US2181148A

US2181148A - Process and apparatus for producing zinc

Info

Publication number: US2181148A
Application number: US169773A
Authority: US
Inventors: Melville F Perkins; Roland G Crane
Original assignee: American Smelting and Refining Co
Current assignee: American Smelting and Refining Co
Priority date: 1937-10-19
Filing date: 1937-10-19
Publication date: 1939-11-28
Anticipated expiration: 1956-11-28

Description

Nov. 28, 1939. M. F. PERKINS ET AL 2,131,148

PROCESS AND APPARATUS FOR PRODUCING ZINC Filed Oct. 19, 1937 3 Sheets-Sheet l INVENTORS MKII/Ille fer/(i115 l f ///l Bvbiand Crane Nov. 28, 1939.

M. F. PERKINS ETYAL PRQCESS AND APPARATUS FOR PRODUCING ZINC Filed ot. 19, 1937 s sheets-sheet 2 m Q07. M6,

Nov. 28, 1939.

' M. F. PERKINS ET Al.

A PROCESS AND APPARATUS FOR PRODUCING ZINC Filed Oct. 19, 1937 3 Sheets-Sheet 3 'Patented Nov. 2s, 1939 Melville F. Perkins and Roland G. Crane, Woodbridge, N. J., assignors to American Smelting and Refining Company, New York, N. Y., a corporation of New Jersey Application October 19, 1937, Serial N0. 169,773

15 Claims.

This invention relates to the art; of reducing oxidized ores or calcines of metals whose reduction temperatures exceed the boiling points of the particular metals. As zinc is the outstanding example of such a metal, the invention will be described with particular reference thereto.

It is lmown to produce zinc by introducing finely-divided zinc ore .pr calcine and carbonal c eous reducing agent into a retort maintained at 0 zinc reduction temperatures whereby the zinc content of the open, non-compacted charge isl reduced practically instantaneously in suspension to vapor, passing the zinc vapor and accompanying gases through a bed of incandescent coke to separate out the dust carried by the gases and toA convert any carbon dioxide to carbon monoxide, and treating the emerging vapors to recover the zinc content, e. g., by condensation. Such process is disclosed in United States Letters Patent No..

) 2,096,779 granted October 26, 1937 to George P.

Bartholomew and Edward P. Fleming.

The procedure just described may be aptly termed a ash reduction and the acceptable theory of operation divides the actual breduction i of the ore or calcine into two steps, the rst of which is expressed by the reaction ZnO+CO=Zn (gaseous) +CO2 f(l) and the second by the reaction C+CO2=2CO (2) Various data indicate that Reaction 1 proceeds much faster than does Reaction 2 so that for successful flash reduction, conditions must be such that Reaction 2 will proceed with sufcient speed to maintain an ample concentration of carbon monoxide in the reduction unit to permit reduction of substantially all of the zinc oxide in accordance with Reaction 1 before the particles pass from the reduction zone.` l A Among the various factors to be considered in the balancing' of conditions to assure the propery speed of Reaction 2 vfor maximum zincnreduction are y the height of 'the flash shaft, the temperature of the reductionzone of the ash' shaft,uthe degree ofpreheat of the charge, thev reactiven'ess' component "offthe "charge-2' tests show powdered charcoal to be twice as' re"` `4 active in the ash shaft 4as is" ordinarymetallurgical coke, thefratio of carbonItoorelr or 'calcine f able draft'through yth i dium, to prevent l such *The present4 inven Vpr'ovements inthel r of the carbonaceous in the charge," the degree of pulverization or sub#` division of ythe carbonaceous )component of the' charge, and the 'us-eof catalytic agents to speed the producer gas reaction-'t'ests'- show*k that *theffA addition'o'fsmau amounts of SOCIaLash,I say under (Cl.A 75-26) 1%, to the carbonaceous component of the charge increases the rate at which carbon dioxide is re. duced in accordance with Equation 2 and thus made available for the reduction of the zinc component of the charge in accordance with Equa- 5 tion 1.

From what has just been said, it Will be apparent that, viewed from the standpoint ofse' curing maximum eiiiciency in jthe zinc reduction I step, the zincky vapors withdrawn from the flash 1Q shaft and passed into the coke. filter should,` contain no appreciable amount of carbon dioxide,

Unfortunately however, the zinc vapor and carbon monoxide leavingthe ash column are' accompanied by suspended particles of carbon'jen- 1.5 trained in the vapors and the burden which this Q `places on the f|1tering"mediumfpresents a very i real obstacle to successful continuousv operation Y of the ash reduction unit as'awhole.:` Further, it is not practicabletogeliminate the id ust by inv.20'l creasing the size of thev particlesof `-ore 'orlrefduc ing fuel because of the 'adverse effecten redu..

may be mitigated byl using Ycoarser 'colre"fra ments, say kof, two-inch` `sizefthe' advantage i nullied by the detrimental 'eiect on 'condensation occasioned by suspensoidspassirigthr glifinto the condenser. 'f l In order, therefore, to Aalleviate the, influence'of thel dust, `it 'has been j'pr'op l continuously renew thefiltering ,medium M as byj" conning same as lan upright .jcolumnp anfd with; drawing coke from the bottom while 'adding addic. tional coke at the top)whilelpassing'the zincky vapors therethrough therebyfremov'inglr'thefsus pensoids from the vaporistreaiiif and ipmfventing clogging ofthe medium.:V While suchwpocfedure is wholly operable, it presciitsseveralfdis dvan- "ease ed .to iso;

a constanttemperature due,towjthyewA y i c continuous changing or renewalk ofthe medium itself, and the tendencyzfor aI por-tio fltheuzinc'@ corrective` measuregsuch "as provision apparatusv therefor"f"V which avoid clogging "prag use of a stationary coke bed with i'ts attendant advantages and at the same time maintaining the reduction and condensation operations at their respective maximum efficiencies.

In short the invention may be said to be largely based upon the discovery that improved results are obtained-when the vapors withdrawn from the flash reducer are subsequently treated,

not merely b'y a process of filtration, but, by'a very definite and positive process of conditioning basedupon oxidation of carbon to carbon monoxide by the producer gas reaction, CO2+C- 2CO, or otherwise.

Essentially this conditioning process consists in imparting to or establishing in the vapors an oxidizing gas content sufciently in stoichiometrical excess of the carbon in the particles entrained in the vapors to consume enough of the incandescent coke bed through which the vapors pass to render the bed self-cleaning thereby permitting the use, if desired, of a stationary coke bed with its many attendant advantages.

While it is preferred to employ carbon dioxide as the oxidizing gas, the conditioning process is not limited to its use. For example, air may be employed. Also, a choice exists as to the manner in which the requisite oxidizing gas content is supplied to the vapors. duced into the vapor stream as the latter emerges from the flash reducer with its burden of entrained particles; it may be introduced in the vicinity of the vapor entrance to the column or bed of incandescent coke and, particularly if carbon dioxide is the gas used, it may be established in the vapors before they leave the ash reducer by simple regulation of the ratio of powdered coke to ore charged to the flash reducer. shaft. In the latter case, care should be'exercised not to impair reduction efciency-if the residue at the bottom of the reducer shaft tends to become fusible or of a' slaggy nature, sufficient coarse-sized coke particles may be incorporated in the charge to maintain the residue in good condition for ready withdrawal from the shaft as a pulverulent material. However, the residue may be withdrawn as a slag, if desired. l

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out inthe claims appended hereto, the invention itself, as to its objects and advantages, and the manner in which it may be carried out, may be better understood by referring to the following description taken in connection with the acconpanyingdrawings forming a part thereof, in which- Fig. 1 is a view of a flash reduction unit according to the invention, the feeding mechanism and condenser being diagrammatically indicated and the remainder of the unit being shown in vertical section Fig. 2 is an enlarged view of a portion of the apparatus shown in Fig. 1;

Fig. 3 `is a cross-section taken on of Fig. 1;

Fig. 4 is a fragmentary sectional elevation of .a modification of the apparatus shown in Figs. 1-3;

Fig. 5 is a plan view of the feeding mechanism diagrammatically indicated in Fig. 1;

Fig. 6 is a sectional elevation taken on the line 6-6 of Fig. 5.

Like reference characters denote like parts in the une 3 3 A the several figures of the drawings.

Referring to the drawings,|0 represents generally the feeding mechanism for delivering the Thus, it may be intro- 'charge to theflash reducer |2 from which the vapors are conducted through coke chamber I4 to condenser I6.

Referring particularly to Figs. 5 and 6, the feeding mechanism |0 is shown comprising a hopper 20 leading into housing 22 in which is screw conveyor 24 driven by motor 26 via speed reducer 28. The housing 22. opens into heating chamber 30 dened by mufile 32 which is surrounded' by housing 34 defining combustion chamber 36 to which heat may be Supplied by fuel burners or4 electric heating means not shown. Heating chamber 30 is provided with a gas outlet 38 and a thermocouple tube 40 extends through muile 32 and housing 34 to the heating chamber 30. A pipe section 42 provided with fianged ends 44 and` 46 connects muflle 32 with elbow 48, the latter in turn being secured to and opening into refractory discharge tube 50. Elbow is provided with a sloping or tapered intake portion 52 above which is a rotative feeder 54 provided with blades or vanes 56, the feeder being driven by motor 58 via speed reducer 60. A punching or cleaning rod 62 with annular flange 64 is positioned at the top of elbow 48, the rod 62 passing through removable cap 66.

Referring now to Figs. 1, 2 and 3, the flash reducer I2 is shown comprising a vertically disposed column or shaft 10 of silicon carbide or other refractory material positioned ina combustion chamber 12 defined by heat insulating housing 14 surrounded by steel shell 16. A flue 18 is provided for the combustion chamber` 12 to which heat is supplied by burners l30 which are preferably arranged to open tangentially into the combustion chamber and thereby impart a whirling motion to the ames and hot combustion products around the tubular-shaft 10. Spaced supports 82 are provided for intermediately se' for carbon dioxide or other oxidizing gas leads to coke chamber I4, the latter in this case comprising a refractory column'- |00 positioned in a chamber |02 defined by a refractory housing |04 and heat insulation |06 and to which heat is supplied by burner |08 and hot gases from chamber 12 which pass around conduit 96 to chamber |02. A flue |09 is provided for chamber |02.

As clearly shownin Fig. 2,' the conduit 96 is joined to shaft 10 by a butt-joint ||0 while its other` end is received in a cradle |2 which holds it in registry with the -inlet port ||4 at the bottom of the column |00. 'I'he detail of the latter mounting is shown in Fig. 3. Opposite inlet port ||4 is an opening ||6 affording access to the bottom of the coke column, said opening being normally closed by plug ||8 which may be covered with removable cement or the like |20. An inclined grate |22 supports a bed of coke or other carboniferous material |24 in colurrm |00, the top of said column being sealed by refractory cover |26. Vapor conduit |28 leads from the top of column |00 to' condenser I6, an opening |30 normally closed by removable plug |32 being provided in the top of the column |00 opposite conduit |28. The coke chamber |4 and condenser 6 are shown supported independently of the flash reducer I2 by I-beams |34 and |36, respectively.

In the modication shown in Fig. 4, the reducer column is shown made up of refractory sections |38, the uppermost of which projects through an expansion slip-joint |40 into a header comprising a shell |42 and pipe |44 defining a combustion-chamber |46 and resting on.a base |41, which like the shell and pipe, is of suitable refractory material. The combustion space is continued around conduit 96 and coke column |00. Also in Fig. 4, one end of conduit 96 rests on the top of pipe |44, the `remaining space being bricked up and the conduit cemented in place while the other end engages a socket |48 on the bottom of the coke column.

In the coke column shown in Fig. 4, the sloping grate |22 of Figs. 1 and 2 has been replaced by a horizontal grate |50 which is positioned up in the column a substantial distance from the bottom and supported by a -body of refractory brick checkerwork |52. Suitable openings |54 and |56 which are normally closed by plugs |58 and |60, respectively, are provided.

Employing the apparatus hereinbefore described, the flash reduction process may be con` ducted as follows: a finely divided charge comprising a solid carbonaceous reducing agent and oxidized zinciferous material is fed to the hopper 20 from whence it passes by screw conveyor 24 iinto the muille 32 where it is preheated. 'I'hc charge may appropriately consist of ash roasted zinc calcine and coke dust with a majority of the particles minus 20D-mesh. With the present invention the amount of powdered coke or other carbonaceous material used in the charge may be varied within wide limits without impair-ing the eiciency of the operation.

The feeder 54 stirs up the charge and delivers it evenly to the tube 50 through which it drops by gravity into the reducer shaft 10 which has been previously brought to zinc reduction tem-- perature by the combustion of fuel supplied by burners 80. In shaft 10 the oxidized zinciferous material is reduceel practically instantaneously and zinc vapors together with the gaseous products of reaction, and suspensoidsl pass into refractory conduit 96.

It will be recalled that reduction of the zinc is accomplished by carbon monoxide according to Reaction 1` and that an ample concentration of carbonmonoxide is maintained according to Equation 2 by reason of the presence of carbon in the charge. Accordingly, if suflcient coke is used so that the vapors entering conduit 96 contain very little carbon dioxide, complete reduction is assured. However, the carbonaceous suspensoids entrained in'the vapor ifpermitted to remain as such would collect in the interstitial spaces of the non-moving coke in the coke column and prevent further flow of vapor through the coke thereby terminating the entire operation in a short time.

In accordance with the modification of the apparatus of the invention illustrated in Figs. 1

and 2, carbon dioxide or other oxidizing gasis introduced into conduit 96 through inlet 98 in an amount sufficient to convert the carbon ofthe entrained particles to carbon monoxide and toy plied toeo'lumn |00, intermittently as needed,-

through refractory cover |26. t

As previously brought. out thepresent invention alsocontemplates other methods of conditioning the vapor and operating the coke column as a reactor to maintain same continuously selfoperating by automatically keeping open the interstitial .spaces between the units of thecoke aggregate. 'Ihus a small amount ofair can lbe introduced at the base of the coke column and the entrained carbonaceous suspensoids in the vapors eliminated at that point. `Satisfactory results have been obtained in actual practise without the introduction of extraneous gas by simply supplying the vapors from the flash shaft itself to the conduit 96 with a suflicient carbon dioxide contentl to satisfy the necessary chemical reactions. The operation has been conducted in this manner so eflciently that less than 1% to 2% of the zinc content of the charge was found in the residues at the base of the ash shaft.

In passing from the ash shaft to the base of the coke column, the velocity of the vapors is somewhat diminished in the closure at the base of the coke column thereby allowing the coarser particles to settle and the reaction of the oxidizing gas upon the carbonaceous suspensoids to proceed. The vapors then pass through the grate.

|22 as shown in Figs. 1 or l2 or through the checker brickwork |52 as shown in Fig. 4 into the coke or reactor column, the baffles promoting turbulent gas flow, and retardation of the flight of any fine' suspensoids in the vapor stream..

Among the many advantages attending the use of the invention, the most important may be said to be the truly continuous and efcient operation of the esh reduction process which it provides. With the invention` it is possible to operate the process indefinitely without the shut-downs and costly delays which inevitably accompany choking or clogging of the coke bed and while the benefits are more pronounced when using a stationary -coke bed, it will be understood that the,

invention may be employed in conjunction with moving coke column.

While the invention has been described with reference to the productionof zinc, it will be apparent that it may be applied to the treatment of other artificial or natural oxidic ores where, as with zinc, the reduced metal is in the vapor state.

What is claimed is:

1. The process for treating oxidized zinciferous material which comprises charging such material and solid carboniferous material, both materials being in a ne state of subdivision, into a retort wherein the zinciferous material is reduced in suspension, passing the products of -reaction as a Stream to an incandescent carboniferous bed, supplyng an oxidizing gas to the stream in amount sucient to oxidize the carboniferous suspensoids entrained in said stream and render the carboniferous bed self-cleaning, passing the stream through said bed and recovering zinc from the gases emerging therefrom.

2. The process for treating oxidic ore of a metal requiring a temperature above its boiling point for successful reduction which comprises charging such .ore and a carbonaceous reducing agent to a substantially vertically-disposed retort maintained at a temperature conducive to reduction of the ore, both ore and reducing agent being introduced to the retort in a sufficiently ne state so that reduction is accomplished practically instantaneously in suspension, causing the products of reaction to flow as a stream to and through a bed of incandescent carbonaceous material, conditioning the stream with an oxidizing gas to consume carbonaceous suspensoids and render said bed self-cleaning, withdrawing the conditioned vapor from said bed and recovering metal from said vapor.

3. The process for treating oxidized zinciferous material Which comprises passing an intimate, finely-divided mixture of said zinciferous material and carboniferous reducing agent into a substantially vertically-disposed retort, effecting a substantially instantaneous reduction of the zinciferous material in suspension, passing the products of reaction as a vapor stream through an incandescent carboniferous bed, maintaining a substantial amount of carbon dioxide in the said vaporous reaction products, causing said carbon dioxide to react upon carboniferous suspensoids entrapped inthe vapor stream thereby enriching said stream in carbon monoxide, completing Athe reduction of residual carbon dioxide y to carbon monoxide in the carboniferous bed -thereby preventing choking of the said bed with suspensoids in the vapor stream, and condensing zinc from the vapors emerging from the said carboniferous bed. 'y

4. The process for treating oxidized zinciferous ores and calcines which comprises passing an intimate, finely-divided charge of such zinciferous material and carboniferous reducing agent into a substantially vertically-disposed retort and effecting substantially instantaneous vaporization of the zinc therein, providing a substantial amount of carbon dioxide in the vapor 'stream emerging from the retort, said carbon dioxide being in stoichiometrical excess of carbon entrained in the stream, producing a reaction between the carbon dioxide and carboniferous suspensoids in the vapor stream, said reaction being caused to proceed vintermediate the retort and a bed of incandescent coke to and through which the stream is next conducted, reducing in the coke bed any unreduced zinciferous suspensoids present in the vapor stream and also reducing to carbon monoxide any carbon dioxide remaining in said stream thereby rendering the coke bed self-cleaning and the zinciferous vapor stream substantially free from carbon dioxide and suspensoids, and condensing zinc from the thus puried vapor stream.

5. The process for producing zinc Awhich comprises passing an intimate, finely-divided mixture of oxidized zinciferous material and carboniferous reducing agent into a substantially vertically-disposed retort heated to a temperature conducive of zinc reduction, withdrawing the products of reaction from the retort as a vapor stream, establishing a substantial amount of carbon dioxidein said vapor stream, imparting turbulence of flow and heat for reaction to said vapor Ystream for a period sufiicing to reduce zinciferous suspensoids and carbonaceous sus- 'from the conditioned stream emerging from the carboniferous bed.

6. 'Ihe process for treating oxidized zinciferous material which comprises reducing same in suspension with such a kind and amount vof carbonaceous reducing agent as to impart a substantial content of carbon dioxide to the vapor Withdrawn from the reducer, passing the vapor to and through an incandescent bed of carbonaceous reducing agent, retarding the flow of vapor intermediate the reducer and bed sumciently to permit oxidation by the carbon dioxide of carbonaceous suspensoids entrained in the vapor and recovering zinc from the vapor which has passed through said bed.

7. In the process for producing zinc by flash reducing the zinc in a charge of oxidized ore or calcine and coke or other carboniferous reducing agent, passing the products of reaction through an incandescent bed of carboniferous reducing agent and recovering zinc from the emerging vapors, the improvements consisting `in utilizing suicient coarse coke in the charge to prevent slagging of the reduction residue and maintaining a carbon dioxide content in the products of reaction as same pass from the flash reducer to said incandescent bed that is in stoichiometrical excess of the carbon content of said products of reaction.

8. In the flash reduction of oxidized zinciferous materials with a carbonaceous reducing agent following which the vapors are conducted through a carboniferous bed maintained at a temperature above that at which the zinc would condense, that improvement which consists in conducting the reduction in such a manner that the zincky vapors withdrawn from the reducer contain a suflicient amount of carbon dioxide in stoichiometrical excess of carbon entrained in the vapors to render the carboniferous bed non-clogging and maintain it continuously open to the passage of vapors therethrough.

9. Apparatus for treating oxidized ores or calcines comprising the combination with a ash reduction shaft furnace, and a bed of carboniferous material, of means for conveying vapors from said furnace to said bed, and means for introducing gas into said vapors subsequent to their withdrawal from the reduction shaft but prior to their entrance into the carboniferous bed.

10. Apparatus for treating oxidized ores or calcines comprising the combination with a flash reduction retort, a confined bed of carbonaceous' material and a conduit connecting the vapor outlet of said retort to the vapor inlet of said bed, of means associated with said conduit intermediate the retort and bed retarding the ow of vapors before same enter said bed.

11. Apparatus for reducing finely divided oxidized ores and calcines and recovering metal therefrom comprising a vertically disposed retort, means for externally heating the retort to reduction temperatures, a closure, a duct interconnecting said retort and closure for leading gaseous materials from the retort to the said closure, a grate member in said closure supportiiow of gaseous reaction products from the retort to the bed, and

condensing instrumentalities interconnected with the said closure containing thebed for effecting condensation of the metallic components of the reaction products issuing from the said closure.

,1. 12. Apparatus for treating finely divided oxidized materials, such as oxidized zinciferous ores or calcines, comprising a vertically disposed retort, means for externally heating the retort, a closure, a duct interconnecting the retort and the bottom of .said closure for passing gaseous materials from the former to the latter, a grate in said closure adapted to support therein a bed of carboniferous material of considerable thickness at a' point substantially above the opening of said duct into the closure, means for externally heating the said bed, means defining a reaction chamber intermediate the retort and the bed, for 'retarding the velocity of gaseous reaction products owing from the retort to the bed, and condensing intrumentalities interconnected with the said closure containing the bed for 'effecting condensation of the metallic components of the reaction products issuing from the said closure. o

13. Apparatus for the reduction of oxidic ores and calcines comprising the combination with a vertically disposed retort and heating means therefor, of mechanism for feeding a finely divided 'charge to the retort, said mechanis'm comprising an enclosed conduit, means for introducing a charge of the material to be reduced into said conduit, means operating through said conduit for conveying the charge therethrough, heating instrumentalities in said conduit for preheating the charge as it is conveyed therethrough, V

v5 and means engaging the said charge as it emerges from said conduit andl uniformly feeding the charge into the retort.

14. Apparatus for reducing nely divided oxidized materials comprising thev combination with a substantially vertically disposed, externallyheated retort, lof feeding mechanism for introducing a charge of such material into the retort, said mechanism comprising a closed conduit, a hopper for delivering materials into said conduit, a screw conveyor operating in said conduit, heating means for the conduit for preheating the charge of materials being conveyed therethrough, feeding instrumentalities intermediate said screw conveyor and the retort for receiving the charge as it leaves the screw conveyor and uniformly feeding the charge into said retort without substantial cooling Aof the preheated charge and cleaning means for maintaining the entrance to the retort open.

15. Apparatus for `reducing finely divided oxidized ores and calcines comprising the combination with an externally heated, substantially vertically disposed retort, of feeding mechanism for the said retort for feeding a charge of materials uniformly therethrough, the said feeding mechanism comprising a closed conduit, a hopper for delivering a charge of materials into the conduit from a suitable source thereof, a screw conveyor operating in the conduit, an upwardly aring connecting the said conduit and the retort, a heating muiile in the said conduit for preheating the charge of material being conveyed therethrough, and a rotary feeding device in the upper part of the said aring, connecting delivery section for re ceiving preheated material from the screw conveyor and for uniformly feeding the said ma terial' into the said connecting delivery section and retort.

MELVILLE F. PERIUNS. IROLAND G. CRANE.

delivery section between A