US2460859A - Method of gas separation including impurity removing steps - Google Patents

Description

P. R. TRUMPLER METHOD OF GAS SEPARATION INCLUDING MPURITY REMOVING STEPS Filed May l, 1944 Feb. s, 1949.

IN VEN TOR.

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T N /fv 5f l w A/Jyoz w f A y ATTORNEY Patented Feb. 8i, 1949 METHOD OF GAS SEPARATION INCLUDING IMPURITY .REMOVING STEPS Paul R. Trumpler, Westfield, N. J., assigner to The M. W. Kellogg Company, Jersey City, N. J., a corporation of Delaware Application May 1, 1944, Serial No. 533,608

(c1. ca -175.5)

17 Claims. 1

This invention relates to an improved method for the separation of gas mixtures containing` lower and higher boiling components and other components which boil at still higher temperatures. More specifically, it is concerned with a continuous method for the separation of air into a substantially oxygen-containing fraction, and a. substantially nitrogen-containing fraction and elimination from the air of undesirable impurities, such as water vapor and carbon dioxide or other high boiling components.

The separation of low-boiling gas mixtures, Ifor example air, into relatively pure 4components heretofore has been accomplished by processes involving expansion, liquefaction, and fractionation. In processes of this character, cold exchangers have been employed to precool the gas mixtures by counter-current heat interchange with backward-returning cold product material. When the process is conducted under high pressure the undesirable higher boiling impurities, such as water vapor and carbon dioxide or hydrocarbons, are eliminated by the employment of switch cold exchangers or by adsorbers and absorbers. However, when the separations are con ducted under relatively low pressures, only the aforementioned switch cold exchangers generally are utilized to remove the higher-boiling components. One major diiculty prevalent in such use of switch exchangers arises from the fact that the water, carbon dioxide, or other comparatively' higher boiling components in the air will precipitate therefrom as a solid. and accumulate in the exchangers in deposits great enough to plug up the passageways of these vessels. The plugged exchanger then has to be switched with an unplugged one and thawed out before again being used. Consequently, the economy of a system using switch exchangers in this manner is greatly reduced because of the necessity to cover the cold losses.

The separation of air, or other normally gaseous mixtures, into the relatively pure components also has been accomplished by a method which includes compressing and precooling of the mixture, liquefaction at the initial pressure of a portion of the mixture by heat interchange with cold products of the separation, the expansion of another portion with external work, fractionation of the two portions in a common fractionating tower at the lower pressure, and backward return of the products of separation. In this arrangement, precooling has been accomplished by means of two sets of cold regenerators which operate in periodically reversing cycles between the incoming feed air and the backward-returning cold products. Such regenerators often are utilized in the additional capacity of removing water, carbon dioxide or other impurities, that is, when these impurities are deposited on the metal surfaces of the regenerator as the air is cooled they are sufficiently re-evaporated therefrom during the reversed phase of the cycle as to obviate the necessity of frequent thaWin-gs. The transfer of heat between the reversing streams of fluid depends, of course, upon the storage of heat or cold in the metal packing of the regeneratorsv during each phase of the cycle. Consequen-tly, regenerators have the disadvantage that the incoming and outgoing streams are never in simultaneous thermal contact with each other across a common heat interchange boundary, and for this reason the cycle time in the regenerators affects the heat'transfer eiliciency, as well as the quantity of the deposited impurities accumulated in the regenerators. y

In contra-distinction to the use of regenerators, a counter-current reversing cold exchanger system more recently has been developed which permits a simultaneous and eicient heat interchange between passageways containing countercurrently flowing streams of air and backward returning cold products. This exchanger comprises a plurality of parallel paths for the fluid in each passageway which are so metal bonded together as to establish a metal to metal thermal contact throughout the whole contact length of the vessel. Likewise the several passageways of the exchanger are joined with metal to metal contact. Reversing cold exchangers of this type, therefore, are characterized by possessing a high rate of heat transfer, and a thermal efficiency unaffected by cycle time, since little dependence is placed on storage of heat in metal.

These reversing cold exchangers are also normally utilized to remove almost all of the higher boiling impurities from air, or other gaseous mixtures, particularly for separations conducted at relatively low pressures, such removal being accomplished by periodically alternating the flow of warm incoming feed and a backward-returning cold product between at least two passageways of the exchanger. That is, during one half of the reversing cycle when the air is being cooled, water and carbon dioxide, for example, are precipitated therefrom and accumulated in solid or liquid phase on the metal surfaces of the passageway through which the air at that time is owing. Then, before thev accumulation has become great enough to plug that passageway the counter-currently flowing streams are interchanged to enable the backward-returning product to flow over the accumulated deposits and re-evaporate them. Meanwhile, the air is being cooled and precipitating further quantities of impurities on the metal surfaces of the alternate passageway through which the backward-returning product previously has been flowing. It is understood, of course, that the re-evaporation usually is carried out with that product of the separation whose recovery in the pure state is not desired, or from which the impurities can subsequently be more readily separated, although a stream, or streams, of backward-returning pure product normally is caused to pass through a separate passageway of the same exchanger, to recover the cold therefrom while maintaining the pure product in an uncontaminated form.

In any event, the Water and carbon dioxide impurities deposited either in reversing regenerators or cold exchangers, are substantially completely removed only if conditions inuencing complete re-evaporation of the impurities are effectively maintained throughout the region, or regions, of the apparatus containing deposits of these materials. 'I'hese conditions relate speciiically to a provision for a sufficient volume of gas into which the deposits can be evaporated and removed, and to the maintenance of a sufficient vapor pressure of the deposited impurities as is governed by the temperature of the backwardreturning product gas in the region of said deposited impurities.

It is to be understood that, as the impurities are usually deposited in apparati of these types at one temperature and are removed at some lower temperature, the smaller the difference between these two temperatures the greater is the rate of re-evaporation. That is, a small diierence in these temperatures means there is only a small difference between the existing vapor pressures of the impurities at the time of their precipitation and re-evaporation. If the ratio of the Vapor pressures is equal to the ratio of the volume of gas from which the impurities have been removed to the volume of gas re-evaporating them, then the backward-returning products by becoming saturated with the impurities are capable of removing substantially all of the impurities from the system at the same rate at which they have been deposited within the system. It may be necessary, however, to maintain the temperature difference at any point in the region of the passageway containing impurities somewhat less than the above described theory would require in order to compensate for incomplete saturation of the evaporating gas or for a drifting of the solidified impurities to colder locations in the passageway during the half cycle during which they are being deposited. It is obvious therefore that eventual plugging of passageway can be avoided only if the impurities deposited in half a cycle are completely removed in the other half cycle for all cycles of the operation.

Heretofore, particularly in installations for the recovery of oxygen from air that involve the use of regenerators, water and carbon dioxide impurities have been removed by passing an equal, or even greater, quantity of backward-returning product gas over the impurities than the quantity of air from which they were deposited. This condition has been attained by introducing into the system at an intermediate point an additional quantity of high pressure air which has been previously puriied. In the separation of gas mixtures by a method which incorporates the use of reversing cold passageways and where recourse to the foregoing expedient is not taken, a smaller mass quantity of a backward-returning cold product is available for evaporation of solidied impurities than the mass quantity of gas from which the impurities -were initially removed. Thus, with less mass quantity volume of evaporating gas available, higher vapor pressures, or in other words, higher temperatures, are required to compensate for the smaller gas mass quantity. This means that smaller temperature differences are required between the gas being purified and the backward-returning evaporating gas in the regions of the passageways in which impurities are beingremoved.

It is an object of my invention to provide for obtaining these small temperature differences in any desired region of a reversing counter-current exchanger or regenerator in which evaporation of solidied higher boiling impurities is being accomplished with less mass quantity of backward-returning gas than the mass quantity of feed gas from which they were precipitated. I accomplish this by causing the temperature of the cold backward-returning product to approach the temperature of the feed gas mixture in those regions of an exchanger or regenerator where precipitation of impurities occurs, or contrari- Wise by bringing the temperature of the feed gas closer to that of the cold product, or by causing the temperatures to approach each other simultaneously. I do this by properly designing auxiliary heat interchange means and providing for eiicient thermal contact between the gas caused to pass through this means and the heretofore stated regions of an exchanger or regenerator.

Accordingly, I induce an abstraction oi heat from the exchanger or regenerator by this auxiliary heat interchange means, which may be considered as being of the nature of a regulated artificial heat leak, from those regions in which the temperature differences between the countercurrently flowing gases would be normally too great for re-evaporating substantially all of the impurities. For instance, the foregoing effect is achieved in connection with the use of a reversing cold exchanger in the separation of air by diverting a proportion, or all, of cold backwardreturning low pressure nitrogen-containing product through a suitably designed auxiliary heat interchanger which is properly attached to the reversing exchanger so as to abstract a desired amount of heat from a given region, or regions. The diverted proportion is then recombined with the main body of nitrogen-containing product before its introduction into reversing, or other, passageways of the exchanger. Or alternatively, the proportion diverted may comprise the compressed incoming air and in this case it is removed from and returned to the main body of air subsequent to the passage of the feed through the exchanger. Or again, proportions of both backward-returning product and incoming air may be passed simultaneously through separate passageways in the auxiliary heat interchange means. In this manner any desired temperature diierence between the IloW- ing fluids can be main 'ned over any desired region in the exchanger. T e foregoing described diversion of fluid through an auxiliary heat interchange means unbalances the normal temperature relationship between the feed air and the nitrogen-containing product passing in counter-current heat exchangewith each other to an extent sumcient to establish conditions suitable to bring about re-evaporation of the deposited solid impurities by less mass quantity of expanded output product than the air from which they' were precipitated.

In the accompanying drawings, Figure 1 is a diagrammatic ow sheet depicting one exemplary embodiment of my invention in connection with an illustrative processing arrangement for -producing pure oxygen from air by a continuous low pressure method, involving reversing cold exchangers, which is capable of operations of long duration. While the items of equipment shown in the drawing for illustrative purposes are particularly designed for use in a small mobile plant adaptable to installation on the chassis of a motor truck, it is to be understood that the present invention is equally adaptable to large commercial plant installations. Furthermore, the present invention is not limited in its scope to processes involving the separationof air, since it is equally applicable to separations of other gaseous mixtures which contain higher boilingy impurities such as, for example, rare gases and normally gaseous hydrocarbons. In the embodiment shown in Figure 1, backward-returning low pressure nitrogen-containing productis utilized in the auxiliary heat interchanger to carry out the invention. Figure 2 shows a portion of the owsheet of Figure 1 and illustrates the alternative modification in which a portion of the compressed incoming air, subsequent to the passage of the air through the exchanger, is utilized in the auxiliary heat exchanger to carry out the invention.

Referring now to the drawing, atmospheric air which in this instance is at 120 F. and atmospheric pressure and which preferably 'has been filtered is drawn into the first stage compression chambers I, 2, 3, and 4 of compressor 5 through intake ports 6, 1, 8, and 9. Compressor 5 is shown on the drawing as being a comparatively small and compact air cooled compressor which is driven by an air cooled internal combustion engine I0, especially adaptable for use in a mobile type plant, The partially compresed air is discharged from the first stage compression chambers through outlet lines II, I2, I3, and I4 respectively into line I 5 and conveyed therethrough to intercooler I6. In intercooler I6, the temperature of the air is reduced to about 135 F. Usually, as there is no condensation of water from this temperature reduction in intercooler I6, the cooled air is passed directly to compression chambers I1 and I8 by way of lines I9 and 20 respectively for a second stage compression to the desired final operating pressure which, in the present instance, is about 105 lbs. per square inch absolute. At this pressure the air leaves compression chambers lI1 and I8 through lines 2l and 22 respectively, at about 410 F., whereafter they are combined in line 23 for passage to aftercooler 24. Aftercooler 24 and intercooler I5 comprise nnedtube heat exchangers cooled by a blast of fandriven air. In passing through the aftercooler the temperature of the air again is reduced to about 135 F. This reduction in temperature at the nal pressure condenses most of the water vapor which is withdrawn by a means not shown on the drawing. The partially dried air is then passed to filter chamber 25 by way of line 25 for removal of oil carried over from the compressor, or other impurities such as light hydrocarbons. Upon leaving filter 25 through line 2l the air may have the residual amounts of water removed by passage through an adsorber means, again not shown on the drawing. In any event, the air is discharged from line 21 into the inlet port of reversing valve 23. Exchanger 29 is shown in line 21 for heating the illtered air'with hot effluent from the second stage of compressor l which is taken from and returned to line 23 by lines 3l and 3i respectively. Since heat exchanger 29 is an auxiliary apparatus for delivering an emergency supply of hot air through line 21, it normally is not in use.

During the operation in one phase of the reversing cycle, the now substantially dried and filtered air is taken through the four-way reversing valve 2B and passed through the inner annuli 32, 33, 34, and 35 of reversing cold exchangers 39, 31, 39, and 39 respectively. These reversing exchangers may have their annuli and center passageway packed with a continuous coil of edgewound metal ribbon 31 closely bonded to the metal walls of the exchangers, or the exchangers may be otherwise constructed, a primary requisite being that the passages are metal to metal bonded to -provide a small thermal resistance to the conduction of heat. Optionally there may be only one exchanger having the necessary heat exchange surface. In passing through annuli 32, 33, 34, and 35, the pressured air is in countercurrent .heat interchange with the cold products of its subsequent separation, as sha-ll hereinafter be described. By such heat interchange the temperature of the pressured air is lowered during its passage through cold exchangers 35, 31, and to approximately minus F. and it is at this temperature that the air enters the last cold exchanger 39 in the series. In cold exchanger 39 the temperature of the air is further reduced to the order of about minus 253 F. after which it is withdrawn through line 40, check valve 4I and line 42 and introduced into surge drum 43. During its course through the foregoing temperature reduction, the pressured air deposits residual amounts of water on the metal surfaces of the exchangers as liquid and frost and similarly its carbon dioxide constituent is laid down as a solid normally in the last annulus 35 of exchanger 39, so that the air leaving this annulus through line 40 is substantially free of carbon dioxide. One function of surge drum 43 is to separate any carbon dioxide snow which may have been carried out of exchanger 39.

The purified and cooled air leaving surge drum 43 through line 44 is divided into two fractions. The larger fraction which represents in the present instance approximately 59% of the pressured air is taken through line 45 to lquefier 45 for heat interchange with cold backward-returning, nitrogen-containing product. Bypassing through coil 41 of the liquefier the temperature of this portion of the pressured air is again further rey duced to about minus 274 F. to effect partial condensation and in this condition the air is thereafter introduced by way of line 49 into the inside of reboiler calandria 48 of fractionator 50. Since the temperature of the partially liquefied air is of the order of about minus 274 F., it is warmer than the bath of liquid oxygen in which calandria 48 is submerged. Consequently, the air gives up heat to reboil the bottoms of fractionator 50 and in so doing reaches a temperature of about minus 278 F. This temperature causes total condensation of the air to liquid which liquid is thereafter removed from calandria 49 through line 5I for passage through carbon dioxide filter 52 and expansion through valve 53 into the top of fractionator 50. Simultaneously, the smaller portion of the air from line 4 4, representing approximately 41% thereof, is introduced by way of line 54 into expander 55 wherein its pressure is re-A duced with work to about 25 pounds per square inch absolute and its temperature correspondingly lowered to the order of minus 304 F. Under these conditions the expanded air is caused to flow through line 56 having surge drum 51 disposed therein, and injected as vapor feed into fractionator 50 at an intermediate point somewhat below the point of introduction of liquid air from line 5i. By-pass line 85, having valve 86, connects line 56 with line 1i for starting up purposes during the period when the air is incompletely cooled.

Vapor to liquid contact is secured in fractionator 5U which brings about separation of the air into a bottoms product which is essentially pure oxygen and an overhead product which contains a preponderance of nitrogen. Pure oxygen vapors are removed from fractionator 50 through drawoi line 58 located immediately above the liquid body of this material in the reboiler section of fractionator 50. Any entrained liquid oxygen is separated from the vapors in separator 5S and returned to the fraotionator through line 60. Vaporous oxygen leaves the top of separator 59 through line 6i at a temperature of about minus 288 F. and is passed through the center passages 62, 63, B4, and 65 respectively of reversing exchangers 36, 31, 38, and 39 for countercurrent heat exchange against incoming pressured air which is now passing through annuli 32, 33, 34 and 35 in the present phase of the reversing cycle before it is discharged at a nal temperature of 126 F. as product through line 6B.

The nitrogen-containing output product is removed as vapor from the top of fractionator 50 through line 61 at a temperature which is of the order of about minus 290 F. Usually, all of this product is passed from line B1 into line 68 for the counter-current heat interchange in liquefer 46 in which event it is returned to line 61 through line 69. However, it may be desirable at times to by-pass a proportion of this nitrogen-containing stream around the liqueer vin which case valve is used to control the by-passed proportion. In any event, the total nitrogen-containing stream is caused to flow from line 61 into line 1| at a temperature of about minus 275 F. for backward return through the aforementioned reversing eX- changers 39, 38, 31, and 36 respectively. A temperature of about minus 275 F. at the inlet to the cold end of the exchanger 39, however, is too cold relative to an exiting temperature of minus 253 F. of the pressured air at this end to evaporate all the solid carbon dioxide in the reversed passage 80 of the exchanger through which this output product now ows in the present phase of the reversing cycle. Therefore, in accordance with the present invention, a definite proportion of this cold product is diverted from line 1I through line 12, controlled by valve 13,in an amount which is dependent upon the operating conditions in the system and the thus diverted cold product is conveyed through line 12 to heat interchange means 14 for abstracting heat in a desired manner over desired areas of exchanger surface in reversing exchanger 39. Although the heat interchange means 14 is shown as a coil circumferentially around exchanger 39, the invention is not necessarily limited to this form of heat exchange means. For instance, the cold product flowing from line 12 may he passed as readily through any-passageway of exchanger 39 such as,

' complete re-evaporation is obtained.

for example, the center passageway 62 and the oxygen cold interchange then eiected by means of an additional annulus. In any event the diverted proportion of cold product leaves heat interchange means 14 at a somewhat higher temperature level through line 15, whereafter it is returned to the main stream of cold product emitting from line 'il through control valve 16 andv the commingled material, in the present phase of the reversing cycle, is then caused to pass through line 11, check valve 18 and line 19 into outer annulus of exchanger 39. In this manner the temperature of the commingled vapors as they enter annulus '80, in the present instance, is made to be of the order of about minus 262 F. which establishes a temperature difference at the cold end of exchanger 39 between the incoming pressured air and backward-returning product of about 9 F.

The 9 F. difference is less than the maximum allowable temperature difference between the air and product necessary to provide for vapor pressures of the carbon dioxide in these gases that will satisfy the vapor pressure and volume ratio relationship at which complete evaporation of the solid carbon dioxide, or carried-over ice, deposited in annulus 80 during its previous use for the cooling of the pressured air, can be accomplished. It is to be understood, of course, that this temperature diiierence does not usually remain constant at about 9 F. over the effective heat exchange surface of reversing exchanger 39 because of the nature of the heat balance involved in this kind of counter-current ow. It is to be understood further, that heat interchange means 14 may be expanded to embrace other regions in the cold exchanger system in which the existing temperature dilerences may be greater than the a1- lowable maximum temperature differences for complete re-evaporation of precipitated deposits in the reversing passageways such as, for example, where water or ice have been deposited. Usually, however. the actual temperature difierence existing in such regions is less than the maximum allowable and obviates therefore the necessity for creating an unbalanced condition in the warmer regions of the exchanger system. Hence, by extending an auxiliary heat interchange surface over any given region, or regions, of the cold exchanger system in which precipitated deposits accumulate and passing a portion, or all, of one of the cold low-pressure backwardreturning output products therethrough before passing this product in reverse contact with such accumulations, what amounts to the equivalent of more low-pressure output product now is provided for heat interchange than there is pressured air with which it is exchanging heat and by thus unbalancing the normal heat interchange relationship in such region, or regions, of an otherwise conventional counter-current heat exchange system, the necessary operating temperature difference between the reversing streams for In other words, the foregoing may be visualized as being of the nature of an internal recycle of some of the low pressure output product.

By reason of the metal bonded packing and the bonded passages employed in these reversing exchangers, as heretofore described, it is economical to design these passages in such a way that the metal temperature, which is substantially uniform at any cross-section remains substantially unchanged upon reversal. As a conse- 9 quence, there is no substantial variation in the heat exchange relationship between the reversing gas streams because of interchanging their channels of ow, or in other words, no substantial regenerative heat effect is created because of the reversal and the heat interchange relationship continues to function in the same manner as though no reversal of flow of the gas streams had occurred- Further, in the event that a non-reversing stream of gas, for example the oxygen product, is passed continuously through a separate passage of the reversing exchanger, the result of the presence of this stream is to cause an independent counter-current heat exchange eifect between it and the pressured air which effect is independent of the positioning of the non-reversing stream with respect to the other gas streams in the exchanger.

The heat interchange and re-evaporation of precipitated deposits are continuously maintained in reversing cycles in accordance with the foregoing described method for one phase of a cycle by periodic manipulation of the valve settings of reversing valve 28 and the automatic cooperation therewith of the check valves in the valve manifold of which check valves 4I and 18 are members. In this way, the cold nitrogen-containing product is made to pass alternately in succession through Aannuli 80, 8l, 82 and 83 and annuli 3'5, 34, 33 and 32 respectively while the incoming pressured air is causd to pass alternately in succession through annuli 32, 33, 34 and 35 and annuli 83, 82, 8| and 80 respectively. The warmed ellluent nitrogencontaining output product thereafter leaves the system through line 84.

As stated above, an alternative embodiment of the invention involves utilization of a portion of the compressed incoming air, after passage through the exchanger, as the cooling medium for use in the auxiliary heat interchanger. This embodiment is illustrated in Figure 2 in which parts identical in function to similar parts in Figure 1 are identified by the same reference numeral as in Figure 1, with the subscript a. In Figure 2 a portion of the compressed incoming air, after passing through exchanger 39a, is diverted from line 42a. In this arrangement line 12a connects line 42a with auxiliary heat interchange means 14a, line 15a connects the exit of heat interchange means 14a, with line 42a, and valve 16a is located in line 42a between the points of diversion and return of the portion of the compressed air. By thus connecting lines 12a and 15a to line 42a and relocating valve 16a the incoming compressed air, after passage through the exchanger, is drawn on for the cooling means to be passed through the heat interchange means 14a. The embodiment illustrated in Figure 2 operates otherwise in the same manner as that of Figure 1.

As heretofore stated, the present invention is equally applicable to processing arrangements of the described character which incorporate the use of reversing regenerators in place of the reversing cold exchangers 36, 31, 38, and 39. In this event -pairs of regenerators are separately used to exchange heat between the incoming pressured air and the backward-returning output products. While the auxiliary heat interchange means comparable to means 14 shown on the drawing may be used in connection with both .pairs of regenerators, usually it is suii'lfcient for -the normal continuous operation of such plants to utilize the Imethod of this invention in connection with the -pai-r of regenerators which are exchanging heat between incoming pressured air and nitrogen-containing output product. In such case the auxiliary heat interchange means is located in the colder regions of each regenerator and the stream of incoming pressured air or output product passing thereto is divided so as to pass through each auxiliary heat interchange means in parallel ilo-w, the direction of flow being from the cold towards the warm region of each regenerator. This flow may be carri-ed out continuously through both regenerators of a pair, irrespective of the phase of the reverse cycle, or the flow may be intermittent with respect to each regenerator and dependent. upon the phase in being.

Itis to be understood that my invention-is not to be limited to any of the embodiments described herein for illustrative purposes but only in an-d by the following claims.

I claim:

l. In apparatus forthe separation of gas mixtures at low temperature, a heat exchanger to effect cooling of a lcompressed gas mixture by countercurrent heat exchange contemporaneously with at least one stream of cold expanded output components of the separation which comprises a reversing `countercurrent heat exchanger comprising at least two metal bounded and metal bonded fluid conduits for countercurrently conducting and effecting countercurrent heat exchange between said compressed gas mixture and said expanded output components, metal `packing in said 'fluid conduits, said packing being metal bonded to said fluid conduits, means for conducting fluid streams of said compressed gas mixture -and expanded output components to and from said conduits, valve means for controlling ow of said fluid streams, means -f-or periodically so changing said valve means as to alternate the flow of said fluid streams between said fluid conduits, a separate fluid conduit, having metal packing metal bonded thereto, disposed in juxtaposition and metal bonded to said fluid conduits adjacent the inlet thereto of said stream of cold expanded output components, means for passing a portion of said cold expanded output components through saidseparate fluid conduit, means for combining the thus-passed portion with another portion of said cold expanded output components and means for passing the combinedV ptions of said output components to said means for conducting the fluid stream of output components .to said fluid conduits as said fluid streamof cold expanded output component.

2. In apparatus for the separation of gas mixtures at low temperature, a heat exchanger to eifect cooling of a compressed gas mixture by countercurrent heat exchange contemporaneously with at least one stream of cold expanded output components of the separation which comprises a reversing countercurrent heat exchanger comprising at least two metal bounded and metal bonded fluid conduits for countercurrently conducting and effecting countercurrent heat exchange between said compressed gas mixture and said expanded output components, metal packing in said fluid conduits, said packing being metal bonded to said fluid conduits, means for conducting fluid streams of said compressed gas mixture and expanded output components to and from said conduits, Valve means for controlling flow of said fluid streams, means for periodically so changing said valve means as to alternate the flow of said fluid streams between said nuid conduits, a separate fluid conduit, having metal packing metal .bonded thereto, disposed in `uxtaposition and metal bonded to said fluid conduits adjacent the inlet thereto of said stream of cold expanded output components, means for passing a portion of the th-us-cooled compressed gas mixture through said separate fluid conduit, means for combining 4the thus-passed portion with the portion -of the cooled compressed gas mixture not passed through said separate fluid conduit.

3. In a method of separating a gaseous mixture into its components, wherein a compressed gaseous stream of said mixture, the components of which differ in boiling points in their liquid states, is passed in one direction of iiow through a reversing heat-exchange zone along a precooled path therein progressively decreasing in temperature from end to end to eilect cooling of the stream and resultant precipitation of a component of. higher boiling point in a colder portion of said path and wherein a second gaseous stream free of the last mentioned component and under lower pressure and at lower temperature than said colder portion is passed subsequently through the same path in the opposite direction of iiow after the rst stream has ceased ilow; the step of increasing the temperature of the second mentioned stream before suchpassage by diverting a portion thereof through a separate parallel path in said heat interchange zone disposed in heat exchange relation with the colder portion of said path to increase the temperature of the said diverted portion of said second mentioned stream, then combining the latter with the remaining portion of said second mentioned stream, and then eiecting said subsequent passage of the second mentioned stream in the opposite direction and over the precipitate and thereby causing removal thereof.

4. In a method of separating a gaseous mixture into its components, wherein a compressed gaseous stream of said mixture, the components of which differ in boiling points in their liquid states, is passed in one direction of flow through a reversing heat-exchange zone along a path therein progressively decreasing in temperature from end to end to eiect cooling of the stream and resultant precipitation of a component of higher boiling point in a colder portion of said path and wherein a second gaseous stream i'ree of the last mentioned component and at lower temperature than said colder portion is passed r subsequently through the same path inv the opposite direction of ilow after the rst stream has ceased flow; the step of increasing the temperature of the second mentioned stream before such passage by diverting a portion thereof through a separate parallel path in said heat interchange zone disposed in heat exchangerelation with the colder portion of said path to increase the temperature of the said diverted portion of said second mentioned stream, then combining the latter with the remaining portion of said second -mentioned stream, and then effecting said subsequent passage of the second mentioned stream in the opposite direction and over the precipitate and thereby causing removal thereof.

5. In a method of separating a gaseous mixture into its components, wherein a compressed gaseous stream of said mixture, the components of which differ in boiling points in their liquid states, is passed in one direction of flow through a reversing heat-exchange zone'along a path therein progressively decreasing in temperature from end to end to eiect cooling of the stream and resultant precipitation of a component of higher boiling point ina colder portion of said path and wherein a second gaseous stream free of the last mentioned component and at lower temperature than said colder portion is passed subsequently through the same path in the opposite direction of flow after the first stream has ceased flow; the step of increasing the temperature of the second mentioned stream before such passage by diverting at least a portion of the constituents thereof through a separate parallel path in said heat interchange zone disposed in heat exchange relation with the colder portion of said path to increase the temperature of@ the said diverted portion of said second mentioned stream, and then effecting said subsequent passage of the second mentioned stream in the opposite direction and over the precipitate and thereby causing removal thereof.

6. In a method of separating a gaseous mixture into components, wherein a compressed gaseous stream of said mixture, the components of which differ in boiling points in their liquid states, is passed in one direction of flow through a reversing heat-exchange zone along a cooled path therein progressively decreasing in temperature from end to end to effect cooling of the stream and resultant precipitation of at least one component of higher boiling point in a colder portion of said path and wherein a second gaseous stream obtained from the gaseous mixture after said precipitation is passed subsequently at a lower temperature than said colder portion through the same path in the opposite directionl of iiow after the 'rst stream has ceased flow therethrough; the step of controlling the tem-I perature of said colder portion of said path by passing at least a portion of the constituents of the second mentioned stream through a separate path in said heat-exchange zone disposed in heat exchange relation with at least a part of said colder portion of said first mentioned path.

7. In a method of separating a gaseous mixture into its components, wherein a compressed gaseous stream of said mixture, the components of which differ in boiling points in their liquid states, is passed in one direction of flow through a reversing heat-exchange zone along a cooled path therein progressively decreasing in temperature from end to end to effect cooling of the stream and resultant precipitation of a component of higher boiling point in a colder portion of said path and wherein a second gaseous stream free of the last mentioned component and at lower temperature than said colder portion is passed subsequently through the same path in the opposite direction of iiow after the first stream has ceased iiow; the step of controlling the temperature of said colderportion by diverting a portion oi the iirst mentioned stream after such passage through a separate path in said heat interchange zone disposed in heat exchange relation with the colder portion of said rst mentioned path.

8. In a method of separating a gaseous mixture into its components, wherein a compressed gaseous stream of said mixture, the components of which differ in boiling points in their liquida states, is passed in one direction of flow through a reversing heat-exchange zone in heat exchange with counterflowing uid along a path therein progressively decreasing in temperature from end to end to eiect cooling of the stream and resultant precipitation of a component of higher boiling point in a colder portion of said path and wherein a second gaseous stream comprising at least a portion of said counterflowing uid and 13 substantially free of the last mentioned component and at lower temperature than said colder portion is passed subsequently through the same path in the opposite direction of flow after the rst stream has ceased flow therein; the step of controlling the temperature of said colderportion of said path by passing a portion of a gaseous stream, obtained from the gaseous mixture after the precipitation of the component of higher boiling point, in countercurrent heat exchange with said compressed gaseous stream through a separate path in said heat-exchange zone disposed in heat exchange relation with at least a part of said colder portion of said flrst mentioned path to further cool said mixture to maintain a difference between the temperature at which said precipitation occurs at any point in said colder portion and the temperature at which said second gaseous stream flows past said point which is less than would exist but for the passage of said fluid stream through said separate path.

9. In a method of separating a gaseous mixture into components, wherein a compressed gaseous stream of said mixture, the components of which diil'er in boiling points in their liquid states, is passed in one direction of ow through a reversing heat-exchange zone in heat exchange with counterowing iiuid along a cooled path therein progressively decreasing in temperature from end to end'to effect cooling of the stream and resultant precipitation of at least one component of higher boiling point in a colder portion of said path and wherein a second gaseous stream, comprising at least a portion of said counterflowing fluid and obtained from the gaseous mixture after said precipitation is passed subsequently at a lower temperature than said colder portion through the same path in the opposite direction of flow after the rst stream has ceased iiow therethrough; the step of controlling the temperature of said cold portion of said path by passing a portion of a gaseous stream, obtained from the gaseous mixture after the precipitation of the component of higher boiling point, in countercurrent heat exchange with said compressed gaseous mixture through a separate path in said heat-exchange zone disposed in heat exchange relation with at least a part of said colder portion of said rst mentioned path to further cool said mixture to maintain a difference between the temperature at which said precipitation occurs at any point in said colder portion and the temperature at which said second gaseous stream flows past said point which is less than would exist but for the passage of said uid stream through. said separate path.

10. A method in accordance with claim 4 wherein said reversing heat-exchange zone has at least two separate parallel paths in heat exchange relation with each other, the compressed gas stream being conducted through one of said paths while the second mentioned stream is simultaneously conducted through another of said paths.

11. A method in accordance with claim 7 wherein saidreversing heat-exchange zone has at least two separate parallel paths in heat exchange relation with each other, the compressed gas stream being conducted through one of said paths while the second mentioned stream is simultaneously conducted through another of said paths.

12. In a method of separating a gaseous mixture into its components, wherein a. compressed 14 gaseous stream of said mixture, the components of which differ in boiling points in their liquid states, is passed in one direction of ow through a reversing heat-exchange zone in heat exchange with counterllowing fluid along a path therein progressively decreasing in temperature from end to end to effect cooling of the stream and resultant precipitation of a component of higher boiling point in a colder portion of said path and wherein a second gaseous stream comprising at least a portion of said counterfiowing fluid and substantially free of the last mentioned component and at lower temperature than said colder portion is passed subsequently through the same path in the opposite direction of iiow after the first stream has ceased flow therein; the step of controlling the temperature of said colder por-` tion of said path by passing a fluid stream in countercurrent heat exchange with said compressed gaseous stream through a, separate path in said heat-exchange zone disposed in heat exchange relation with at least a part of said colder portion of said iirst mentioned path to further cool said mixture to maintain a difference between the temperature at which said precipitation occurs at any point in said colder portion and the temperature at which said second gaseous stream flows past said point which is less than would exist but for the passage of said iiuid stream through said separate path.

13. In a method of fractionating air into nitrogen-rich and oxygen-rich product fractions wherein a stream of compressed air, containing carbon dioxide as an impurity, is passed in one direction of flow through a reversing heat exchange zone in heat exchange with counterilowing product fluid not greater in mass quantity than said compressed air stream along a path therein progressively decreasing in temperature from end to end to cool said stream of air and precipitate carbon dioxide in a colder portion of said path, and wherein a second gaseousstream predominantly nitrogen, comprising at least a portion of said counterowing product fluid, substantially free of carbon dioxide and at a lower temperature than said colder portion of said path is passed subsequently through the same path in the opposite direction of flow after the air stream has ceased flow therein; the step of in'- creasing the temperature of 'the second mentioned stream before such passage by diverting at least a portion of the constituents thereof through a separate path in said heat exchange zone disposed in countercurrent heat exchange relation with said compressed air stream in at least a part of the colder portion of said path to further coolsaid compressed 4air to maintain a difference between the'temperature at which said precipitation occurs at any point in said colder portion and the temperature at which said oxide as an impurity, is passed in one direction of ilow through a reversing heat exchange zone in heat exchange with counterowing product fluid not greater in mass quantity than said compressed air stream along a cooled path therein progressively decreasing in temperature from end to end to eiect cooling of the stream of air and resultant precipitation of carbon dioxide impurity in a colder portion of said path and wherein a second gaseous stream predominantly nitrogen, comprising at least a portion of said counterflowing product iiuid, substantially free of carbon dioxide and at lower temperature than said colder portion of said path is passed subsequently through the same path in the opposite direction of ilow after the air stream has ceased flow therein; the step of controlling the temperature of said colder portion of said path by diverting and passing a part of said stream of compressed air, after such passage in countercurrent heat exchange with said counterowing product uid, through a separate path in said heat exchange zone disposed in heat exchange relation with at least a part of said colder portion of said rst mentioned path to further cool the stream of compressed air to maintain a diiierence between the temperature at which said precipitation occurs at any point in said colder portion and the temperature at which said second gaseous stream iiows past said point which is less than would exist but for the passage of said diverted part of said stream of compressed air through said separate path.

15. In a method of separating a gaseous mixture into its components, wherein a compressed gaseous stream of said mixture,` the components of which dier in boiling points in their liquid states, is passed in one direction of iiowthrough a, reversing heat exchange zone in heat exchange with counterflowing uid not greater in mass quantity than said compressed gaseous stream along a path therein progressively decreasing in temperature from end to end to etfect cooling of the stream and resultant precipitation of a component of higher boiling point in a colder portion of said path and wherein a second gaseous stream comprising at least a portion of said countertlowing iiuid and substantially free of the last mentioned component and at lower temperature than said colder portion is passed subsequently through the same path in the opposite direction of iiow after the rst stream has ceased flow therein; the step of controlling the temperature of said colder portion of said path by passing a uid stream in countercurrent heat exchange with said compressed gaseous stream through a separate path in said heat exchange zone disposed in heat exchange relation with at least a part of said colder portion of said first mentioned path to further cool said mixture to maintain a difference between the .temperature at which said precipitation occurs at any point in said colder portion and the temperature at which said second gaseous stream ows past said point which is less than would exist but for the passage of said fluid stream through said separate path.

16. In a method of separating a gaseous mixture wherein a compressed gaseous stream of said mixture is passed in one direction of flow through a, reversing heat exchange zone in heat exchange with a counterlowing product fluid not greater in mass quantity than said compressed gaseous stream and at lower pressure along a path therein progressively decreasing in temperature from end to end to effect cooling of the stream and resultant precipitation of an impurity in a cold- 16 er portion of said path, wherein a second gaseous stream comprising sat least a portion of said counterflowing fluid and substantially free of the last mentioned component and at lower tempera. ture than said colder portion is passed subsequently through the same path in the opposite direction of iiow after the first stream has ceased .iiow therein, and wherein said cooled stream is fractionated into at least two product fractions in a fractionating system comprising a fractionating zone, at least one stream of said precooled mixture passing to said fractionating zone and separate streams of product fractions owing from said fractionating zone; the step of controlling the temperature of said colder portion of said path by passing through a separate path in said heat exchange zone disposed in heat exchange relation with at least a part of said colder portion of said first mentioned path. a separate cooling stream obtained from said fractionating system to further cool said mixture to maintain a diierence between the temperature at which said precipitation occurs at any point in said colder portion and the temperature at whichsaid second gaseous stream flows past said point which is less than would exist but for the passage of said uid stream through said separate path.

17. In the method of treating air, wherein a stream of compressed air, containing carbon dioxide as an impurity, is passed in one direction of iiow through a reversing heat exchange zone in heat exchange with relatively cool counteriowing iiuid obtained from said air stream in a later stage of treatment and not greater in mass quantity than said air stream along a path in said heat exchange zone progressively decreasing in temperature from endto end to eii'ect cooling of the air stream and resultant precipitation of said carbon dioxide impurity in a colder portion of said path and wherein a second gaseous stream comprising at least a portion of said counteriiowing fluid and substantially free of the carbon dioxide impurity and at a lower temperature than said colder portion is passed subsequently through the same path in the opposite direction rof flow after the rst stream has ceased ow therein;` the step of controlling the temperature of said colder portion of said path by passing a uid stream in countercurrent heat exchange with said compressed air stream through a separate path in said heat exchange zone disposed in heat exchange relation with at least a part of said Acolder portion of said iirst mentioned path to further cool said compressed gaseous stream of air to maintain a difference between the temperature at which said precipitation occurs at any point in said colder portion and the temperature at which said second gaseous stream flows past said point which is less than would exist but for the passage of said iiuid stream through said separate path.

PAUL R. TRUMPLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,979,682 Frankl Nov. 6, 1934 2,039,889 Debaufre May 5,` 1936 2,089,558 Karwat Aug. 10, 1937 2,252,739 Stoever Aug. 19, 1941

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