US2478594A - Method of condensing zinc - Google Patents

Description

9, 1949- A. 1.. J. QU-ENEAU 2,478,594

METHOD OF CONDENSING ZINC Filed Aug. 15, 1947 INVENTQR v AUGUSTIN L. J. QUENEAU ATTORNEY Patented Aug. 9, 1949 'F-UN IT ED STATES PATENT QFFICE METHOD OFICONDENSVING Augustin L. J. QueneaugMorristownf'N. sappucauennugusus, 1947., s erislgndrzeseca r .l This invention relates to the recovery of :zinc from its ores, and more; particularly to improvementsin the method of and apparatus for condensing 'zinc vaporiromthe furnace in whichithe ore is smelted. V

The-gases and vapors iwhichr are released .in the smelting of carry large uantities of both sensible and latent heat. The temperature of the gases and vapors isofthe orderiof .950-.1 000 Cu. and the zincis-in the form of :vapor from which the latentheatof nanorizationmustbe withdrawn inorder to effect the =condensation. The metal must also be cooled to :the desired temperature. Thus, one of the-majorproblemsoi-the zinc industry ,ior .many years has beenthe ,eificient condensation of zinc vapors and the separation of the zinc from the inert gases such as nitrogen and -.carbon monoxide -.Which accompany th zinc vapors.

,It is the object ,of the present invention to provide a simple, efiective and economical method of condensing andseparatingzinc from the smelter gases and vapors. i

vAnother object oi the invention is the provision of apparatus in'which the method may be conducted in an economical and ,efficient manner.

Other objects and advantages .of the invention mourns; ((31.375-38) will be apparent as it .is .better understood by reference to the iollowing specification and the accompanying drawing, which illustrates diagrammatically an apparatus adapted to permit accomplishment of the stated objects.

The invention depends upon the use oimolten zinc as a .coolantfor the gases and vapors released from the smelting iurnace, and the circulation of large uantities of such molten .z-inc ior that P rpose, In carrying-out the invention, molten zinc from ,a holding-furnace is circulated continuously to and Home condenser in which thezinc is. distributed in dispersed form for maximum contact with the gases and vapors .which are cooled rapidly .irom the high temperature at which they enter the condenser to a temperature of about 500-525 C, and in-anyevent to .a temperature above-the ireezing point .ofzinc, 420 C.

(Diving to thepressure exertedby the gases and vapors from the smc1ting iurnace, for example about ,five pounds ,persquar-e inch, the inert or fixed gases, nitrogen, carbon monoxide, -etc., are forced through the pool of molten zincriat the bottom of the.condenseras-bubbles, thus assuring condensation; of any remaining zinc vapor. These gases -,eventua1;ly leave the molten zinc which flows into the holding iurnace. ;The gases may be treated 'thereaiter to recoverianyvz nc 1 2 oxide, blue powder or the like. The latter can be returnedior reprocessing and introduction to thesmelting furnace tocecover "the zinc content;

The gases, free from zinc products, .may be compressed and :used1.for-any,desirable purpose, or discarded to "the .atrnosphere. :The zinc collected in the ,holding :iurnace is recirculated andirom time to time the excess resulting from condensation-of the zinc-vaporis pumped. from the furnace and cast ,or ,molded. r r

The procedure as rbriefly 'outlined ensures the maximum recovery of .zi-nc vapors as metallic zinc andthe minimum of zinc-oxide, blue powder and the like. The moltenzzinc is readily maintained and circulated to act as a coolant in the condenser, and is themost zemcient coolant tor that purpose. ,All of the zinc content of the furnace gases and vapors is eventually recovered. The operation is eilicient and economical, and a substantial improvement in the methods heretofore available. I

The procedure will be better understoodby reference to theaaccompanying drawing, in which '5 indicates a smelting furnace, for example a blast furnace adapted --to be su-pplied with a dry blast of oxygen-enrichedair througha-pipe 6 connected to tuyres- I. Astheresult of the=smelting operation, gases andvapors are delivered through a pipe 8 at .a temperature in the "neighborhood of 950 1000 C. It is desirable to maintain the gases at this temperature to :avoid the possibility of areversible reaction in which carbon monoxide isbroken down into carbon dioxide and carbon. The presence of carbon dioxide is undesirable, since it reacts with zinc to produce zinc oxide and carbon monoxide. r

The pipeB deliversthei -gases an'd vapors to a condenser!) consisting of asteel shell lined with a suitable :refractorymaterial such as carborundum, carbon or graphite. The pipe 8 issimilarly lined, The condenser is provided with manholes closed by covers ill and H to permit inspection .of the interior of the condenser. Within the condenser, a block 12 of graphite is provided with a central opening l3 and a -plur-ality of upwardly directed passages Id. "The central opening 13 is connected by "a Pipe .45 of graphite or similar material to a pump 16 submerged in molten zinc in a holding jfurnace 1.1. The pump 16 may be constructed of graphite :orlike material in accordance with thedisclosure -of:my application Ser.

No. 757,404, filed June 27,1947. The pump 16 permits the circulation of molten zinc from the holding furnace through the pipe 15 to the distributor 12. Thus the, moltenvzinc is delivered to the condenser 9 in dispersed form, that is in a spray or rain of fine particles which fall through the atmosphere of the condenser and wash the walls thereof. The molten zinc is thus brought into intimate contact with the gases and vapors entering through the pipe 8, and the zinc vapors are rapidly condensed and cooled to the desired temperature, that is, preferably between 500 and 525 C.

Since there is a large amount of surplus heat, water is sprayed continuously on the wall of the condenser by means of a plurality of pipes l8 in.

quantity suificlent to maintain satisfactory temperature conditions in the condenser.

A large pool of molten zinc I9 accumulates in the bottom of the condenser. This pool is suflioient in amount to fill a connection 20 between the upwardly-directed le 9 and a second upwardly-directed leg 2| of the condenser, and extends upward into the leg 2|, where the molten zinc is supported by the pressure of the gases within the condenser. The connection 20 is cooled by sprays of water directed thereon through pipes .22. The connection 20 and leg 2! are preferably lined with the same material used as a lining for the condenser 9. Such material has a high heat conductivity, thus permitting energetic cooling by the water sprays.

A pipe 23 of graphite or similar material is connected to the leg 2| and to a downwardly extending pipe 24. The molten zinc which accumulates in the condenser 9 is forced over by the pressure of the gases into the pipes 23 and 24, and thus is delivered to the pool of molten zinc 25 in the holding furnace H. A refractory cover 26 is provided on the end of the pipe 23 to permit inspection of the interior of the pipe through the manhole in a wall of the holding furnace I! which is normally closed by a cover 21. A pump 28, similar to the pump [6, is connected to a pipe 28 of graphite or similar material, through which the molten zinc can be withdrawn from time to time and delivered to a mold or casting machine 30.

A pipe 3| extends above the pipe 23 and above the level indicated at 32 is preferably lined with firebrick in order to conserve the heat in the molten zinc which splashes upwardly during the evolution of the gases therefrom. Above the pipe 3!, a pipe 33 extends upwardly. It need not be lined, becaus at this level the temperature of the gases has dropped to 400 C. or less. A pipe 34 delivers the gases to a wet scrubber 35, preferably of the Theisen or Bian type, in which any remaining zinc vapor is separated from the gases in the form of blue powder or zinc oxide. This material, together with the water used in the scrubber, is delivered through a pipe 36 to a settler 37 in which the zinc oxide and blue powder collect. The surplus water is withdrawn through a pipe 38 to a collector 39 and may be re-used.

The gases, freed from practically all of the zincproducts, are delivered through a pipe 4!] to a baghouse 4! which may be of the usual type, preferably with shaking mechanism for the bags. Any remaining zinc oxide or blue powder is filtered from the gases and collected. This material, together with the solids from the settler 3i, may be reprocessed and returned to the smelting furnace in order to recover the zinc content.

The gases escape through a pipe 42 and, being still at a relatively high temperature, are passed through an exchanger 43 which is cooled by water supplied through pipes 44. After cooling, the gases are delivered by a pipe 45 to a compressor 46 and thence through a pipe 41 to a gas holder 43. The gases may be withdrawn as required through a pipe 49 for use, or they may be discharged to the atmosphere.

In starting the operation, it is necessary to have the zinc in the holding furnace in a molten condition and also to maintain the pipe l5 at a proper temperature. A burner EE! is disposed in the wall of the holding furnace l1 and is adapted to burn oil, gas or other material in order to raise the temperature of the furnace to the desired point. An electric heating coil 5| may be disposed about the pipe [5 externally of the furnace i1 so that the pipe is sufiiciently heated to prevent freezing of the molten zinc therein.

In the operation of the device, it is necessary to circulate relatively large quantities of molten zinc at a temperature preferably between 500 and 525 C. The rate of circulation should be 10-30 times the hourly production of zinc vapor in the smelting furnace. Thus, if the blast furnace rate of production is two and one-half tons of zinc vapor per hour, the molten zinc injected into the condenser would besupplied at a rate varying between 25 and '75 tons per hour, the quantity varying with the temperature and relative proportions of zinc vapor and gases issuing from the furnace.

The zinc holding furnace may have a capacity of -150 tons in order to supply the required metal for circulation through the condenser. The incoming gases, after dropping the zinc vapor as a result of contact with the dispersed molten zinc, are forced to bubble through the molten zinc in the pool at the bottom of the condenser and in the legs 2!] and 2 I. The circulating zinc and the condensed zinc pass through the vertical leg 2| in a series of surges or spurts, under suificient positive pressure to overcome the head of molten zinc in the leg 2 I. The length of this leg is such that the zinc rises to a point where it overfiows through the pipe 23 into the holding furnace.

The uncondensed gases, substantially zinc-free with the exception of zinc vapor saturating these gases at their temperature-and pressure, continue upwardly for treatment in the scrubber and baghouse as hereinbefore described.

Various changes may be made in the procedure as described and in the apparatus employed therein without departing from the invention or sacrificing the advantages thereof.

I claim:

1. The method of condensing zinc from gases and vapors produced in a smelting furnace which comprises spraying molten zinc in finely-divided form into the upper portion of one leg of a condenser having two upwardly-directed legs connected at their lower portions from a spray nozzle positioned in the upper portion of said one leg, introducing the gases and vapors from the furnace into said one leg of the condenser for intimate contact with the molten zinc sprayed therein with resultant condensation of zinc from said vapors, maintaining a sufficient body of molten zinc in the lower portion of the condenser to maintain the connection between the two legs thereof full of molten zinc, maintaining the gases and vapors in said one leg of the condenser under a pressure sufficient to force molten zinc of said body upwardly into the other leg of the condenser and to force gases and vapors from which zinc was condensed through said connection and upwardly through the molten zinc in said other leg, removing the gases passing'upwardly through the'molten zinc in said other leg from said other leg, recovering the residue of zinc oxide and blue powder from said removed gases, and withdrawing molten zinc from the condenser.

2. The method of condensing zinc from gases and vapors as set forth in claim 1 in which the gases and vapors in said one leg of the condenser are maintained under a, pressure of about 5 pounds per square inch.

3. The method of condensing zinc from gases and vapors as set forth in claim 1 in which the molten zinc sprayed into the upper portion of said one leg of the condenser is at a temperature of from about 500 C. to 525 C.

4. The method of condensing zinc from gases and vapors as set forth in claim 3 in which the temperature of the gases and vapors introduced into said one leg of the condenser is between about 950 C. and 1000 C.

5. The method of condensing zinc from gases and vapors as set forth in claim 1 in which molten zinc withdrawn from the condenser is recirculated and is sprayed into the upper portion of said one leg of the condenser.

6. The method of condensing zinc from gases and vapors as set forth in claim 1 in which the molten zinc sprayed into the upper portion of 6 said one leg of the condenser is at a temperature from about 500 C. to 525 C. and the gases and vapors in said one leg or the condenser are maintained under a pressure of about 5 pounds per square inch.

'7. The method of condensing zinc from gases and vapors as set forth in claim 6 in which the temperature of the gases and vapors introduced into said one leg of the condenser is between about 950 C. and 1000 C.

AUGUSTIN L. J. QUENEAU.

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

UNITED STATES PATENTS Number Name Date 1,966,627 Johannsen et a1. July 17, 1934 2,070,101 Weaton et al. Feb. 9, 1937 2,208,586 Kemmer July 23, 1940 2,238,819 Neve Apr. 15, 1941 2,348,194 Crane et a1. May 9, 1944 2,381,403 Chisholm Aug. 7, 1945 2,381,405 Griswold. Jr. Aug. '7, 1945

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