US2097434A - Apparatus for cooling and rectifying mixed gases - Google Patents

Description

Nov- 1 w. L. DE BAUFRE APPARATUS FOR COOLING AND RECTIFYING MIXED GASES Filed Nov. 9," 1935 4 Sheets-Sheet 1 INVENTOR,

ATTORNEY.

Nov. 2, 1937. w. 1. DE BAUFRE 2,097,434

APPARATUS FOR COOLING AND RECTIFQING MIXED GASES Filed Nov. 9, 1955 4 sheets-she et 2 F/G'Z W v I INVENTOR. mffaewwgfi ATTORNEYS.

Nov. 2, 1937. w. .DE BAUFRE 2,097,434

APPARATUS FOR COQLING AND RECTIFYING MIXED GASES f Filed Nov. 9, 1935 4 Sheets-Shept s FIG. 3 INVENTOR v Patented Nov. 2 1937 UNITED STATES PA-TENT OFFICE 2,097,434 APPARATUS ron COOLING AND anom- ING mxnn GASES William Lane De Baufre, Lincoln, Nebr. Application November 9, 1935, Serial No. 49,015 24 Claims. I (case-122) This invention relates to the art of separating mixed gases by cooling and rectification and is pheric air to the temperature of liquefaction,

which is necessary before the air can be subjected to rectification, water vapor is condensed out of the mixed gases as liquid water above zero centigrade and frozen out as solid ice (frost) below zero centrigrade. Carbon dioxide sublimes out of the air at temperatures below minus 80 centigrade. 4

Interchangers for cooling compressed atmospheric air have been arranged for defrosting so that it was unnecessary to remove water vapor from the air before cooling the same. But it has been necessary to warm such interchangers to atmospheric temperature at frequent intervals in order to defrost the heat transferring surfaces. Also, it has been proposed to employ recuperators for cooling air to be rectified by means of heat absorbing material previously cooled by products of rectification, ice and carbon dioxide deposited on the surface of the heat absorbing material while cooling air being re-evaporated by the pure dry products of rectification. Such recuperators, however, have many disadvantages; and, in the ordinary arrangement of air separation plants,v

ice and carbon dioxide would be carried through such recuperators and be deposited in other parts of the plant, such as the engine or turbine for supplying refrigeration thereto, thereby causing difficulties in operation and in maintenance.

The general object of the present invention is to arrange an air separation plant so that the process can be conducted satisfactorily without purifying the air of watervapor or carbon dioxide. Other objects of the invention are:

To supply to the rectifier substantially constant quantities of the atmospheric air or other mixed gases to be rectified and to withdraw therefrom substantially constant quantities of the products ofrectification in order that the rectifier will function at its highest effectiveness and the products of rectification will be of substantially constant purity ir'respective of variations in resistance to flow of the atmospheric air or other mixed gases through the cooling apparatus.

To provide means for securing any desired purities of products with high emciency both by changes in operating conditionsand by changes in design proportions. 1

To obtain one of the products of rectification without contamination by the original mixed 5 gases.

To removefrom the cooling apparatus without shutting down the plant, impurities which accumulate over a number of cycles of operation.

' To accomplish the preceding objects, an auxill0 iary cycle is provided for refrigeration purposes and for producing or augmenting the liquid and vapor refluxes required in rectification.

, A subsidiary object of the invention is to so arrange this auxiliary refrigeration cycle in com- 15 bination with the main rectification cycle that the plant may be cooled to operating temperatures by utilizing the mixed gases to be separated. And, in the process of cooling and-during normal operation, less volatile constituents will be re- 2e moved from the fluid circulated in the auxiliary refrigerationcycle, thereby making this fluid suitable for use as the liquid reflux in the main 7 rectification cycle.

The auxiliary refrigeration cycle is so arranged that the apparatus therein may be cooled to operating temperatures without cooling the rectifier in the main rectification cycle. j

The foregoing objects together with such additional and subsidiary advantages as may here- .inafter appear or are incident to the invention,

are realized by the novel method and apparatus described herein and shown in preferred form on the drawings as follows:

Figure 1 shows a schematic arrangement of an air separation plant. wherein two sets of recuperators are employed for cooling two measured portions of the air to be separated, the heat absorbing material within the recuperators being cooled by respective measured products or rectification. Figure 2 shows an'air separation plant with combined recuperators and interchangers employed as regenerators for cooling a measured portion of the air to be rectified, the products of rectification also being withdrawn inmeasured supplying measured quantities of the mixed gases thereto and removing measured quantities of the I rectification products therefrom, the mixed gases being cooled by the rectification products in com-;

bined reouperators and interchangers as regenerators.

Three different ways of utilizing an auxiliary refrigeration cycle in combination with the main rectification cycle are shown in these three figures, the auxiliary cycle in all cases contributing to the vapor and liquid refiuxes required in the main cycle. In Fig. 3, the auxiliary cycle contributes to the refluxes produced in a final stage of rectification by means of a preliminary stage of rectification. In Fig. 1 and Fig. 2 the vapor and liquid refiuxes for a single stage'rectification are produced by means of the auxiliary cycle.

Figure 4 shows in detail the arrangement of the combined recuperatpr and interchanger employed as a regenerator in Fig. 2 and Fig. 3. The means for controlling the operation of th valves through recurring cycles of operations are also shown'together with the means for controlling the warming of any one regenerator to room temperature. Figure 5 shows an alternative arrangement of heat absorbing material among the tubes of the combined recuperator and interchanger'shown in Fig. 4.

The apparatus shown on the drawings comprises:

(1) Compressor A with positive displacement cylinders B, C, D and E for supplying measured portions of atmospheric air or other mixed gases to the cooling and rectifying apparatus and for withdrawing therefrom measured portions of the products of rectification. This compressor is driven by motor M. 4

(2) Regenerators F, G, H and F, G, H, Fig. 1, for cooling the measured portions of mixed gases by heat exchange with material which has previously been cooled by the measured products of rectification. In Fig. 2 and Fig. 3, the regenerators F, G and H are combined recuperators and interchangers, the measured portion of mixed gases being cooled partly by direct heat exchange with one of the measured products of rectifica-' fier R1, preliminary rectifier R: and exchanger R3.

(4) Combined compressor and expander W with positive displacement cylinders Q and S for compressing the gas which is to be cooled and (9) Main controller K, Fig. 4, for periodically changing the fiows of mixed gases and products of rectification through the regenerators.

(10) Auxiliary controller Y for warming each regenerator in turn to room temperature in order to remove therefrom impurities which accumulate over a number of cycles of periodic changes in flow.

Operation oi the above listed equipment will be described for separating atmospheric air into more or less pure oxygen and nitrogen, for which pipe I by positive displacements of the pistons within cylinders B and C in Fig. 1 and these measured portions are suppliedto the two sets of regenerators (recuperators) F, G, H and F, G, H.

This feature of the present invention is covered in patent application Serial No. 44,616 filed Oct. 11, 1935. In Fig. 2 and Fig. 3, one positive displacement cylinder B only is required to supply a measured quantity of air since the air to be cooled is not divided into two portions.

- In all cases, the measured quantity of air to be separated is cooled substantially to the temperature of rectification by measured portions of products of rectification withdrawn by positive displacements of the pistons within cylinders D and E. As indicated in the figures, the pistons within cylinders D and E are driven by cranks on the same shaft as the cranks driving the pistons within cylinders B and C. Consequently, the positive displacements of the means for supplying the portions of air to the separation unit have a constant ratio to the positive displacements of the means for withdrawing products of rectification therefrom. Evidently, for any given pressure of the air within pipe I, there will be a corresponding pressure of rectification determined by this ratio; The volume of either portion of air or of either product of rectification willvary with the clear.-

ance volume of the compressor cylinder in question. By providing clearance pockets and valves 2, 3, .4 and 5 for opening or closing such pockets to the cylinders, the volume fiow for any cylinder may be changed at will. The flow ratio will thereby be changed either for varying the pressure of rectification, for varying the purities of the products of rectification, or for adjusting the portions of air supplied tothe cooling effects of the returning products of rectification.

Thus, it is evident that in steady operation, the mass of products removed from the rectifier must equal the mass of mixed gases supplied for rectification. The former mass is equal to the sum of the products of the densities of the components of rectification at approximately the rectification pressure and the respective piston displacements within cylinders D and E as affected by the clearance volumes. The latter mass is equal to the sum of the products of the density of the mixed gases at substantially the pressure in pipe 1 and the piston displacements within cylinders Band C as affected by the clearance volumes of these cylinders. Hence, to every pressure in pipe I there is a corresponding rectification pressure determined by the displacements and clearance volumes. Any relative change in displacements or clearance volumes will therefore change the rectification pressure relative to the pressure in pipe I. Y

The relative quantities of the products of recti- Y able the correct ratio of products for any desired purities to be attained and maintained by proper design proportions. By varying the clearance volumes, this ratio may be changed with fixed displacement volumes and corresponding changes made in the purities of the products during operation.

- As any changes in thequantities of rectification products will vary the cooling efiects in the to the cooling effects of the returning rectification products.

At low pressures of the air to be rectified relative to the pressure of rectification, as would be the case in the apparatus of Fig. 1 and .Fig. 2, clearance pockets may need to be very large for changes desired in. the ratiobf the products of rectification or of the two portions of the air to be rectified. In such cases, some equivalent means may be employed for changing this ratio, such as mounting the cranks for the air cylinders on a different shaft from that containing the cranks for the products cylinders, and then connecting the two shafts through a speed changing device, such as represented by 50 in Fig. 2 and Fig. 3. But in any case, there is a mechanical connection between the positive displacement devices for maintaining substantially constant the ratio of the two products of rectification withdrawn from the rectifier and the ratio of the mixed gases to the rectification products by driving compressor A by motor M.

Bypositive displacement means for supplying the air to be rectified and positive displacement means for withdrawing the products of rectification, rectifier R may be operated at any desired pressure of rectification, either above or below atmospheric pressure or the pressure within pipe I. By operating below atmospheric pressure, ad

vantage can be taken of the wider spread at lower pressures between compositions of liquid and. vapor in phase equilibrium, therebyincreasing the efiectiveness of any-given rectifier.

By opening any inlet or outlet pipe to the atmosphere, the pressure within the systemwill be maintained substantially at atmospheric pressure at that point. In such case, one-positive dis.-

placement compressor cylinder can be omitted and the apparatus will function in the same man ner as previously described with the exception that rectification will be conducted substantiallyat atmospheric pressure. If an inlet pipe be con,- nected directly to pipe 4 rectification will be conducted substantially at the pressure in pipe i.

Thus, in Fig. 1, if pipe 6 be open to the atmosphere or connected directly to pipe l (as shown by dotted lines) compressor cylinder C can be omitted. The portion of air drawn directly from the atmosphere or from pipe i, will be determined by the difierence between the positive displacements of cylinders B, D and E. In Fig. 2, cylinder B can be omitted and all air drawn in directly from pipe i or the atmosphere through the dotted pipe shown.

Also, one of the positive displacement cylinders, for withdrawing a product of rectification can be omitted, this product being discharged directly into the atmosphere. Then, if the air were supplied by positive displacement means, the amount of this product would be maintained substantially constant by positive displacement means for withdrawing the other product of rectification. Thus,

-over a number of cycles of operation.

be rectified and positive displacement means for withdrawing the oxygen.

Finally, one of the positive displacement compressor cylinders can be replaced by a type of compressor which is not of the positive displace- .ment type, such as a centrifugal type compressor.

Rectification will then be carried on at any desired pressure above or below atmospheric pressure as determined by the centrifugal type com- .pressor.

. In any case, all but one inflowing or outflowing fiuid must be' supplied or withdrawn by positive displacement means in order to obtain the advantages described.

By varying the speed of motor M, the displacements of all cylinders B, C, D and E are varied in proportion. The proper ratio of the two products of rectification is therefore maintained. at all capacities of operation of the plant. At the same time, the two portions of the air to be rectified aremaintained in proper relation to the two products of rectification with separate sets of regenerators as shown in Fig. i.

The air to be separated flows through pipes S and i from compressor cylinders C and B respectively to one-of regenerators F, G, H and F, G, H. A product iii-rectification returns through the remaining regenerators in parallel. By providing three ormore regenerators connected in parallel, the returning product I of rectification flows through at least two regenerators in parallel while the mixed gases flow through one regenerator. .This provides the lower velocity for the -returning product and the longer time for re-evaporation of impurities described and claimed in patent application Serial No. 44,616 filed Oct. .11, 1935. This-is true for the regenerators shown in Fig. 2 and Fig. 3 as well as in Fig. 1.

In Fig. 2 and in Fig. 3, means are shown for warming any one of the regenerators above the freezing temperature of water in order to remove therefrom impurities which have accumulated This becomes possible by having three or more regenerators in parallel so that at least one regenerator is available for warming a returning product of rectification and a second regenerator is available for cooling themixed gases while the third regenerator is being warmed above the freezing temperature of water.

Referring to Fig. 2 and Fig. 3, assume valves a, b, c, I, m, s, t and 22 open and valves e, f, h,

i, j, n, o, p, q and u closed. Then the air from cylinder i5 flows through pipe I and up through regenerator F while the oxygen product of rectification flows through pipe 8 from rectifier R. and down through tubes 9 within regenerator F. The air is cooled partly by heat transfer to the returning oxygen product of rectification within tubes 9 and partly by slightly warming heat absorbing material placed around tubes as shown in Fig. 4 and Fig. 5. The material of tubes 9 also stores up some heat. No oxygen returns through the tubes within the remaining regenerators but the nitrogen product ofv rectification flows from rectifier R through pipe It and then flows down through the heat absorbing material surrounding the tubes withinregenerators G and H. i

Any frost and sublimed carbon dioxide which have been deposited upon the surfaces of the tubes within regenerators G and H and of the heat absorbing material surrounding these tubes while air was being cooled, are more or less reevaporated and absorbed by the nitrogen product of rectification which returns from rectifier R practically free of water vapor and carbon dioxide. The returning nitrogen cools the heat absorbing material surrounding the tubes in these regenerators and also the material of the tubes themselves.v

After a period of operation in the above manner, either regenerator G or H may be substituted for regenerator F. For example, by closing valves 2 and m, the return fiowof nitrogen through regenerator G .is shut 01!. Then, by

openingvalves h, i and :i, flow of air and of reof the heat transfer tubes. Suppose that it is desired to raise the temperature of regenerator H above the freezing temperature of water in order to re-evaporate all frost and carbon dioxide snow accumulated therein. This may be accomplished by closing valve t, opening valve u and closing valve 11 in sequence. The nitrogen returning through regenerator F or G will then flow up through regenerator H.

Entering at approximately room temperature, the nitrogen will warm the heat absorbing material within regenerator H above the freezing temperature of water. Any resulting water may be removed through drain l8 shown in Fig. 4. The carbon dioxide willbe gasifiedand leave with the outflowing nitrogen.

An upward flow of the warm nitrogen through the regenerator is desirable in order that water from melted ice will run downto warmer regions within the regenerator. of the air being cooled is also desirable in order that condensed vapor will run down to warmer regions. Downward flows of returning cold oxygen and cold nitrogen are then necessary in order for these fluids to be in contraflow relation to the air cooled.

The preferred construction of such a combined recuperator and interchanger is shown in Fig. 4. Tubes 9 extend from upper fixed tube sheet II to lower floating head. I2. The returning oxygen enters through pipe 8 and. leaves through pipe l3 which passes through the packed stufllng box shown. Tubes 9 are more widely spaced than customary in interchangers for air liquefaction and separation plants. The spaces between tubes 4 order toiiause a flow of the air to be cooled across 9 contain heat absorbing 'material.

As shown in the left halfsection, such material may'consist of rods or tubes in layers with the rods or tubes in each succeeding layer crossing the rodsror tubes in the preceding layer. In

tubes Qfibaflles I 4 maybe inserted at intervals. In the right half section, the heat absorbing material is shown in theform of corrugated strips (orcylinders) i 5. In Fig. 5, the corrugations are shown in another position with plain circular sheets I placed between tubes 9 and corrugated circular sheets H. In either case, the corrugated sheets may be perforated to permit cross flow of air and nitrogen, and baflies such as I may be employed to induce such cross flow.

The floating head construction shown permits An upward fiow relative expansion and contraction of tubes and shell, both during the small temperature changes of the normal cycle of operationsand during the greater temperature changes in warming for defrosting and cooling again to normal operating temperatures. By having the shell of greater inside diameter than the outside diameter of the floating head, the heat transfer surface and the heat absorbing material may be readily removed from the 'interchanger shell. This is accom-,

plished by disconnecting at flanges 41, 48 and 5|. The plate closing the lower end of the shell and holding the stuffing box may then be lifted through the shell with the heat transfer surface and the heat absorbing material. The inside flanged connection at 48 makes this possible.

The construction described and shown facilitates manufacture and renewal of tubes and heat absorbing material after the plant is assembled. The construction is made possible by the heat absorbing material surrounding the tubes. Without such material in the spaces between the tubes, heat absorption by the tubes would be so poor as to render the construction impractical because this construction could not be employed with closely spaced tubes.

and o as in Fig. 2 and Fig. 3. Each of thesevalves may be closed by admitting an operating fluid under pressure to the cylinder containing the piston attached to the valve stem. By releasing the pressure, the valves are opened by the springs shown assisted by any excess of fluid pressure under the valve disk relative to the fluid pressure above the main disk. Controllers X and Y admit the operating fluid to the several cylinders and release it therefrom; 4

Operating fiuid is supplied under pressure through tube I 8 to controllers and Y and is exhausted through tube 20. By turning the handles indicated, pressure and exhaust tubes l9 and 2ll are brought into communication with the operating tubing running to the several cylinders. The several valves are shown in the positions for warm nitrogen returning from one or more other regenerators to flow through pipe 2| and valve e up'through the shell of the regenerator shown,

out through valve 9 and thence through pipe 49, valve vbeing closed. Valve ,1 is also closed to prevent flow of nitrogen in through valve 4, down through the regenerator and out through valve e.

Valves a and b are closed to prevent flow of air therethrough. Valve 0 is closed to prevent flow of oxygen through this regenerator while being warmed above the melting temperature of ice. Controllers'X and Y are so arranged that valve g can be opened only when nitrogen is flowing through the regenerator and cannot be opened when air is flowing therethrough. When air is flowing through this regenerator, a movement of the handle of controller Y cannot open valve f. Valve p can be closed only when valves 1 and g are moved to the positions shown for. this or one of the other regenerators. This interlocking is accomplished by arranging the tubing asshown for supply and exhaust of the operating fluid.

Thus, in the position shown for main controller X, tubing 22 is connected to pressure tube l9, thereby closing valves a, b and c. In any other position of the operating handle, tubing 22 is con- 75 a, b and 0. These three valves thus always operate together, air and .oxygen flowing through the regenerator at the same time.

In the positionshown for main controller X;

tubing 23 is connected to exhaust tube 20, thereby permitting valve e to open. Valve e is therefore always open when valves 0., b and c are closed,

and vice versa.

From valve 1, tubing 24 is connected to auxiliary controller Y instead of main controller X. Normally, tubing 24 is connected to tubing 23 within controller Y so that valve 1 opens and closes simultaneously with valve e by movement of controller X. But with the handle of auxiliary controller Y in the position shown, tubing 24 is.

connected with pressure tube l9, thereby closing valve 1. By moving the handle on controller Y, tubing 23 can be connected either with pressure 'tube i9 or with operating tubing'23. Therefore, valve 7 cannot be opened by controller Y when closed-by controller X but can be closed by controller Y when opened by controller X..

For valve 9, tubing 25 is connected to auxiliary controller Y and in the positionshown is connected to tubing 23 which is connected to exhaust tube 20 within main controller X. In any,

other position of auxiliary controller Y, tubing 25 is connected to pressure tube 19. Therefore, valve 9 can be opened by controller Y only when tubing 23 is connected by controller Xto exhaust tube 20; that is, only when valve e is open. When valve e is held closed by tubing 23 being connected to pressure tube IB-within main controller X, valve 9 cannot be opened by moving auxiliary controller Y to any position.

For valve 0, tubing 26 in the position shown of auxiliary controller Y is connected to tubing 22 which is connected within main controller X to pressure tube i9. In any other position of a'uxiliary controller Y, tubing 26 is connected to exhaust tube 28. Tubing 26 can thus be connected to pressure fluid only through tubing 22. Hence, valve 11 can be closed only when tubing 22 is con-- nected within main controller X to pressure tube i9 and valves a, b and c are therefore closed.

The arrangements of regenerators and operating vaves as previously described may be used wlth-single-stage rectification as shown in Fig. 1

and Fig. Z-or ,with two-stage rectification as shown in Fig. 3 and in patent application Serial No. 4*i,6l6 filed Oct. 11, 1935.

Referring to Fig. 1 and Fig. 2, rectifier R is a single-stage column with a vaporizer atthe bottom for vaporizing the more or less pure liquid oxygen leaving the lowest plate within'the column. to the space surrounding tubes 28 in the vaporizer. Nearly pure nitrogen vapor is condensed within tubes 28 in vaporizing the liquid oxygen. The resulting oxygen vapor leaves through pipe 29, part returning to-the column as a reflux vapor and part'returning through pipe 8 to regenerators F, G, H. The condensed nitrogen leaves through pipe 36 and is throttled through valve w onto the top plate within column R where it serves as a reflux liquid inrectifying air entering the col- .umn through" pipe 3!. n

The nitrogen which condenses within tubes 28 in Fig. 1 and in Fig. 2, is supplied by means of an aumliary refrigeration'cycle'. In Fig. 3. the nitrogen comes largely from a preliminary rectification of the air to be separated and is augmented by nitrogen from an auxiliary refrigeration cycle.

Referring to Fig.3, the two-stage rectification This liquid omgen flows through pipe 27 column is divided into a flnal rectifier R1, a preliminary rectifier R2 and an exchanger Ra. Air

to be separated enters preliminary rectifier Ra through pipe 3| and is there rectified into a nearly pure nitrogen vapor and an oxygen-rich liquid. The oxygen-rich liquid flows through pipe 44 and is throttled by valve 11 onto an intermediate plate in final rectifier R1. The nearly pure nitrogen vapor is partly condensed within the tubes of preliminary rectifier R2 to form a liquid reflux for the preliminary rectifier. The remaining nitrogen vapor flows through pipe 45 and is liquefledwithin tubes 28 of exchanger Ra. the resulting liquid nitrogen flowing through pipe 30 and being throttled through valve 10 to form. a liquid reflux within final rectifier, R1. Oxygen vapor enters final rectifier R1 through pipe 29 and forms thevapor reflux therein. Liquid oxygen not vaporized within preliminary rectifier R2 flows through valve 2 into exchanger Re where the vaporization is completed. Oxygen vapor returns through pipe 8 to regenerators F, G, H. g

With two-stage rectification, the air cooled within regenerators F, H, G, is discharged into the preliminary stage under say 50 lb. pressure as compared with being discharged into the rectifier at about atmospheric pressure with singlestage rectification. The combined recuperator 1 and 'interchanger has even greater advantages in reducing contamination of one product of rectification with two-stage rectification shown in:

eration cycle is withdrawn from the rectifier through pipe 32 connected to nitrogen return pipe ill (or to the rectifier top). In flowing through liquefier L and interchanger K, this cold. nitrogen is warmed approximately to room temperatm'e and then flows through pipe 33 to compresser cylinder Q. Here the nitrogen is compressed to about 50 lb. gauge and discharged through pipe 3!. In returning through interchanger K and liquefier L, the compressed nitrogen is cooled in K and partly liquefied in L by heat exchange with the cold nitrogen withdrawn from rectifier R. The partly liquefied nitrogen flows through pipe 35 to the vaporizer in Fig. 1 and Fig. 2 or to the preliminary rectifier in Fig. 3.

In all cases, the nitrogen vapor is liquefied within cylinder Q, is substantially equal to the pressure necessary to liquefy the nitrogen by heat transferto the oxygen being vaporized at the pressure of rectification. The compression pressure exceeds this liquefaction pressure only by the fric tional resistance to flow through interchanger K and liquefier L. Thereis thus avoided thethermodynamic loss due to a large drop in pressure.

caused 'by throttling p rtly liq rogen:

from'liquefier L to some-lower pressure before utilizing it for producing the vapor reflux in rectiiying the air to be separated. In Fig. 1 and Fig.

,2. vapor'and liquid refluxes are produced by utilizing the nitrogen of the auxiliary refrigeration cycle. In Fig. 3, vapor and liquid refiuxes produced in this way augment refluxes produced in liquefied therein. The superheated nitrogen gas fiows thence through pipe 46 to expander P. In expanding with performance of external work, the superheated nitrogen is cooled. The cooled expanded nitrogen is then exhausted through pipe 4| into nitrogen return pipe III to regenerators F, G'and H beyond the point of connection of pipe 32 to pipe Hi. It is desirable to superheat the saturated nitrogen vapor withdrawn from the vaporizer before expanding this vapor in order to obtain a more efiicient opera tion of expander P. The expander P is shown as a reciprocating engine with positive displacement of the piston up to the point of cut-off. In

many ways, however, a turbine with fixed orifice pressed to a higher pressure and discharged through pipe 31 to interchanger K. Within interchanger K, the further compressed nitrogen is cooled to a. low temperature. It does not reach the saturated vapor temperature but is discharged in a superheated condition through pipe 38 to expander P.

In Fig. 1, the further compressed and cooled nitrogen is expanded in expander P and is then discharged through pipe 39 into the vaporizer of the rectification column. Here the expanded nitrogen vapor is liquefied by heat transfento the liquid product of rectification, thereby augmenting the vapor reflux produced by liquefying the nitrogen vapor compressed just to the pressure necessary for liquefaction. The resulting nitrogen liquids commingle and are throttled through valve 10 into the rectification column as the liquid reflux. Liquefied expanded vapor thus augments the liquid reflux for rectification of the air to be separated. r g

. In Fig. 3, the further compressed and cooled nitrogen is expanded in expander P to the pressure of the final stage of rectification. At this pressure, the expanded nitrogen, further cooled by performance of external work, is discharged through pipe 4| into pipe III for nitrogen returning to regenerators F, G and H, at a point beyond the connection ofpipe 32 to pipe i3.

In all cases, T is a storage reservoir for nitrogen on the suction side of the compressor and 1; represents purifiers for removing carbon dioxide, water vapor and oil from the compressed nitrogen East a In starting the plant, particularly for the first time or inthe absence of storage tank T, the,

of carbon dioxide and frost in the refrigeration cycle at starting.

In all cases, interchanger K and liquefier L only are cooled to operating temperatures without cooling rectifier R. In Fig. 1, by-pass valve :2:

is provided for opening at starting so that the e panded gas from expander P passes directly to liquefier L and thus returns through liquefier L the rectifier. This is accomplished by connecting both discharge pipe ll and inlet pipe 32 to return pipe I 0 from rectifier R to regenerators F, G, H.

I While cooling down, valves w and y are closed so that all of the gas compressed by the pistons in cylinders Q and S is expanded in expanderP. Clearance pockets are provided on cylinders Q and S with valves 42 and 43 in order that the amount of gas compressed may be reduced while cooling down so that excessive compression pressures may be avoided, particularly while the temperature at the inlet to expander P is above normal oper- '-ating temperature.

When interchanger K and liquefier L have reached approximately operating temperatures,

- part of the compressed gas will be liquefied within liquefier L. The resulting liquid will drain through pipe 35 into thebottom of the vaporizer on rectifier R in Fig. 1 and Fig. 2. In Fig. 3, the trays within preliminary rectifier R: will fill with liquid draining through pipe 35 before any liquid accumulates in the pot at the bottom. By opening valve w slightly, liquefied gas may be discharged into the top of the rectifying column to fill the trays therein. In the arrangement shown in' Fig. 1, valve :1: may be partly cl ed to raise the pressure in order to force the liquefi d gas through valve to.

While the gaseous mixture is being liquefied within liquefier L, the liquid formed is more or less in phase equilibrium with the remaining vapor. That is, the liquid formed will contain a higher percentage of the less volatile constituent than the remaining vapor. Consequently, the

remaining gas becomes richer in the more volatile constituent of the original gaseous mixture. By

the time normal amounts of liquid accumulate within the rectifier, as shown by the level of the liquid surrounding tubes,28, the gas remaining in the refrigeration cycle will become very rich in the more volatile constituent of the mixed gases to be separated. Valve :1: is then closed.

- or other gaseous mixture to be cooled and rectified. Measured quantities of the rectification products are withdrawn at the same time.

The method of starting described will result in the rectification products having purities approaching th'ose desired as soon as normal fiows are established. Any deficiencies will soon be remedied by the method employed of drawing into the refrigeration cycle a portion of the volatile product of rectification through pipe 32 to replace the gas left therein by the starting operation. The volatile product of rectification approaches phase equilibrium with liquefied gas from the refrigeration cycle injected into the rectifier as a liquid reflux. The volatile product of rectification is therefore richer in the more volatile constituent of the mixed gases than the gas in the refrigeration cycle. The gas in the refrigeration cycle therefore becomes progressively richerin the volatile constituent of the mixed gases rectified until the volatile product ofrectification reaches the purity for which the apparatus is proportioned. The less volatile product of rectification will also reach the purity corresponding to the proportions of the rectifier and the auxiliary apparatus.

Exhaust pipe 4| from expander P in Fig. 2 and Fig. 3 is connected to pipe In from rectifier R to 'regenerators F, G, H at a point farther from rectifier R. than the point of connection to inlet pipe 32 to the refrigeration cycle. This is done so that expanded gas will not be returned through the refrigeration cycle but will bereplaced by a fresh:

portion of the more volatile product of rectification.

During normal operation, valve w is regulated to maintain a nearly constant liquid level in the pot of the vaporizer in Fig. 1, and Fig. 2. In Fig. 3, valves to and y are regulated to maintain constant liquid levels in the pots of exchanger Ba and preliminary rectifier R2. In all cases, the liquid level surrounding tubes 28 is self adjusting if proper design proportions are employed. 1

Thus, this liquid level determines the wetted surface of tubes 23 which establishes the temperature difierence necessary to condense nearly pure nitrogen vapor within tubes 28 by vaporizing nearly pure oxygen liquid outside these tubes.

For any given temperature difference, there is a pressure of condensing nitrogen vapor corresponding to the rectification pressure at which the oxygen liquid is vaporized. In- Fig. 2, this condensing nitrogen; pressure is substantially the initial pressure to expander P. The external.

work of expander P and the refrigeration furnished thereby to balance heat leak and other thermodynamic losses in the whole process, is a function of the initial pressure. The system will settle down to a liquid level surrounding tubes 28 at which the refrigeration furnished is just equal to that required. Should insumcient refrigeration be supplied, the liquid level will drop until therise in the pressure of condensation results in increased refrigeration sufiicient to balance the requirements. Should the supplyof refrigeration be in excess of the requirements, the liquid level will rise until a new balance is reached at a lower initial pressure to expander P.

In Fig. 1 and Fig. 3, the same automatic balancing of refrigeration supplied to that required,

is obtained'by compressorcylinder S withdrawing a measured quantity of gas from the discharge pipe of compressor cylinder Q substantially at the pressure ofcondensation of nitrogen within tubes 28. Should this pressure rise, a greater mass of gas would be withdrawn by cylinder S and supplied to expander P. The initial pressure of expansion would' therefore rise and more refrigeration be furnished until a balance -is reached between supply and demand.

During normal operation of any one of the plants shown, main controller 1:, Fig. 4, is moved periodically to change the flows through regenerators F, G, E. This controller might be driven at a slow constantspeed by an electric motor. By this means, the valves are operatedas pre= viously described to cool two or more-regenerators by a rectification product while a single regenerator is'being warmed slightly by air or other mixed gasep to be rectified. At intervals, one of the regenerators through which a rectification product returns, is substituted for the regeneratorv cooling the mixed gases.

At longer intervals after a number of cycles of such operation, each regenerator is in turn warmed above zero centigrade by operating auxiliary controller Y in order to remove frost and carbon dioxide accumulated therein.

During normal operation, the correct properin the ratio of the rectification products or of the portions of mixed gases may be made during operation however, by means of valves 2, 3, l and 5 controlling clearance pockets in the several cylinders or by some equivalent means such as the speed changing device shown as at. 50 in Fig. 2-and Fig.3.

I claim:

1. Apparatus for cooling and rectifying mixed gases including regenerators for cooling the mixed gases and for warming the products of rectification, positive displacement means driven in synchronism for supplying said mixed gases and for withdrawing said products of rectification in measured quantities except one portion of the mixed gases or one product of rectification, and means for maintaining such portion or product at nearly constant pressure whereby the rectification-pressure remains substantially at said constant pressure.

2. Apparatus for cooling and rectifying mixed gases including positive displacement means driven in synchronism for supplying said mixed gasesand for withdrawing rectification products, regenerators for cooling the mixed gases supplied and warming the rectification products withdrawn, a rectifier for rectifying the cooled mixed gases into a vapor product and a-liquid product,

means for withdrawing a portion of said vapor product at the temperature of rectification, means for warming the portion withdrawn and for cooling and partly liquefying said portion after compressing it to a higher pressure, a compressor for compressing said portion, a vaporizer for vaporizing the liquid product of rectification and liquetying the cooled compressed portion of said vapor product, means for utilizing the liquefied portion of said vapor product as a liquid reflux in said rectifier, and an expander for expanding with performance of external work a fraction of the portion 'of said vapor product withdrawn whereby refrigeration issupplied to said rectifier to balance heat leak and other thermodynamic losses.

3. Apparatus for cooling and rectifying mixed gases including positive displacement means driven in synchronism-for supplying said mixed gases and for withdrawing rectification products, regenerators for cooling the mixed gases supplied and for warmingthe rectification products withdrawn, a preliminary rectifier for rectifying the cooled mixed gases into a vapor component and a liquid component, a final rectifier for rectifying said liquid component into a vapor-product and a liquid product, heat transfer means for vaporizing said liquid product and iiquefying said vapor component, means for utilizing part of the vaporized liquid as'a vapor reflux in the final rectifier,

means for utilizing liquefied component as a liquid reflux in said final rectifier, means for withdrawing at-the temperature of rectification a portion of the vapor product from said final rectifier, means for warming the portion withdrawn and cooling and partly liquefying said portion after compressing it, a compressor for compressing said portion to the pressure within said preliminary rectifier, means for introducing the partly'liquefied portion into said preliminary rectifier whereby the vapor and liquid refluxes are augmented in said final rectifier, and an expander for expanding with performance of external work a fraction of the portion of said'vapor product withdrawn whereby refrigeration supplied to said rectifiers to balance heat leak and other thermodynamic losses.

4. Apparatus for rectifying mixed gases including a rectifier, means for withdrawing therefrom a portion of the more volatile product of rectification at the temperature of rectification, a liquefier and interchanger for warming said portion and recooling and partly liquefying said portion after compressing it, means for compressing said portion, means for expanding a fraction of said portion with performance of external work to furnish refrigeration to said rectifier, and

means for cooling said liquefier and said inter changer to operating temperatures without cooling said rectifier.

5. Apparatus for rectifying mixed gases including a rectifier, means for withdrawing therefrom a portion of the more volatile product of rectification at the temperature of rectification, a lique-.

fier and interchanger for warming said portion and for recooling and partlyliquefying said portion after compressing it, a compressor for compressing said portion, a vaporizer for liquefying said portion in producing vapor reflux within said rectifier, an expander for expanding a fraction of said portion with performance of external work and means for withdrawing said fraction from said vaporizer.

6. Apparatus for rectifying mixed gases including a rectifier, means for withdrawing a portion of the more volatile product of rectification therefrom, a liquefier and interchanger for warming said portion to room temperature, means for compressing said portion to the pressure at which it is liquefied in vaporizing the less volatile productof rectification, means for further compressing a fraction of said portion, means for passing said fraction through said interchanger whereby said fraction is cooled, an expander for expanding the cooled fraction with performance of external work, means for passing the remainder of said portion through said interchanger and said liquefier whereby the remainder is cooled and partly liquefied, and a vaporizer for vaporizing the less' volatile product of rectification by liquefying said remainder. a.

7. Apparatus for rectifying mixed gases as in claim 6 including. means for discharging the expanded fraction of the more volatile product of rectification-into said vaporizer whereby said expanded fraction is liquefied in vaporizing the-less volatile product of rectification.

8. Apparatus for rectifying mixed gases as in claim 6 including means for com-mingling'the expanded fraction of the more volatile'product of rectification with the more volatile product of rectification after withdrawing a portion for warming in saidliquefier and said interchanger.

9. Apparatus for rectifying mixed gases as in claim 5 including means for passing said fraction through said llquefier whereby said fraction is superheated before being expanded.

10. Apparatus for rectifying .mixed gases including a rectifier, an outlet pipe for discharging the more volatile product of rectification therefrom, a refrigeration cycle for furnishing refrigeration to said rectifier, means for withdrawing a portion of the more volatile product of rectification from said rectifier, and for utilizing said portion as the refrigerant in said refrigeration cycle,

and means for discharging the refrigerant from said refrigeration cycle into said outlet pipe beyond the point of withdrawal of said portion whereby a fresh portion of the more volatile prod-' not of rectification is continuously withdrawn to serve as refrigerant in the refrigeration cycle.

, 11. Apparatus for cooling and rectifying mixed gases including multiple regenerators which are alternately cooled by a, product of rectification and warmed by said mixed gases flowing through the same spaces withinsaid regenerators, and

7 means for warming one of said regenerators above the freezing temperature of water while the re- .trol mechanism for warming one of said regenerators above the freezing. temperature of water for vaporizing frost and carbon dioxide accumulated therein without interrupting cooling and rectifying of the mixed gases.

13. Apparatus for cooling and rectifying mixed gases as in claim 12' wherein the auxiliary control mechanism is interlocked with the main control mechanism whereby one of said regenerators can be ,warmed above the freezing temperature of water by means of the auxiliary control mechanism only when the main control mechanism is set for flow of said product of rectification through said regenerator, and the auxiliary control mechanism cannot interrupt. the flow of said mixed gases through said regenerator when the main control mechanism is set for such flow. 14. In apparatus for cooling and rectifying mixed gases, a combined interchanger and recupe'rator for coolingthe mixed gases by heat transfer through heat transfer surface to one product of rectification and by heat transfer to heat abso'rbing material previously cooled by another product of rectification, including a shell, a fixed head and tube sheet at one end of said shell, a'

floating head and tube sheet at the other end of said 'shell, tubes extending between the two tube sheets, heat" absorbing material between said tubes, and baflles between said tubes and within said heat absorbing material whereby the mixed gases are caused to flow across said tubes and among said heat absorbing material.

15. A combined interchanger and recuperator as in claim 14 wherein said tubes are arranged in circular rows and said heat absorbing material .'.comprises circular sheets of corrugated material.

16. Apparatus for cooling and rectifying mixed gases including regenerators for cooling the mixed gases and for warming the products of rectification, and positive displacement means driven in synchronism for withdrawing said products of rectification in measured quantities, whereby the quantities of said products of rectification are maintained in substantially the same ratio irrespective of the operating capacity of the apparatus.

1'1. Apparatus for cooling and rectifying mixed gases including regenerators for. cooling the mixed gases and for warming the products of rectification and positive displacement means driven in synchronism for supplying said mixed gases and for withdrawing said products of rectification in measured quantities, whereby the quantities, of said mixed gases and said products of rectification are maintained in substantially the same proportion irrespective of the operating capacity of the apparatus and the frictional resistances to flow of said mixed gases through said regenerators.

18. Apparatus for cooling and rectifying mixed gases including separate regenerators for cooling separate portions of said mixed gases by warming the respective rectification products, and positive displacement means driven in synchronism for supplying said separate portions to said separate regenerators and for withdrawing therefrom said respective rectification products, whereby the separate portions of said mixed gases are proportioned to the cooling effects of therespective rectification products irrespective of the opcrating capacity and the frictional resistances to fiow of said separate portions through said sepa-- rate regenerators.

19. Apparatus for cooling and rectifying mixed gases including a rectifier, a refrigeration cycle comprising a compressor for compressing a're- 'frlgerant, an expander for expanding said refrigerant with performance of external work, an interchanger for warming said refrigerant and for recocling the refrigerant after being compressed,

- and a liquefier for warming said refrigerant and liquefying a fraction of the compressed refrigerant, means for returning expanded refrigerant to the liquefier and interchanger without passing it through the rectifier whereby the interchanger and liquefier can be cooled to operating temperatures without cooling the rectifier. i

20. In apparatus for ,cooling and rectifying mixed gases, a rectifier including a vaporizer for vaporizing theliquid product of rectification, a-

refrigeration cycle for supplying refrigeration to balance heat leak and other thermodynamic losses 65 in said rectifier including an expander for expanding a refrigerant and means for introducing it into said vaporizer where said refrigerant is liquefied in vaporizing the liquid product of refrigeration, and a by-pass for said vaporizer with valve therein whereby the expanded fluid may be returned-to said refrigeration cycle without fiowingthrough said vaporizer by opening said valve.

21. Apparatus I for rectifying mixed gases including a rectifier, a refrigeration cycle for furnishing refrigeration to said rectifier by expandin'g'a refrigerant from an initial pressure, a va-' porizer for vaporizing liquid from said rectifier and liquefying refrigerant from said refrigeration cycle, a positive displacement compressor for compressing said refrigerant from the pressure of liquefaction in said vaporizer to said initial pressure in the refrigeration cycle, whereby the refrigeration requirements of said rectifier-are automatically balanced by the refrigeration supplied by said refrigeration cycle.

22. In apparatus for cooling and rectifying mixed gases, a rectifier including a vaporizer for vaporizing the liquid product of rectification, a

refrigeration cycle for supplying refrigeration tobalance heat leak and other thermodynamic losses in said rectifier, an expander for expanding the refrigerant in said refrigeration cycle, a compressor for compressing the refrigerant to a pressure at which it will liquefy in said vaporizer'by vaporizing .the liquid product of rectification, a

second compressor for compressing said refrigerant to a pressure from whichexpansion in said expander will supply said refrigeration, and means for operating said expander and said compressors in synchronism. p v

23. In apparatus for cooling and rectifying mixed gases as in claim 22, means for reducing the capacity of said compressors relative to said expander whereby an excessive compression pressure is avoided at starting.

24. In apparatus for cooling va'ndrectifylng mixed-gases, a combined interchanger and recuperator for cooling the mixed-gases by heat transfer through heat transfer surfaceto one product of rectification and by heat transfer to heat absorbing material previously cooled by another product of rectification, including a shell, a fixed head andtuhe' sheet at one end of said shell, a floating head and'tubej sheet at the other end of said shell, tubes extending between the two tube sheets arranged in circular rows, and heat absorbing material between said tubes comprising sheets of corrugated material.

Mamba moms.

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