US2416255A - Method and apparatus for condensing metallic vapors - Google Patents

Description

Feb.' 1s, 1947.

' T. GRISWOLD, JR.; ET AL METHOD AND APPARATUS FOR CONDENSING METALLIC VAPORS Filed March' 24, 1945 2 Sheets--Sheet A 2 I N VEN TORS Tk omas H.

Thomas Gn'swo/q/Jn v ATTRNEYS Patented Feb. 18, 1947 METHOD AND APPARATUS FOR CON- DENSING METALLIC VAPORS Thomas Griswold, Jr., and Thomas H. McConica, III, Midland, Mich., assignors to The Dow Chemical Company, Midland,

tion of Michigan Mich., a corpora- Application March 24, 1945, Serial No. 584,630

(Cl. 'l5-'66) 7 Claims.

This invention relates to an improved method and apparatus for condensing metal vapors.

In certain metallurgical processes, a mixture of ore and reducing agent is heated to liberate the metal as a vapor in admixture with other gases,

it then being necessary to condense the vapor to convert the metal to usable form. One of the Y most eiective condensing methods consists in passing the vapor mixture into contact with a relatively cool quenching liquid, which serves to shock-chill the metal vapor and to convert it to the liquid or solid state, usually in the form of a solution or suspension in the quenching liquid. The condensed metal iS then recovered from the quench liquid by distillation, settling, or other simple means. This quench method is especially advantageous in those processes in which the metal vapor and other gases tend to interact chemically during the condensation step, with consequent loss of valuable metal. Typical instances are met in the recovery of magnesium andof sodium from mixtures with carbon monoxide,such as are formed in the vcarbothermal processes for making these metals.

In the past, most quench condensing processes have been carried out by means of spray chambers, splash-plate condensers, bubble-towers, and similar absorption apparatus. Unfortunately, such equipment does not always provide a sufliciently drastic quench to arrest completely chemical interaction between metal vapor and accompanying gases, so that part of the 'metal may never be recovered in usable form. In addition, there may also be some loss of quench liquid by entrainment in the gases exhausted from the f These losses, while not such as, toy

condenser. outweigh the. advantages of liquid quench condensation, have constituted real practical dimculties for some time. Y

It is therefore anvobjectof the present invention to provide an improved procedure ,for condensing a metal vapor by means of 'a quenching liquid which voids the diilculties mentioned. Another object isv to provide kapparatus which effects extremely rapid and intimate contact be tween metal vaporand quench liquid and which minimizes entrainment losses. Y ,Y l

In condensing metal vapor in accordance with leaves through the orice 9 as a. high velocity` the invention, the quenching liquid,1us1allyA a 2 of quench liquid. An extreme intimacy of contact between vapor and quench liquid is thus achieved, and instant, virtually complete condensation of the metal takes place. Fixed gases in the vapor mixture pass through the streams of quench liquid and are withdrawn from beyond them.

A more detailed discussion of the invention may be made with reference to the accompanying drawings in which Fig. lillustrates, in vertical partial cross-section, one arrangement of apparatus for condensing metal vapors; and

Fig. 2 is a cut-away perspective view of the distributor and collector for quench liquid as viewed from the furnace end, showing the platelike streams of falling liquid. l

For the sake of example, the process will be described as applied to the production of magnesium by heating a charge mixture of magnesium oxide and carbon to form a vapor mix-v ture of magnesium and carbon monoxide, and condensing the magnesium vaporV by means of a lead-magnesium alloy as the quenching fluid.

In the equipment illustrated, the magnesiumcarbon monoxide vapor mixture is generated in an arc furnace 3 formed of a gas-tight steel shell 4 linedwith refractory carbon blocks` 5 and having a hearth 6 of broken coke. The furnace is heated electrically by arcs struck betweenv the hearth and graphite electrodes 1 which enter through water-cooled gas-tightglands not shown. Charge mixture isA fed in through an upper inlet 8 provided with gas-tight feeding means ynot illustrated. l Y n Y The-vapor mixture leaves the furnace through anarrow-throated orifice. 9 formed in asmall block' I0 of highlyv refractory material, such as boron carbide. The diameter of the orifice Qis ordinarily quite small, being usually only a few inches, even for very large furnaces. The orifice block IB is held by a carbon bushing I l in a socket in a carbon thrust-block I2 secured rin the furnace wall-and seated on a steel ring ,I3 welded to the furnace shell. Y i' The vapor mixtureliberatedin the furnace lead-magnesium alloy.`V 'I'he non-condensable carbon monoxide is continuously exhausted from beyond'the last st1eam I 6 through a stack Il` leading to a pump I8. Y Any solid depositiorming iin the vapor oricellmay be poked loose by an I Y. i break` upintoa rain 'of drops during their fall, are

alloy steel reamer I9 of diameter slightly less than that of the orice. This rod is mounted slidably opposite the orice in a gland 20 welded through a cover ange 2| on the end of the quench chamber. K

The lead-magnesium -quench alloyV is main-` tained under inert' gas -rirotecti-cn'in a closed im' sulated reservoir 22 provided with heat exchangers not shown for maintaining the alloy at a temperature below 650 C. This liquid is con-` tinuously forced by a pump 23 driven by a motor 24 through an insulated line 2,5 into a kdistributing box 26 mounted in the quench chamber t5I `above the path of the vapor issuing Afrom 'the orifice 9. In thebottom of the box 26, a vseries of Parallel elongated rectangular slots 23'! are cut in a direction perpendicular to the path 'of the magnesium vapor stream, these slots extending across almost the entire width Vof the quench chamber. The alloy delivered to the box 25 ows throughthe slots rl and falls freely across the issuing furnace vapor in the form of plateelike streams I6 of suiiicient thickness to constitute practically unbroken curtains of moving metal. These streams fall into a Collecting basin 2 8, which is formedI in the chamber l5 directly under the distributing .box 26 and below the path'of the furnace vapor stream, and are returned to the 'res-` ervoir 22 throughran insulated drain 2,8. Part of the quench liquid containing condensed magnesium is withdrawn continually from the reservoir by Va pump 3S driven by a motor (ilV and is circulated through a pipe 32 to a system, not shown, for distilling magnesium from the alloy, from which the magnesium-depleted liquid is Vre-v l turned for re-use bya pipe 33.

I In operation of the apparatus, the vapor 'stream ofvmagnesiuln and carbon monoxide issues from.

i. the orice 9 Vat considerable velocity,u`sually at least several hundred feet per second, and im-V pin'ges on the falling 'curtains I6 of 'quench alloy. The gaseous stream forces its way successively through each of the curtains in an extremely short period of time, and during such passage is thoroughly scrubbed `by the falling alloy.` The magnesium vapor is eiectively condensed and; absorbedrby the alloy, being thus separated from the carbon monoxide, which is exhausted through: the stack Vil. The enriched alloyireturns to the reservoir 22, from which it may be withdrawn to 'the'magnesium recovery step.

V.In the apparatus of the drawing, the slots 21 must be widev enough that the streams of quench liquid falling through them are suiiciently massive'that there is no tendency for them to become f discontinuous, i. e., to 'break upl into a shower" of discrete drops, under the action 'of the. im"-` pinging vapor stream.V 2in general, ar'slot width cf' at.KY least k0.75Y inch, and preferably 1.0 inch or re, is yrequired when the height of Vfree fall of the quench liquid is 2 or`3 feet. Y y 'l Y While, according to the invention.' the' quench liquid is preferably Vformed into massive plate-Y likeA streams byV means ofV slots, as illustrated, it

Vis also 'lpos'sribleto dispo'sethe `liquid inthe form or rod-like streali'is as by providing several series i 1 por -ls substantially all condensed, and continu- Y of Holes. instead lofwslots,v inthe bottom 4of theV Y distributing box 2S. ,'lhi'ese, rod-like'streams, which should .be of? diameter Vsuiicient. thatthey do not Y best spaced closely in staggered` v'array so that there isno possibility that the vaporst'rearn issuingfrom the furnace can und its way through theque'nc'h chamber without passing into inti-j mate 'contact with several of the liquid streams.

The impingement of a high-velocity stream of gas and vapor on continuous streams of flowing quench liquid in the manner of the invention offers ra number of advantages not shared by the streams from that of the furnace outlet. The

xed gas never tends to build up in the condenser, diluting the incoming vapor stream or blanketing it from 'effective contact with the quench liquid.

3. The surface of the quench streams is constantly renewed so that there is little local overheating or saturation offany part of the condensing area. Y

4. The Vstreams o`f 'quench yliquid present an ever'shifting sur'faceto the incoming gas. Chanheling cf the vapor stream thro-ugh the condenser, with consequent inefiiciency f gaseliquid contact and vloss of uncondensed vapor, does not occur to any degree.

5;'Inas'lnuch as the flowing 'streams of quench liquid are massive and continuous, in contrast to a spray or a rain of drops, there is little tendeiicy for 'entrapment 'qf the quench liquid in the exhaust gas. p

6. Practically all inner surfaces of the quench Vchamber areV constantly wetted by the ilowing liquid, 'so that foreign lparticles carrieduby the incomingvapor stream are 'washed away. Forma; tion of troublesome 'deposits is largely prevented.

As "a result of these and other considerations, excepticnallyihigh quenching eiiciencies are real` ized and operating qifcquliies are he'lqat a, mini# mum.

while trie iiiveiiiiqii has beeriqeseribeq 'vv'iiiiY particular reference to 'the 'manufacturejo'f-mag51 sium, it is equally applicable to the quenching of* sodium vapors 5in lead-sodium alloys.n Further,'so far v'as known, it may advantageously be 4.applied to the condeneatioh step of any metallurgical pC- ess in which a mixture of a re'ducible compound of a volatilizable -irletal and a reducing agent is heated io liberate metal vapor, Vwhich iiiiist then be Condell'Sdl.Y Still other applications of the in# liquid as a horizontal series of plate=likermassive streams fio'v'vihg vertically .fdo'wni/fard,in` free fall, causing the vapor mixture toimpinge hcrio'n tally.in-Sireqiiiform'qii die iiisij1iquiq-siieqiiicf the series and then'cqiq pass into"contact"withv each of lthe succeeding streams', whereby tligv;

ously withdrawing fixed VYgas beyond the last liquid j `strean'iiof the series. Y Y .g

2. Aprbqess according te claim 1 finw'iiicii the vquenqiiiiig liquid is a qiiiicuiily volatile riiq'lteii metal absorbent `for thevapoi".

. v3. A process 4,according to claim 1 in which metal vapor is magnesium land the quenching liquid is a'leadfi'nagrie'siu 2.17105'.

4. 'A process aceqrqiiigi'o claim 1 vin vvii'icii the metal vapor is sodium and the quenching liquid is a lead-sodium alloy.

5. A metallurgical process `which comprises:

heating a mixture of a reducible compound of` a volatilizable metal and a reducing agent to a temperature suiiicientto form metal vapor in a conned zone provided with a restricted outlet through which the liberated vapor issues as a horizontal stream, causing a quenching liquid for the metal vapor to flow vertically downward across the path of the issuing vapor stream in the form of a horizontally extending series of platelike massive streams flowing in free fall, whereby the metal vapor impinges on 'the `streams of quenching liquid and is condensed, withdrawing uncondensed gas from beyond the last of the liquid streams, and collecting the quenching liquid after its passage across the vapor stream and recovering metal therefrom.

6. Metallurgical apparatus for condensing metal vapor in a quenching liquid comprising, in

combination with a source of metal vapor and a reservoir for quenching liquid: a gas-liquid contact chamber in communication with Vthe vapor source through a restricted orice; a distributing box for quenching liquid mounted in thechamber above the-path of vapor issuing from the oriiice, the bottom of the box having therein a series of parallel slots disposed transversely to the path of the issuing vapors, each slot being sumciently wide that quench liquid falls therethrough as a plate-like massive stream; liquid collecting means for receiving liquid falling from the box mounted in the chamber under the distributing box and below the path of the vapor issuing from the oriiice; and circulating means for withdrawing liquid from the reservoir and supplying it to the distributing box and for with- 7*. Metallurgical apparatus` comprising: a metal-vapor generating 'furnace having a restricted vapor outlet; a quench condenser in communication with the furnace through the outlet; a source of quenching liquid;rv distributing means within the condenser for disposing the quenching liquid across the pathv of vapor issuing from the furnace outlet in the form of a horizontallyextending series of parallel plate-like massive streams, each flowing vertically downward; co1- lecting means within the condenser for receiving the streams of quench liquid; circulating means `for-conveying quenching liquid from its source to the distributing means and for returning it from the collecting means vto the source; and exhaust means for removing uncondensed gas from the quench chamber at a point on the opposite side of the` liquid streams from that of the fur# Y nace outlet.

THOMAS GRISWOLD, J R.

THOMAS H. MCCONICA, III.

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

' UNITED STATES PATENTS Date 121,752 British J an. 9, 1919

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