US1914484A - Metallurgical furnace - Google Patents

Description

June 20, 1933.

E H. BUNCE ET AL METALLURGICAL FURNACE Filed Jan. 23, 1930 2 Sheets-Sheet l "a m3 Wk m Em M w A ATTORNEYS June 20, 1933 E. H. BUNCE ET AL. 914,434

METALLURGICAL FURNACE Filed Jan. 25, 1930 2 Sheets-Sheet 2 ATTORNEY Patented June 20, 1933 UNITED STATES PATENT OFFICE 1 EARL H. BUN OE AND GEORGE '1. MAHLER, 0F PALMEBTON, PENNSYLVANIA, ASSIGNORS TO THE NEW JERSEY ZINC COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY METALLURGICAL FURNACE .Appication filed January 23, 1930. Serial No. 422,768.

This invention relates to metallurgical furnaces and has for its object certain 1mprovements in metallurgical furnaces. The invention relates more particularly to metal lurgical furnaces employed in the metallurgy of zinc, 'such as zinc reduction furnaces.

According to the zinc reduction process outlined in our copending application, Serial No. 244,519, filed January 4, 1928, (which has since issued into United States Patent No. 1,749,127 of March 4, 1930), such contaminating metals as lead and the like may be effectively eliminated from zinc vapor liberated from charge materials by passing the vapor and retort gases through an appropriate eliminating medium. The practice more particularly contemplated in this copending application comprises the step of employing as the eliminatin medium agglomerated charge materials a out to be subjected to the reduction operation, the agglomerates being progressively passed downwardly through the eliminator and thence into and through the reduction retort, while the zinc vapor and retort gases rise upwardly and pass through the agglomerat-es confined within the eliminator. The agglomerates serve to filter out the undesirable lead, .leaving the resulting zinc vapor substantially pure.

In another of our copending appllcations, Serial No. 422,766, filed January 23, 1930, we have disclosed and claimed a metallurgical furnace adapted for the practice of the process of lead elimination just outlined. This latter application contemplates more particularly a vertically disposed eliminator mounted on a vertically disposed retort, the retort supporting the eliminator. The passageways of both the eliminator and retort are in substantial alignment with one another, so that the agglomerated charge materials introduced into the vapor end of the eliminator may be progressively passed downwardly through both the eliminator and retort by the action of gravity. In this manner the charge materials confined within the eliminator function as the eliminating medium.

Unusually good results may be obtained in the reduction of zinciferous materials containing lead and the like according to the process and apparatus more especially contemplated and disclosed in our aforementioned copending applications, but the eliminating medium will always consist, at least in large part, of charge materials about to be subjected to the reduction operation. This normally means that the charge materials are confined in a relatively long body or column, extending not only through the retort but also through the eliminator. In-

through the eliminator is governed by the rate of passage of the agglomerated charge materials through the retort. This also means that before the agglomerates have in fact reached the reduction zone in the retort they have been subjected to abrasion and dusting in the eliminator.

As a result of our investigations, we have determined that a metallurgical furnace may be constructed that overcomes in large part the objections just enumerated. This new apparatus is designed to avoid the necessity of employing as the eliminating medium materials that are subsequently to be subjected to the reduction operation. In fact, the charge materials may be alone subjected to a reduction operation, while a separate and distinct eliminating medium may be solely employed for the selective retention of the lead and the like from the zinc vapor obtained in the reduction retort.

The present invention contemplates a metallurgical furnace comprising a reduction chamber, and an eliminator communicating with the reduction chamber, said eliminator being provided with an inlet for the introduction and an outlet for the withdrawal of an eliminating medium.

The employment of an eliminator, in conjunction with a reduction chamber or retort through which an eliminating medium may be passed independent of the manner in which the reduction step proper is conducted offers a number of very desirable advantages: In the first place, a shorter column of charge materials may be subjected to the reduction operation; since the charge materials are not to function as an eliminating medium. Abrasion and dusting of the agglomerates are therefore reduced to a minimum before they are smelted. The lowermost agglomerates confinedizr-the-retort are subjected to much less overhead weight, than is the case when the upper section of the column of charge materials is employed as an eliminating medium.

An eliminating medium separate and distinct from the charge materials about to be subjected to the reduction operation offers other desirable features. It permits of the use of a medium perhaps better adapted to function as an eliminator than the charge materials. In any event the movement of the medium through the passageway of the eliminator may be regulated in accordance with the rate and efiiciency of the filtering action, rather than strictly with the rate at which the charge materials are progressively moved through the reduction retort. Furthermore, when employing an eliminating medium independent of the charge materials being fed to the reduction operation, its total volume and particle size may be adjusted to secure optimum filtering conditions. For example, the eliminating medium may advantageously consist of agglomerates or particles smaller in size than the agglomerates employed in the reduction retort.

In the practice of the present invention the independent eliminating medium'need not be placed above the reduction retort; it may advantageously be placed at a level no higher than that of the upper end of the retort. This feature is particularly desirable when the furnace building to be employed is otherwise not high enough readily to accommodate the retort with an eliminator placed above the same.

A separate and distinct eliminating medium also offers the advantage of being able to serve as a collector of valuable by-products, which may be separated and recovered by special treatment. Thus, the eliminating medium is adapted to collect lead, silver, etc. These metals may subsequently be recovered by treating suitably the medium in which they have gathered.

It is believed that these and other novel features of the present invention will be more fully understood by a consideration of the accompanying drawings, taken in conjunction with the following description, in which:

Fig. 1 is an elevation in section of an apparatus adapted for the practice of the invention; and

Fig. 2 is a modified form of apparatus illustrative of the invention.

The apparatus shown comprises a furnace structure 10 resting on concrete foundations 11. The furnace structure itself comprises a bottom 12, side walls 13, and an arched roof 15 of refractory material, such as heat resistant brick. An outer metallic casing 16 completely surrounds the furnace structure. The space between the arched roof and the top of the metallic casing is filled with suitable heat-insulating material 17, such as diatomaceous earth.

A central heating chamber 18 is defined by the furnace linings. Ports 19 are provided through the side walls of the furnace structure for the introduction of air and fuel to be burned within the heating chamber. These ports are adapted for the introduction of such fuel as pulverized coal, oil, gas, etc. In order effectively to heat the heating chamber and to regulate the operating temperature of the same, the ports are advantageously spaced throughout the height of the furnace structure. In the furnace shown one port is located at or near the bottom of the heating chamber, and a second port is located at or near the center of the chamber. An opening 20 is provided through a side wall of the furnace at or near the upper end of the heating chamber for the withdrawal of spent heating gases. This opening preferably connects with a stack or chimney (not shown). Other relatively small openings 21 are provided through the side walls of the furnace structure at various intervals throughout its height to take pyrometric temperature readings within the heating chamber.

A vertically disposed retort 14 is located within and centrally of the heating chamber. It may, for example, be constructed of suitable refractory material, such as heat-resistant brick of good-heat-conducting qualities. The lower end of the retort is supported by the bottom of the furnace structure. It is preferred that the retort be supported by the furnace structure at only one point, so that the retort may. expand and contract independent of the furnace structure; or, vice versa. This desirable result may be accomplished by supporting the retort only at its lower end.

A sleeve 22 is attached to the underside of the bottom of the furnace structure; its passageway being in substantial alignment with that of the retort. A revolving plaform 23, adapted to be moved about a vertical axis 24, is located immediately below the discharge end of the retort and sleeve. This platform is adapted to discharge spent residues 25 when the platform is revolved.

The upper end of the retort protrudes a convenient distanceabove the top of the main furnace structure. A conduit 26 connects with the retort near its upper end, which is adapted for the passage therethrough of zinc vapor and retort gases rising from the retort. A charging device 27 fits into the upper end of the retort, and extends downwardly within the same to a point preferably at a level slightly lower than the opening into the vapor discharge conduit. With the charging device extending downwardly such a distance, charge materials 28 may be kept out of the conduit. A removable cap 29 fits over the charging device. It may be removed from time to time for the introduction of fresh charge materials.

Suitable means are provided around the upper end of the retort for the regulation of temperature conditions within that end of the retort. Thus, an outer metallic casing 30 surrounds the upper end of the retort, at least in large part, providing a free space between the casing and the walls of the retort adapted to receive suitable heat-insulating material 31, such as coal dust. The size of the metallic casing may be varied in order to regulate the thickness of the layer of heatinsulating material. A door, or doors,32 is provided at or near the lower end of the metallic casing for the withdrawal of heatinsulating material, if that should become desirable. The upper end of the casing is preferably open so that heat-insulating material may be introduced or withdrawn.

An eliminator structure 33, which may advantageously rest on the top of the main furnace structure, adapted for the filtration of zinc vapor coming from the retort, is located immediately adjacent to the upper end of the retort. This device is adapted selectively to eliminate lead from the zinc vapor. The structure shown comprises what may be termed an eliminator 34, of substantial height. This eliminator may advantageously be constructed of heat resistant brick, such as employed in the construction of the retort. Its cross-sectional area and height may be varied to secure optimum eliminating conditions. The lower end of the eliminator connects with the zinc vapor discharge conduit coming from the upper end of the retort. This places the retort and the eliminator in free communication with one another. The lower end of the eliminator is preferably provided with means for discharging'eliminating medium 35. In the apparatus shown this means consists of an opening 36 and a door 37 in connection therewith. Thus, the eliminating medium may be shoveled out of the hole from time to time as desired, While the operator stands on a convenient Working platform 39. Particularly if zinc metal is to be produced, the door should be appropriately sealed to prevent the seepage of objectionable amounts of air into the eliminator.

Referring more particularly to Fig. 1, a vapor discharge conduit 39 connects with the eliminator at or near its upper end, and leads into a ZlIlC vapor treatment device 40. This zinc vapor treatment device consists of a condenser, if the zinc vapor is to be condensed to zinc metal. If, on the other hand, zinc oxlde is to be manufactured, the device is adapted for the oxidation of the zinc vapor. If zinc dust is to be manufactured, the device consists of acanister adapted to effect the condensation of the incoming zinc vapor into minute particles of zinc.

A charging device 41 fits into and extends a convenient distance downwardly in the passageway of the eliminator. The lower end of the device preferably extends at least slightly below the level of the vapor discharge conduit, so that the eliminating medi-' um may be kept therefrom. A removable cap 42 fits over the charging device; it may be removed from time to time for the introduction of fresh eliminating material.

An outer metallic casing 43 is suitably spaced from and surrounds, at least in large part, the eliminator. The space provided between the casing and the eliminator is filled with suitable heat-insulating material 44, such as coal dust. The size of the casing may be varied in order to regulate the thickness of the layer of heat-insulating material. A door, or doors, 45 at or near the bottom of the eliminator structure is provided in the metallic casing for the withdrawal of heat-- insulating material, if that should be desirable.

In the case of the apparatus shown in Fig. 1, the furnace structure is located adjacent to the upper end of the retort, but it extends upwardly beyond the upper end of the retort. Such an arrangement causes the vapor and gases coming from the retort to pursue a generally upward direction, while progressing through the eliminator.

In the case of the modified form of apparatus shown in Fig. 2, however, the eliminator extends downwardly below the upper end of the retort. This result isobtained by locating the main part of the eliminator structure alongside of the furnace structure. Such an arrangement causes the vapor and gases coming from the retort to pursue a re verse direction from that taken while in the retort.

In the modified form of apparatus shown in Fig. 2, the eliminator structure 46 rests upon a supporting and working platform 47. As in the case of the apparatus shown in Fig. 1, this furnace structure comprises an eliminator 48, preferably constructed of refractory material, such as heat-resistant brick. An outer and spaced metallic casing 49 encompasses the eliminator as far as possible. The space provided between the casing and the retort is filled-with a layer of suitable heat-insulating material 50, such as coal dust. A door, or doors, 51 is provided in the metallic casing at or near its lower end for the withdrawal of heat-insulating material, if that should become desirable. A charging device 52 fits into and extends downwardly in the eliminator a convenient distance, preferably at a level at or slightly lower than the opening in the vapor discharge conduit that connects the eliminator with the retort, so that eliminating medium 53 cannot clog the conduit. A removable cap 54 fits over the charging device.

The lower section of the eliminator is provided with a door 55 for the removal of fouled eliminating medium. This door, particularly in the case of the manufacture of zinc metal, should be carefull sealed to avoid any substantial seepage 0 outside air into the eliminator. A discharge conduit 56 connects with the eliminator at or near its lower end. This conduit in turn joins with a zinc vapor treatment device 57.

If reference will again be made to Fig. 2, it will be seen that a dry joint 58, substantially zinc-vapor-tight, is provided at or near the upper end of the retort, which maybe regarded as dividing the retort proper from the extension or prolongation of the same into which fresh charge materials are introduced. This joint is placed below the-point at which the vapor conduit connects with the retort. With a construction of this type, any movement of the vapor conduit (caused for example by the movement of the eliminator and/or zine vapor treatment device) will not deleteriously be translated to the walls of the retort. Any suitable joint may be thus employed to protect the retort. For example, a telescoping joint could advantageously be employed.

Numerous modifications of the above described apparatus may be employed in the practice of the invention. Thus, it will be apparent that the eliminator may be placed in an inclined position, through which the eliminating medium may nevertheless be progressively moved. Various devices may also be employed for the removal of fouled eliminating medium, etc.

For the eliminating medium itself, various suitable materials may be employed. Thus, the eliminating medium may be composed of any appropriate material that will withstand the prevailing temperatures employed, and which will not react with or contaminate the metallic zinc vapor so as to affeet the subsequent treatment of the zinc vapor to manufacture whatever zinc products are desired.v The eliminating medium may, for example, be composed of graphite, charcoal, coal, coke, or other suitable carbonaceous material, clay refractories. silica refractories. alumina refractories, silicon carbide, partially crushed zinc ore, residues and the like. Moreover, these materials may be employed in anv desired quantity, and with any desired particle size.

Optimum elimination of lead from the zinc vapor is obtained when the eliminating medium provides a multiplicity of tortuous paths for the flow therethrough of the zinc vapor and retort gases. In order to permit the free passage of the zinc vapor and gases through the eliminating medium, the eliminating material should be sufficiently porous for that purpose. These conditions are satisfactorily obtained when the eliminating medium is composed of aggregates. Moreover, the movement of the vapor and gases is made more uniform if the aggregates are approximately uniform in size, so that the porosity of the eliminating medium as a whole may be substantially uniform.

The above described apparatus may be employed as follows in the reduction of zinciferous material, in which the resulting zinc vapor is contaminated with objectionable amounts of lead and the like.

The cap 29 is removed and an appropriately agglomerated charge of mixed zinciferous material and carbonaceous reducing agent 28 is introduced into the charging device 27. The agglomerates are gradually introduced until the passageway of the vertically disposed retort 21 is filled. The cap 29 is then returned.

Suitable fuel and air, to form highly heated combustion gases, are introduced through the ports 19. The heating gases circulate around the retort within the heating chamber 18, and ultimately find their way out of the opening 20, which communicates with a stack or chimney (not shown). Pyrometric readings are taken from time to time through the openings 2]. in order to determine temperature conditions within the heating chamber. \Vhen necessary, suitable adjustments are made in the amounts of heating gases or fuel introduced through the ports 19 to obtain temperature conditions for optimum reduction operations.

As the heating gases circulate within the heating chamber, heat is gradually driven through the walls of the retort and into the agglomerated charge materials confined therein. When the heating operation has proceeded to the point where reduction of the zinc compounds present in the charge materials is effected, zinc vapor is liberated and retort gases are evolved. In the preferred use of the apparatus, the operation is conducted in such manner as to obtain a stack or chimney draft within the retort. This draft effect tends to cause the liberated zinc vapor and retort gases to rise upwardly. Controlled amounts of gases, such as air, may advantageously be admitted into the lower end of the retort.

As reduction of the zinc compounds present in the charge confined in the lower end of the retort proceeds to completion, the revolving platform 23 is setin motion, and spent residues 25 are discharged from the retort. The removal of these spent residues in turn causesthe upper column of agglomerates confined within the retort to settle downwardly. thus causing the agglomerates to pursue a progressive movement downwardly through the passageway of the retort. As spent residues are removd, fresh charge materials are introduced into the upper end of the retort.

In case it is desired to conduct the reduction operation substantially continuously, the cap 29 may be removed and connection made with a source adapted to feed fresh charge materials into the charging device 27 as fast as spent residues are removed from the bottom of the retort. Under certain operating conditions the platform may be made to revolve continuously at a speed adapted to discharge spent agglomerates as fast as the reduction step proceeds to completion.

The mixture of liberated zinc vapor and retort gases rises upwardly within the retort among the agglomerates. and ultimately finds its way through the vapor discharge conduit 26' into the eliminator 34 (see Fig. 1). Due to the natural buoyancy of the hot vapor and gases. combined with the stack dratt mentioned above, the vapor and gases wend their way upwardly among the pieces of eliminating medium 35, ultimately to find their way through the discharge conduit into the zin'c 'vapor treatment device 40. The eliminating medium is preferably present in the eliminator in the form of agglomerates 01 substantially the same size. As the zinc vapor contac s with the pieces of eliminating medium. the lead present in the zinc vapor is selectively retained, while the substantially lead-free zinc vapor passes toward the zinc vapor treatment device.

If it is desired to renew the eliminating medium from time to time. as when the eliminating material becomes fouled with undue amounts of retained lead and the like. fouled eliminating medium may be removed, as desired. from time to time by opening the door 37 and drawing the material through the opening 36. At the same time fresh elimin ating material may be introduced into the eliminator by removing the cap 42 and introducing the material into the charging device 41.

In order to eliminate lead from the zinc vapor rising through the eliminator, the temperature of the eliminating medium must be carefully regulated. The temperature of the eliminating medium may be suitably regulated by controlling the rate of dissipation of heat from the hot medium. It will, of course, be apparent that the eliminating medium is heated by the hot zinc vapor and retort gases from the retort. If the eliminating medium is too hot and it is desired to cool the same, heat-insulating material 44 in suitable amounts may be withdrawn from the door 45. On the other hand, if heat is dissipating too rapidly and it is desired to have the eliminator at a higher temperature, additional heat-insulating material may be provided within the metallic casin 43. v

The lead is eliminated from the zlnc vapor most effectively when the rising stream of vapor and gases is made to traverse a relatively long path. This may be accomplished by employing an eliminator of substantial height or length, as well as by a regulation of the size of the agglomerates of the medium.

When practicing the process of lead elimination in the apparatus shown, zinc vapor contaminated with lead enters the eliminator at the bottom, and substantially lead-free zinc vapor is withdrawn from the eliminator at or near its upper end.

From the foregoing 'description of the process of lead elimination that may be practiced in the apparatus of Fig. 1, it will be clear how a similar process may be practiced in the apparatus of Fig. 2. llnstead of moving upwardly through the eliminator, the zinc vapor (and retort gases) passes downwardly through the eliminator of Fig. 2. The action of filtering out the lead is the same in both instances.

Apparatus such as that described above is particularly useful in the elimination of lead, silver and the like from zinc vapor when it is desired to keep the eliminating medium out of contact with the actual reduction or smelting step. In other words, the eliminating medium may be worked entirely independent of the charge materials employed in the reduction retort.

We claim:

1. A zinc metallurgical furnace comprising an externally heated reduction chamber provided with an inlet for the introduction of charge materials and an outlet for the withdrawal of spent residues, and a heat insulated eliminator removed from but in communication with said reduction chamber so that zinc vapor and retort gases may pass from the chamber to the eliminator, and a zinc vapor treatment device in association with the eliminator to receive lead-free zinc vapor, said eliminator being provided with an inlet for the introduction of an eliminating medium and an outlet for the withdrawal of fouled elminating medium completely from the system.

2. A zinc metallurgical furnace comprising an externally heated vertically disposed reduction retort open at both ends, a vertically disposed heat insulated eliminator, the eliminator being removed from and positioned exteriorly of the retort, a conduit connecting the retort at or near its upper end and the eliminator'at or near one end adapted for the passage therethrough of zinc vapor and retort gases, said eliminator being provided with an inlet for the introduction of an eliminating medium and an outlet for the withdrawal of fouled eliminating medium, and a zinc vapor treatment device in association with the eliminator to receive lead-free zinc vapor.

3. A zinc metallurgical furnace comprising an externally heated vertically disposed reduction retort, a vertically disposed eliminator provided with means for regulating the temperature thereof, the eliminator being removed from and positioned exteriorly of the retort, a conduit connecting the retort at or near its upper end and the eliminator at or near one end adapted for the passage therethrough of zinc vapor and retort gases, said eliminator being provided with an inlet for the introduction of an eliminating medium and an outlet for the withdrawal of fouled eliminating medium, and a zinc vapor treatment device in association with the eliminator to receive lead-free zinc vapor.

4. A zinc metallurgical furnace comprising a vertically disposed and externally heated reduction retort adapted for the passage of charge materials therethrough by the action of gravity, a vertically disposed and heat-insulated eliminator adapted for the passage of an eliminating medium therethrough by the action of gravit the eliminator being removed from an positioned exteriorly of the retort, said eliminator being located at or near the upper end of the retort, a conduit connecting the retort at or near its upper end and the eliminator at or near one end adapted for the passage therethrough of zinc vapor and retort gases, and

a zinc vapor treatment device in association with the eliminator to receive the lead-free zinc vapor.

5. A zinc metallurgical furnace comprising an externally heated reduction chamber provided with a vapor outlet, an upright heat insulated eliminator in communication with the vapor outlet of the reduction chamber, the eliminator being removed from and positioned exteriorly of the reducing chamber to insure better dissipation of heat therefrom, said eliminator being provided with an opening at its upper end for the introduction of fresh eliminating medium and an outlet at its lower end for the complete withdrawal of fouled eliminating medium from the entire system and a zinc vapor treatment device in association with the eliminator to receive lead-free zinc vapor.

6. A zinc metallurgical furnace comprising an upright externally heated reduction retort open at both 'ends. the upper end of said retort being adapted for the introduction of charge materials and the lower end of said retort being adapted for the withdrawal of spent residues, a vapor and gas outlet near the upper end of said retort, and an upright heat insulated eliminator in communication with said reduction retort at its vapor and gas outlet, a vapor and gas outlet near the upper end of the eliminator, said eliminator being provided with an opening at its upper end for the introduction of fresh eliminating medium and an outlet at its lower end for the complete withdrawal of fouled eliminating medium from the entire system, and a zinc vapor treatment device in association with the eliminator to receive lead-free zinc vapor.

7. A zinc metallurgical furnace comprising an upright externally heated reduction retort open at both ends, the upper end of said retort being adapted for the introduction of charge materials and the lower end of said retort being adapted for the withdrawal of spent residues, a vapor and gas outlet near the upper end of said retort, a joint being provided in the retort below the vapor and gas outlet so that movement of the outlet conduit is not injuriously translated to the retort below, and an upri ht heat insulated eliminator in communication with said reduction retort at its vapor and gas outlet, a vapor and gas outlet near the upper end 01'' the eliminator, said eliminator being provided with an opening at its upper end for the introduction of fresh eliminating medium and an outlet at its lower end for the complete withdrawal of fouled eliminating medium from the entire system.

8. A zinc metallurgical furnace comprising an upright externally heated reduction retort open at both ends, the upper end of said retort being adapted for the introduction of charge materials and the lower end of said retort being adapted for-the withdrawal of spent residues, a vapor and gas outlet near the upper end of said retort, a oint being provided in the retort below the vapor and gas outlet so that movement of the outlet conduit is not injuriously translated to the retort below.

9. A zinc metallurgical furnace compris- 1ng an exteriorly heated vertically disposed reduction retort with an opening at or near its upper end for the introductionof charge materials and an opening at or near its bottom for the withdrawal of spent residues, a vertically disposed heat-insulated lead elim- -inating device in open communication with the retort at or near its upper end adapted for the passage therethrough ,of liberated zinc vaporand retort gases coming from the retort, the lead eliminating device being removed from and positioned exteriorly of the reduction retort and its accompanying furnace structure to obtain better dissipation of heat, said lead eliminating device being provided with an inlet at or near its upper end ing to claim 9, in which the upper of the retort communicates with the lower end of the lead eliminator.

12. A zinc metallurgical furnace comprising a reduction chamber provided with an inlet for the introduction of charge materials and an outlet for the withdrawal of solid spent residues, a lead eliminatin chamber in association with but positionec l exteriorly from said reduction retort and its accompanying furnace structure, said lead eliminating chamber and said reduction chamber communicating with one another by means of a connecting conduit so that evolved gases and liberated zinc vapor may pass freely from the reduction chamber into the lead eliminating device, said lead eliminating chamber likewise being provided with an opening for the introduction of fresh lead eliminating material and an opening for the withdrawal of fouled eliminating material completely from the system, and a zinc-vapor treatment device in association with said lead eliminating chamber, said zinc-vapor treatment device and lead eliminating chamber communicating with one another by means of a connecting conduit so that evolved gases and lead-free zinc vapor may pass freely from the lead eliminating chamber into the zinc-vapor treatment device.

13. A zine metallurgical furnace according to the preceding claim, in which the lead eliminating device issupported by the furnace structure surrounding the reduction chamber.

In testimony whereof we aflix our signatures.

EARL H. BUNCE. GEORGE T. MAHLER.

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