US2071763A - Process for the separation of gas mixtures - Google Patents

Description

Feb. 23, 1937. F. PoLLrrzER ROCESS FOR THE SEPARATION OF GAS MIXTURES Filed Nov. 4, 1930 2 SheetJs-Sheei'I 1 Feb. 23, 1937. F. PoLLlTzER 2,071,763

PROCESS FOR THE SEIPARA'IYICN'OFm GAS MIXTURES Filed Nov. 4, 1950 2 Sheets-Sheet 2 Patented Feb. 23, 1937 .PROCESS FOR THE Germany, assigner, b Union Carbide and SEPARATION oF GAS MIX'rUltEs Franz vIollitzer,V Grosshesselohe,

y mesne Carbon Corporation, a

near Munich, assignments, to

corporation of New York Applicaabn November 4,1930, lserial No. 493,375

' In Germany March 10, 1930 claims (ci. sz-175.5)

The processes at present inuse for' the separation of gas mixtures by cooling to low temperatures presuppose, as is well known, a preliminary removal from the gas mixture of vsuch components as will become separated in a solid state on' cooling. If this removal, either by a physical or chemical process, is incomplete, the working period of the apparatus used inthe separation is shortened by the solid deposits formed. When separating gaseous products of destructive distillation, such as coke oven gases, there is added tothe diiiiculties caused by separation of water vapor, carbon dioxide and acetylene in the solid state, as a further difliculty the formation of easily decomposable or explosible substancesfrom the condensed hydrocarbons and nitrogen oxides, because these accumulate constantly during operation in the apparatus used for the separation andv cause the explosive destruction of the apperature. The cooling of the gases,

paratus when it is warmed to normal temperatures.

The present invention 'avoids entirely these diiiculties and renders superfluous the cumbersome and expensive cleaning. processes of the gases in the preparation for'cooling to low temespecially in the range of temperatures in which the above mentioned components are deposited in solid state, is carried out according to the new process by means of periodically interchanged regenfrom the compressor and the cold separation products pass in alternation, while the transfer of the refrigeration from the outgoing to the incoming 1 gases is eiected by thevregenerator. In passing through the regenerator the easily condensible impurities separate from the incoming gas in solid form, while inversely the cold outgoing gases being free from the impurities are capable of `absorbing'a certain amount of the impurities on their Way through the regenerator and of carrying them out of the same. The impelling force for the re-evaporation of the solid deposits is proportional to the difference between the vapor pressureof the solid deposits at any point of the'` regenerator and their partial pressure in the gas which passes that point.

In actual practice in-the low-temperature separation 'of gases the conditions are exactly opposite to those required by the above relation, for

at every point ofthe regenerator the temperature during condensation must always' be higher than during re-evaporation.

- Furthermore re-evaporation is made more difiicult by the factthat the amount of gas avail- 'the regenerator.

able for the re-evaporation is frequently smaller than the amount of fresh gas. This is the case, for example, when one of the products of decomposition is to be obtained. separately in pure state. In such a ca this product must not be taken' out through the regenerator, since it would become contaminated withr the impurities previously deposited therein. Hence only a fraction of the amount of gas-.which passes through the regenerator as fresh gas'is available for lthe reevaporation.

Now I havev discovered a method which insures the complete re-evaporation of the deposited impurities even where only a fraction of the amount introduced as fresh gas is available for the purpose and where there are considerable differences between the temperature of condensation and of re-evaporation. For this purpose I so adjust the pressure of the incoming gas that at every point of the regenerator Where condensation takes place the product of the partial pressure of each condensation product and the effective total volume is smaller during the intake period than is the product of the like factors during the outgo period at the same point of yT he term effective total volume is usedy in the4 specification and-claims to denote the volume of gas passing argiven point in the regenerator during a given period of'time,

Eo; 1 7-;9=l1 cubic meters In general the pressure of the fresh gas may be made even slightly higher than corresponds to the minimum pressure determined bythe above relation in order to have for the re-evaporation a suicient partial pressure difference between the condensate and the absorbing gas. The con- "densation of the gas at a higher pressure re- Aqures of course a higher expenditure of energy.

But this energy can be utilized, for example, when y tion at ordinaryl pressure, or when separating a carrying out rectification processes, by letting a v rectification under pressure precedea rectificay nitrogen-hydrogen mixture from the coke oven gas byl low temperature cooling under pressure for the synthesis of ammonia Where the produced mixture of nitrogen-hydrogen is needed underpressure. `Furthermore it is possible also to take advantage of the increased pressure of the fresh 'gas in such a way asr to cause the separation products released from pressure topass with great velocity through the regeherators, whereby a s'aving of heat exchange surfaces and hence of the cost of construction can be effected. The elimination of the preliminary purification of the fresh gas for .removing water, carbon dioxide, acetylene and the like impuritues, which in the known low temperature process had to be removed prior` to low temperature heat exchange, results in a considerable savingin theV cost of construction as well as `of operation. ,In the separation of,

coke oven gas or other ycombustible gas mixtures impurities. For this purpose the whole amount of fresh gas must be passed through the regeneratorand be cooled. But this is possible only if the entire amount of the decomposition products is made to exchange heat with the fresh gas and passes through the regenerator. Now

if one of the separated products is to be obtained "in a pure state and a contamination even with very small amounts of foreign matter isto be absolutely, avoided, as is the case, for instance, with a mixture of nitrogen-hydrogen produced for the synthesis of ammonia, it becomes necessary to take special measures for the passage of the pure products through the regenerator.

I accomplish this by conducting the pure product through conduits which are in heat-conducting relation with the filling mass of the regenerator so that the gas transmits its heat content to the entering fresh-gas by way of the storage' mass without becoming contaminated.

` The invention :Is illustrated by way of example I by means of the accompanying drawings in which:

Fig. l represents a schematic representation in partial section of one embodiment of the invention; I f

Fig. 2 represents a schematic representation in partial section of another embodiment of the invention; and

Fig. 3 is a schematic representation of a particular application of the invention. Fig. 1 represents a pair of regenerators I land 2,which are adapted for carrying out this process. 3, as well as bundles ofpipe 5, which are in heatconductive relation with the filling material. The fresh gas passes through the valve 'I into the regenerator I, deposits its impurities there, and at I3 pasfses through valve 8 to the separation apparatus not shown in the drawings. separation products, the residual gas'enters at I2, passes by way of valve 9 through regenerator 2 which at this time is not traversed by the fresh ofthe regenerator 2, gives off its cold there without absorbing'the impurities, and leaves the re- Ihe regenerators contain illling'material Of the ed separately enters at Y generator at valve II or the product' tobe obtained separately may be passed in parallel through the pipe bundles of both regenerators.

means of the valves at regular intervals; in such a Way that the fresh gas alternately passes unnecessary. at low temperatures the separatetreatmentof In Fig. 2 there schematically represented a group of regenerators I, 2 and'3, with the switching valves 4, 5, for the fresh gas, 6, l, for the residual gas, and 8, 9, for the product `which is to be obtained separately. With the switching valves in the position shown the fresh gas passes through the regenerator I, the residual gas from the separation-apparatus enters at I2 and by way of valve 6 passes to the regenerator 2, and the other product to be obtained separately en` ters at I4 and is carried .by way of the 'valve 8 through the' rege/nerator 3. During this period of operation the impurities coming from the fresh gas are deposited in the regenerator I, in regenerator 2 they are re-evaporated andcarried out,

Aand the vseparately obtained gas which must not absorb any impurities passes through the third regenerator which during the preceding operative period was freed of impurities. In the succeeding period of operation the fresh gas coming from I passes through 3, the residual gas coming from I2 passes through the regenerator I, and the product coming from I4, which is tobe obtained separately, passes through the regenerator 2 which'had been cleaned in the preceding period of operation. In the third period the fresh gas passes through 2, the residual gas cleans the regenerator 3, and 4the third gasA passes through the regenerator I.

The process willbe described for purposes of illustration by a definite example, namely by the separation of carbon monoxide from illuminating gas,vwith reference to Fig. 3.

'Ihe solution of this important problem has seemed hitherto economically impossible with the means at the disposal of the lowI temperature technician. Only by the elimination of the expensive preparatory cleaning of the gas and by the substantiall reduction of the cost of the apparatus by employing regenerators for cooling the gas has an economically usefulv solution of the problem been obtained.

Illuminating gas which has been compressed to a pressure ofv 5 to 10 atmospheres, without a preparatory purification for the removal of carbon dioxide, water vapor or other impurities (except tar and sulphur) enters at I and passes through the regenerator 2, which is filled, for example, with massive, tightly packed strips o1' sheet iron having a largearea.. Previous `to this the regenerator has been cooled down so much Ythat during an operation period which may last vSwitching of the gas streams is effected by regenerator I and confrom 1 to 3 minutes the gas leaves at nearly the vtemperature which prevails'at the lowest .point of the regenerator. Duringi the passage of thev fresh gas its impurities such as water or carbon *l minus C.;v ried out by counter current heat exchange, and' amines fresh gas freed from its impurities nowreaches, by IWay of the valve, the bundle of tubes of the counter-current heat exchanger 6, in which the rising. gas current is cooled, with rectification efy fect, to such an extent that the main part ofthe methane is separated at 1. The liquidmethane is expanded through the valve 8 into the space of the counter current heat-exchanger 6 surrounding the bundle of tubes. `The gaseous resi-` due of the fresh gas passes into the tube bundleof the counter current heat-exchanger 9, in which bundle the main portion of the-carbon monoxide is liquefied. The liquid carbon monoxide separated at I0 is expandedthrough valve I'I and serves for coolingxcounter current heat-exchang ers 9 and 6. The remainder of the gas which has not been liquefied and is composed mostly of hydrogen is reheated in the counter current collector 9 and at I2 enters the expansion engine I3, in which it cools'down doing work and furnishes at the sa'rne time the amount of cold required for the process. The cold expanded gases are returned at Htc-the counter current .he'atexchangen at I5 they pass, together with the 4liquid methane "expanded through valve 8., into the counter current return by way of switchy valve th'rough the conduit I6 into the regenerator 3 where they reevaporate the solid and liquid deposits. At I8 the gas charged with impurities is carried oi.

The fraction IIof the carbon monoxide obtained separately passes by way of the pipe bundle 4 hthrough the regenerator 3 and transmits its'.l cold tothe regeneratorv mass. After the lapse of a 4deilnii'eperiod the is changed in such a way that the fresh gas direction of the. gas currents passes through the regenerator 3, the cold gases pass through .the regenerator'Z, which in consequence of absorption of heat from the freshgas have .become-somewhat'warmed up, and so on with regular uniform alternation. The method ofoperation with threed regenerators shown by Fig. 2 Krnayvalso bevv employed for the removal of --carbon monoxide.

` If the 'gas mixtures to be cooled contain very easily condensibleccnstituents, such as benzol hydrocarbons, it is advantageous to remove these substances by connecting ahead of the regenerators .apparatus for cooling the gas down to about The cooling in this-first'step is carnot until after theseparation of the benzol is 'the regenerator cooling employed. .The solid benzoiV can be melted'and drawn. off by heating the 'cooler 'afterfa more or less ex` deposited in the cooler rtended period of operatiomJ I claim:, 1r A process mixtures into components. which'comprises cooling an inflowing gas mixture by contant-with a exchanger 6 and finally for the sparation ofgaseous `body by contact with another separated comv vponent, periodicallyalternating the flow of inA going gas and outgoing higherl and lower boiling .components with respect to a given regenerative' body, and contacting the ingoing gas and outgoing higher and lower boiling components with a given regenerative body in cyclic succession. 3. A process for the separation'of gas mixtures 'into components, which comprises -separating -a gas mixture into higher and lower boiling com ponents at a low temperature, passing separatedv higher and lower boiling Lcomponents'in heat exy change' contact relation to the surface of 'aregenf erative body in-cyclic 'succession to transfer their cold to such-body,`and then .passing a subsequent charge of the gas mixture in continuation of the cyclic succession in heat exchange contact relation with the same surface of said body whereby said gas mixture is chilled.

4. A method of separating gas mixtures containing nitrogen, carbon monoxide, and methane,

which comprises compressing said gas mixture,.

mixturerst` through cold ret the condensation of impurities then through a plurality of conducting the generators to effe contained therei countercurrent rectifying devices to separate fractions of intermediate boiling point leaving an uncondensed remainder, expanding said remainder with production of external work to cool. the

same, passing the expanded and cooled remainder in heat'exchanging relation with a portion of the inccrninggas mixture, conducting separated com-` ponnts through cold regenerators simultaneously -with the residualgas relation therewith, and periodically reversing the iw of the incoming gas mixture and of the .out,

W' Vgoing residues through said regenerators to `evapimpurities condensed therein, the cycle crate the of gas 'flow being; so arranged that the period of -flow of the incoming gas mixture through aregene'raton is followed by fa period of iiow of aA separation product such as will not be detrimentally aected by@ the evaporation thereinto of the condensates to be evaporated, whereby the nregeizierator'is placed in the desired condition to conduct the pure sepa-ration product therethrough -withoutconta1ination o`f the same, andpassi'ng the said puried product through said regenerator for` transferring refrigeration thereto.

and in heat exchanging` FRANZ Pourrzna;

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