygen in the course 52. It will be understood that if the pressure of the liquid oxygen should rise above 50 p. s. i. materially, it could not be wholly vaporized in evaporator-condenser BI), and some of it would pass over in liquid form into exchanger 22 where there would be a loss of refrigerating effect, and accordingly a smaller-quantity of liquid air would pass'into the column.

The conduit 25, through whichthe gaseous oxygen production at substantially 50 p..s. i. (its pressure is somewhat reduced by the resistance to flow in exchangers 2I and 22) is, as disclosed inthe application of Win W. Paget Ser. No. 230,042, filed June 5, l95l,-delivered to the intake surge chamber I5I of a booster I52, the piston I52P of which is driven with the air compressor I; and from the booster I52, the compressed gas eons oxygen is discharged to a discharge-surge chamber I53, and then the gaseous oxygen at a higher pressure, say 200 p. s. i., will pass through a conduit I 54 and through a heat exchanger I55, and through a conduit =I56, and to a predetermined back pressure maintaining valve I51, whose function it is to maintain the back pressure on the discharge of the booster at a constant 200 p. s. i. It will be evident thatother back pressures might be selected, appropriate alterations in the booster being made. All gaseous oxygen which passes the automatic back pressure valve is discharged to a conduit I58, and passes to a desired point of use or storage.

It will be evident that if a constant back pressure is maintained on the booster discharge line, conditions appropriate to uniform operation of the entire generating plant will subsist. It will be understood, however, that there are fortuitous variations in the operation ofa plant of this character, depending upon variations in the atmospheric pressure of the entering air, humidity, etc. Conditions may therefore develop which willresult in a temporary reduction in the amount of gaseous oxygen furnished to the intake of the booster I52, and if the booster intake pressure falls below a predetermined point, there might be an excessive number of compressions in the booster and there was therefore provided in-the Paget application Ser. No; 230,042, filed June 5, 1951, a by-pass connection E50, betweenthe lines 25* and I56. This by-pass connection, controlled by an automatic pressure responsive by-pass valve IE1, is responsive to pressure in the conduit 25, and opens, when that pressure drops to a predetermined point, to allow back flow of gaseous oxygen from the conduit I 55 to the intake to the booster I52, to preclude the compressing of gaseous oxygen through too great a range of compression, with resultant potential danger due to excessive heat of compression.

With the apparatus described, the compressor I, driven at a constant speed, delivers'a substantially constant mass per unit of time of air to the system. The liquid oxygen pump, LOP, withdraws all of the liquid oxygen produced in the column (its capacity is such that it actually normallydraws some vapor from the column)- and delivers it to the heat exchangers 24, 23,- the evaporator-condenser GI, and exchangers 22 and- 2I, and the oxygen product, then in vapor state, is delivered by the conduit 25 to the intake of the booster I52.

As' explained in said Paget application Ser. No. 230,042, filed June 5, 1951, if the pressure in thereforethe-purity atthe desired height) that the pressure inthe booster suction line will still be'well below the '50 p. s. i. level when corrective steps are initiated. In Fig. 1, I have shown a pressure responsive relief valve I55, responsive through a connection I 65, to the pressure in the conduit 25 and set to open when the pressure in that line is on the order of 45 p. s. i., and to deliver oxygen product, relatively warm and in a gaseous state, into the liquid oxygen space of the column through a conduit I57. This will immediately result in a reduction in the quantity of liquid oxygen produced per unit of time and in an assured'purity of the desired level. The capacity of the booster may very desirably be made such that it will handle the quantity of liquid'oxygen which is produced during some bleedback of gaseous oxygen to the column. In other words, some degree of bleedback may characterize normal operation;

From the'foregoing', it will be apparent that, in an oxygen generating apparatus which in cludes an evaporator-condenser through which a liquid owge'n pump forces, at an increased pressure, all of the liquid oxygen product and in which evaporator-condenser a quantity of air on the way to the column is liquefied by giving up enough heat to vaporize the liquid oxygen completely (a thing which requires that the liquid oxygen shall be at a pressure not exceeding a predetermined maximum since the counter-flowing air has its pressure predetermined bythe pressure of the air supply and by resistance to flow in heat exchangers in which water'vapor and CO2 are separated out), there is provided a booster working against a constant' discharge pressure and having its suction line connected with the conduit through which the gaseous oxygen product is discharged after being warmed to on the order of room temperature, which booster is made of such capacity that it will handle the normal volume of gaseous oxygen product produced per unit of time without having its suction pressure quite reach said above mentioned predetermined maximum pressure, and a by-pass, controlled by a pressure reducing valve responsive to pressure in the suction line of the booster, is provided to deliver to the liquid oxygen space of the column warmed gaseous oxygen in such volume as to improve the quality of the oxygen product through "the reduction in the mass of the product produced in the column, the setting of the by-pass controlling valve being slightly lower than said above mentioned predetermined maximum pressure, so that the latter pressure will not be reached in actual operation under any ordinary conditions. For example, if the evaporator-condenser will fully vaporize the liquid oxygen if the latter does not exceed 50 p. s. i., then the pressure responsive by-pass controlling valve may be set a few pounds lower, and supply warm gaseous oxygen to the column when the pressure in the suction line of the booster is 45 p. s. i., for example. Now, if the booster capacity is such as to handle the oxygen product at 45 p. s. i., that is, to handle the total normal oxygen production when the same-is built up to that pressure, vaporized and warmed, then the apparatus, in the event that an increased quantity, per unit of time, of oxygen product oflower purity is temporarily produced, will operate, through the resultant pressureincrease in the suction line of the booster,

to'by-pass a portion of the warm gaseous prodduct back-intothe column, with a resultant re-' duction in the quantity" of oxygen delivered per unit of time, an improved purity, and a return to a condition in which the booster can handle the total oxygen production with the suction pressure below that at which the by-pass valve will open. It will be understood, however, that it will perhaps be preferable so to predetermine the characteristics (including speed) of the booster that it will just handle the quantity of oxygen product at a pressure below the predetermined maximum above mentioned but above the setting of the pressure responsive by-pass control valve so that the booster will just handle the normal production of liquid oxygen, slightly boosted in purity and reduced in quantity by some feed back of oxygen product to the column.

Fig. 2 difiers from Fig. l in its disclosure only in essence in that a double column H3 is provided instead of a single column, and only those modifications which the employment of the double column necessitates need be pointed out. The column may of course be of many forms, but as illustrated has an upper, or low pressure, portion I'M, and a lower, or high pressure portion H5, and the construction of this illustrative column is shown and described in the copending application of Win W. Paget, Ser. No. 118,615, filed September 29, 1949 and now Patent No. 2,633,717, granted April '7, 1953. It will be observed that the liquid air is delivered into a shell I16 which is traversed by many conduits I77, which open through the side walls of the shell H6. The bottom of the shell 178 communicates with a chamber I13, and a portion of the enriched air which is condensed upon the outside of the conduits ill, after jacketing the liquid oxygen pump and the strainer through which liquid oxygen flows, is supplied to the top of the low pressure space of the column. The conduit i1 delivers air to the high pressure space of the column at H. The conduit It? connects with the bottom of the oxygen product space I79.

In Fig. 3 there is illustrated an arrangement for controlling the feed back of oxygen product into the liquid oxygen space of the column under control directly of the mass flow rate in the conduit 25. A balanced valve 39 has its position controlled by a diaphragm i8| subjected on its opposite sides to the pressures, at the entrance to and at the throat of a venturi E62, by conduits I83 and I84. Desirably the valve 138 may be at least cracked open during norma oxygen production, but this is not essential. If the flow through the conduit increases due to the production of more oxygen product of lowered purity, the valve 489 will be opened further and more gaseous oxygen will be bled back into the column, with a resultant decrease in the rate of oxygen production and an improved quality. In this form, as in the others disclosed, increased rate of liquid oxygen production, with impaired purity, will result in changed conditions in the conduit 25 which will be used to effect the necessary variation in the quantity of oxygen fed back into the column.

While I prefer to prevent the pressure (or the mass rate of flow) in the intake line to the booster from ever becoming such that the thermodynamic efficiency of the evaporator-condenser 80 would be reduced, nevertheless it will be appreciated that, if the booster capacity is suitably selected and if the control of the oxygen bleedback valve is made close enough to p. s. i. (in the illustration given), there could, under some conditions, be initial restriction of oxygen pro duction through the admission of warm oxygen gas to the column, followed, if the pressure rise was not halted (or the mass rate of flow of gaseous oxygen not diminished), by the restriction of liquid oxygen production through the reduction of liquid air supply to the column by reason of reduced liquefaction in the evaporator-condenser 60, as described in Paget Serial No. 230,042, filed June 5, 1951.

While there are in this application specifically described certain forms which the invention may assume in practice and certain modes of its performance from its method aspect, it will be understood that these forms and modes have been particularly disclosed for purposes of illustration, and that the invention may be modified and embodied in various other forms and practiced in other modes without departing from its spirit or the scope of the appended claims.

What is claimed is:

1. Apparatus for continuously separating a mixture of gases and recovering one of the same, with maintenance of a desired degree of purity thereof, including a pump for delivering the mixture at an elevated pressure and at a constant rate, a heat exchanger to which said pump discharges, an evaporator-condenser and an expansion engine each receiving a part of the dried and cooled mixture from the heat exchanger, a rectifying column connected to the evaporator-condenser and said expansion engine to receive the discharges therefrom, a liquid product pump arranged to take the desired gas in a liquid state from the column and to raise its pressure to one suited to its complete evaporation in the evaporator-condenser, and connected to deliver it to the latter, a booster having a suction line con nected with the heat exchanger, for compressing the warmed and vaporized gaseous product and discharging it against a constant back pressure, and means responsive to the changes in condition in said suction line as the rate of production of the product entering the same changes for diverting a portion of the vaporized gaseous product to the column space from which said productis drawn in the liquid state.

2. Apparatus as defined in claim 1 in which said means responsive to the changes in condition in the suction line as the rate of production of the product entering the same changes for diverting a portion of the vaporized gaseous product to the column space from which said product is drawn in the liquid state is responsive to the suction pressure of the booster.

3. Apparatus as defined in claim 1 in which said means responsive to the changes in condition in the suction line as the rate of production of the product entering the same changes for diverting a portion of the vaporized gaseous product to the column space from which said product is drawn in the liquid state is responsive to the mass rate of flow in said suction line.

4. Apparatus for producing oxygen at a pre 13] and in which means is provided under the control of the oxygen product in a line leading to the booster, for returning to the oxygen space of the column a portion of the vaporized oxygen product.

5. Apparatus as defined in claim. 4 in which said means under the control of the oxygen product in a line leading to the booster, for returning to the oxygen space of the column a portion of the vaporized oxygen product is responsive to the pressure of the oxygen product in the booster intake line.

6. Apparatus as defined in claim 4 in which said means under the control of the oxygen product in a line leading to the booster, for returning to the oxygen space of the column a portion of the vaporized oxygen product is governed by the mass rate of flow of the gaseous oxygen product in the booster intake line.

7. Apparatus as defined in claim 4 in which said means under the control of the oxygen product in a line leading to the booster, for returning to the oxy en space of the column a portion of the vaporized oxygen product is set to effect the return of the portion of the vaporized oxygen product at a pressure below that at which complete vaporization of the oxygen product in the evaporator-condenser would cease to take place.

8. In an oxygen-generating apparatus for suplying gaseous oxygen of a high degree of purity and at a relatively uniform rate, in combination, a plurality of heat exchangers traversed by entering air, a column for receiving air from said exchangers and delivering liquid oxygen, a liquid oxygen pump taking liquid oxygen from the column and raising the pressure thereof above column pressure, means for connecting the liquid oxygen pump discharge with said heat exchangers for utilizing in the latter the refrigeration in the oxygen, whereby the oxygen leaves said exchangers in a gaseous state, but at at least substantially the same pressure as the discharge pressure of said liquid oxygen pump, booster means for raising the pressure of the gaseous oxygen to a materially higher value, means for regulating the pressure of the oxygen discharged by said booster means to maintain the same substantially constant, and means governed by a condition at the intake side of said booster means for passing gaseous oxygen from the intake side of said booster means to the space within the column from which liquid oxygen is drawn, effective when the pressure at said intake side rises above a predetermined value.

9. Apparatus as defined in claim 8, in which there is provided means governed by the pressure at the intake side of the booster means for Icy-passing fluid from the discharge of said booster means to the suction side of the latter.

In the method of producing substantially pure gaseous oxygen from compressed air which includes moving, through an evaporator-condenser which provides for heat exchange only between entering air and leaving oxygen product, a heat exchanger and a valve device, into a column, a quantity of air, while causing liquid oxygen at a pressure above column pressure to flow through said heat exchanger and said evaporator-condenser in counterfiow relation to the entering air, the pressure of said entering air and the pressure of said liquid oxygen under pressure being such that there may be liquefaction of air and attendant complete vaporization of the oxygen in said evaporator-condenser, the

step of precluding, through 1 the diversion back to the liquid oxygen space within the. column of a portion of the vaporized oxygen varying with the time rate of production of liquid-ox.

gen, the attainmentof-a back pressure in the. oxygen course of said. evaporator condenser which will prevent complete evaporation of the liquid oxygen therein.

11. Method of continuously separating a mixture of gasesandrecovering one of the same with a maintenance of a desireddegreeof purity including delivering the mixture at: an elevated pressure and at a constant rate to an apparatus including a heat exchanger, an evaporator-condenser and an expansion engine each receiving a part of the dried and cooled mixture from the heat exchanger, and a rectifying column to which the evaporator-condenser and said expansion engine discharge, withdrawing the desired gas in a liquid state from the column and raising its pressure to one compatible with its complete evaporation in the evaporator-condenser and delivering it to the latter, conducting the desired gaseous product from the heat exchanger, and compressing it in its warmed and vaporized state and discharging it against a constant back pressure, and diverting to the column space from which said gaseous product is drawn in liquid form a portion of the vaporized gaseous product varying with the rate of delivery of the gaseous product into the suction of the booster and efiective to prevent the pressure therein from reaching a value at which complete evaporation of the product gas in the evaporator-condenser will cease to take place.

12. Method according to claim 11 in which the diverting to the column space from which the gaseous product is drawn in liquid form of a portion of the vaporized gaseous product varying with the rate of delivery of the gaseous product into the suction of the booster is varied directly with the pressure in the suction to the booster.

13. Method according to claim 11 in which the diverting to the column space from which the gaseous product is. drawn in liquid form of a portion of the vaporized gaseous product varying with the rate of delivery of the gaseous product into the suction of the booster is varied directly with the mass rate of flow in the suction of the booster.

14. Method of producing oxygen at a predetermined pressure and purity, including supplying air at a predetermined rate and pressure tothe column, for rectification therein, passing, on its way to the column, a portion of the air stream in heat exchange relation, in an evaporator-condenser, with the liquid oxygen product only, the latter being at a pressure, above the pressure at which it leaves the column, appropriate to its complete vaporization, with the liquefaction of an equivalent amount of air, boosting the pressure of the evaporated oxygen product to a predetermined higher constant pressure, and diverting from the gaseous oxygen stream, before the latter is subjected to the boosting operation and under the control of a condition in said gaseous oxygen stream which changes as the rate at which oxygen product enters such stream varies, a variable portion thereof back into the oxygen space of the column below the liquid level in'the latter.

15. The method of claim 14, in which the diversion of a variable portion of the gaseous oxygen stream back into the oxygen space of the 15 column is under the control of the pressure at the point of diversion.

16. The method of claim 14, in which the diversion of a variable portion of the gaseous oxygen stream back into the oxygen space of the column is under the control of the mass rate of flow of the gaseous oxygen stream just before the boosting of the pressure thereof.

17. The method of claim 14 in which said diversion back into the oxygen space of the column is at a pressure lower than the pressure at which complete evaporation of the liquid oxygen in the evaporator-condenser will commence not to be efiected.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Eichelman Oct. 9, 1934 Wildhack Apr. 19, 1949 Anderson Aug. 23, 1949 Anderson Aug. 23, 1949 Voorhees Feb. 28, 1950 De Baufre Apr. 11, 1950 Cornelius Feb. 13, 1951 Anderson Dec. 22, 1953