US1994347A - Purifying zinc - Google Patents

Description

March 12, 1935; p M GlNDERy l 1,994,347

PURIFYING ZINC Filed Deo. 20, 1932 A 4 Sheets-Sheet 1 A #a mfmymmww ATTORNEYS March l2, 1935. P. M. GINDER l PURIFYING ZINC Filed Dec. 20, .1932

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ATTORNEYS March 12, 1935. P. M. GINDER PURIFYING ZINC Filed Deo. 2o, .1932

4 Sheets-Sheet 3 INVENTOR F/f/L /P M. 6711/557? ATTORNEYS P. M. GINDER PURIFYING ZINC Filed DSG. 20, 1932 March' 12, 1935.

4 Sheets-Sheet 4 INVENTOR P/f/L /P M G/NDV? ATTORNEY-S atented Mar.. 12, 1935 l'STATES T FFICE PURIFYING ZINC Philip M. Ginder, Palmerton,

New Jersey Zinc Company, corporation of New Jersey Pa., assignor to The New York, N. Y., a

Application December 20, 1932, Serial No. 648,056

7 Claims.

points than zinc. The apparatus of the invention is particularly adapted for purifying zinc by the action of a reflux column as described in the copendng application for Letters Patent of the United States of Leon S. Holstein and Philip M. Ginder, Serial No. 540,566, filed May 28, 1931. Throughout this specification and the appended claims, I have used the term reflux column to define a column or tower in which ascending metallic v'apor moves in contact with descending (refluxing) molten metal resulting from condensation of ascending vapor; a substantial amount of refluxing molten metal being permitted to ow out of the base of the column and metallic vapor e reaching the top of the column being appropriately recovered.

The methodv disclosed in this application is claimed in application Serial No. 671,315, filed May 16, 1933.

The apparatus of the invention comprises a plurality of retorts for distilling zinc metal operatively associated with a plurality of reux col.- umns. Preferably, each retort is provided with a reflux column. The communicating means between a retort and its associated column permits the ow of vapor from the retort to the lower end of the column and the counter-currentflow' of refluxed molten metal from the column to the retort. Each reflux column has an outlet near `its upper end communicating with means for co1- lecting and/or condensing purified zinc, preferably common to all or a plurality of the columns. The purified molten zinc flows into a reservoir or sump from which it is removed and cast into slabs or otherwise appropriately disposed of.

The invention will be best understood from a consideration of the accompanying drawings, in which Fig. 1 is a sectional end elevation of tus embodying the invention,

Fig. 2 is a top plan, partly in section, of the apparatus,

Fig. 3 Vis a side elevation, partly in section, of the apparatus, and

`Figs. 4 to 12 show modified forms of the reflux column.

The apparatus illustrated in Figs. 1, 2 and 3 of the drawings comprises an elongated furnace structure l0 having a central longitudinal partition 11 dividing the interior of the furnace into two adjacent and communicating heating chaman appara.-

bers or laboratories 12. Ahorizontal row of zinc distillation retorts 13 is arranged in each heating chamber 12. The two horizontal rows of retorts are set back to back against the central wall 11 and are mounted at a slight inclination from the rear or back toward the front where they extend through appropriate openings in the two side or vfront walls of the furnace structure. The retorts 13 are made of suitable refractory material, such for example as silicon carbide. The furnace construction, mounting of the retorts therein and the firing of the furnace with fuel gas in conjunction with a recuperator may advantageously follow in general the practice of the conventional Belgian spelter retort furnace.

The outer end of each of the retorts 13 is connected vby an elbow 14 (of fire clay or the like) to the bottom of a reflux column. Each reflux column comprises a cylinder 15, of fire clay or other appropriate refractory material, having an openingin the bottom thereof registering and communicating with the upper end of the elbow 14. The top of the cylinder 15 is closed by a plate 16 appropriately luted with mud or the like to prevent the escape or zinc vapor. The cylinder 15 is surrounded by appropriate heat insulatingmate- 4rial 17 (such as refuse zinc oxide) confined in place by a steel jacket 18 supported in its operative position in front of the furnace in any appropriete manner.

A transverse perforated plate 19 is arranged within the cylinder 15 a short distance above theI bottom thereof, and serves to support a column of sized illing material 20. The filling material may advantageously be coke crushed to about inch, or any other inert packing material such as crushed refractory, fire-clay brick etc.

One end of an elbow pipe 21 communicates with the top of the cylinder 15 approximate or slightly above the upper level of the filling material 20 therein. The other end of the elbow pipe 21 communicates with a downcomer 22 mounted on and communicating with a closed trough or conduit 23. The conduit 23 extends along the entire side of the furnace and is mounted at a slight inclination vtowards a molten metal sump or collecting pot 24 of relatively large capacity arranged at one nace structure. Since the conduit 23 slopes downward across the front of the furnace, the downcomers 22 are progressively longer from the end of the furnace remote from the collecting pot to the end adjacent the collecting pot. Each downcomer 22 has a clean-out opening immediately above the conduit cover 38 normally end of the furclosed by a brick 25 or the like. The downcomers 22 communicate with the conduit 23 through apertures 39 in the conduit cover 38. Each aperture may be closed by inserting a slide damper in place of the brick 25 to prevent the escape of zinc vapor from the conduit when cleaning or changing retorts or reflux columns. The e1- bow pipe 21, the downcomer 22 land the conduit 23 may be made of silicon carbide or the like. The conduit 23 is supported by a sheet metal trough 27 lined internally with appropriate refractory material, such for example as tamped loam or clay 26. Sufficient heat radiation is provided for condensing all of the zinc vapor entering the conduit to molten metal. The trough 27, as Well as the reflux columns, are supported by a suitable framework or brackets 37 secured to the buckstays of the furnace.

'Ihe collecting pot is provided with heating means, such as a burner 28 for fuel gas (e. g. carbon monoxide). The heating gases from the burner 28 pass over the surface of the purified zinc metal in the collecting pot and escape through a stack 29, thus maintaining the zinc metal in a uniform molten condition. Each of the two conduits 23 (on opposite sides of the furnace structure) delivers molten metal to a well 30 at one side of the collecting pot 24. The wells 3G communicate with the collecting pot be- 10W the level of the molten metal in the latter, so

v that products of combustion in the collecting pot cannot enter the condensing system. Above the Well 30 a. tube 31 extends vertically upward from the conduit 23. The vertical tube 31 is of such height and is so constructed as to insure substantially complete condensation to molten zinc of such residual zinc vapor as may find its way into the tube. The collecting pot 24 has a dipping well 32 from which molten metal may be removed as desired for casting and the like.

Each retort 13 is provided with a charging well 33 communicating with the retort through an e1- bOw pipe 34. Molten zinc metal to be purified is poured from a charging ladle 35 into a trough 36 discharging into the well 33.

In the operation of the apparatus shown in Figs. 1, 2 and 3 of the drawings, the vapor evolved from the baths of boiling zinc metal in the retorts 13 passes through the elbows 14 'into the associated reux columns. The zinc vapor is Purified with respect to lead by refluxing and/or rectification in the reflux or rectifying columns 10. The resulting purified zinc vapor passes out of the reflux columns, through the elbow pipes 21, and is condensed to molten zinc in the downcomers 22 and the conduit 23. The purified molten zinc ows ldown the conduit, on either side of the furnace, into the wells 30 and thence to the collecting pot 24, from which it is ladled out as desired from the dipping well 32.

Molten zinc metal (of the grade to be refined) is charged from time to time (or continuously if desired) into each operating retort (through the troughs 36 and wells 33) to maintain an approximately uniform volume of molten metal in each retort. A certain proportion (say around 10 to 30%) of the zinc vapor entering each reiiux column is ultimately returned to its associated retort as molten metal in consequence of the refluxing action. This refiuxed molten metal contains the lead removed from the zinc vapor, and its return to the retort results in progressively increasing the lead contentof the molten metal therein. Each retort is continuously operated until the lead content of the molten metal therein has progressively increased to such a high percentage that the vapor delivered by its associated reflux column to the condensing system has as high a lead content as can be tolerated in the condensing system. Such a retort is then cut out of operation, is cleaned of the lead-high metal therein, and is then recharged with molten zinc metal of the grade undergoing purification.

Starting with the initial charging of a retort with zinc metal of the grade to be purified, the lead content of the molten metal in the retort gradually increases in consequence of distillation and the reuxing action, and consequently the lead content of the purified zinc vapor delivered to the condensing'system from this retort correspondingly increases. In other words, zinc vapor of the highest purity is delivered to the condensing system from an initially or freshly charged retort and the purity of the zinc vapor delivered to the condensing system progressively decreases as the retort continues in operation with periodic charging but without cleaning. In the apparatus of the invention, a continuously uniform puried zinc metal is obtained by combining or blending the zinc vapor from a plurality of retorts in different stages of the working-olf period between a freshly or initially charged retort and the cleaning out of the retort when the lead content of the molten metal therein attains a predetermined maximum value. In practice, this result is brought about by cleaning out and freshly charging the retorts in sequence' over the working-off period. Thus, with a furnace of 24 retorts (12 on each side), and a working ofi` period of 8 days, three retorts are cleaned and freshly charged each day. Furthermore, the delivery of the blended condensed metal (from the reflux columns of a plurality of distillation retorts containing molten metal of progressively varying lead content) to a relatively large 'pool of molten metal tends further to a uniforming of the purified product ladled or otherwise Withdrawn from the collecting pot 24.

The following specific example of the practice of the invention is illustrative and in no sense restrictive or limiting of its scope or application. The furnace contains twenty-eight retorts, fourteen on each side, of the spelter retort type, approximately 5 feet long and 7-10 inches internal diameter (oval section). The re clay' cylinder 15 of the reflux column is 2 ft. 3 in. high and '7l/2 in. internal diameter, with a wall thickness of l in. The steel casing 18 is 121/2.in diameter and the annular space between the cylinder and casing is'filed with refuse zinc oxide. The zinc metal to be p'uried averaged .06% lead. Approximately 2400 pounds of metal were volatilized per day of 24 hours, in each retort, of which approximately 20% was condensed in the reux colunm and returned to the retort as molten metal. The furnace as a whole thus produced about 26.9 tons of purifiedzinc metal per day, which was Withimediately preceding its cleaning out approxi mately .006%. The remaining retorts delivered to the condensing system Zinc vapor of progressively varying intermediate lead content depending upon their respective stages'or relative positions inthe working cycle of continuous retort operation. From 15-18 tons of puried molten metal were maintained in the collecting pot 24.

The construction ofV reflux column illustrated in Figs.` 1, 2 and 3 is simple, inexpensive and gives very satisfactory results in practice. Various modications may be made in the construction of the reflux column. Several such modifications are indicated in Figs. 4 to 12 of the accompanying drawings. In the modification illustrated in Fig. 4, the reux column consistsV of a stack of pots 40 of re clay, silicon carbide or equivalent refractory material. The pots 40 are rectangular in form with side walls 41 beveled in such fashion that the pots can be stacked oneabove the" other. The bottom of each pot has a transverse slot or opening 42 approximate one end thereof. The upper surface of the bottom or" each pot is provided with transverse ribs 43, parallel to the slot 42; the ribs being of progressively increasing height from the end nearest the slot to the end furthest from the slot. The pots 40 are stacked.

in staggered relationship so that the bottoms therof form 'a column of superposed horizontal baiiies through which metallic vapor ascends and molten metal descends in zig-zag paths. The ribs 34 serve to retain shallow pools of molten metal on the bottoms of the pots. The cascade effect of molten metal pouring over the ribs facilitates intimate contact between the ascending vapor and the descending molten metal. The top of the reilux column is closed by a plate or cover 44 through which extends an oi-take pipe 45 leading to the downcomer 22 of the condensing system. The'assembly of stacked pots 40 is heat insulated in any appropriate manner, as for example by refuse zinc oxide 1'? confined in place by a steel casing 18.

Fig. illustrates a reux column without lling or packing material. The reflux column consists of a tube 46 of re clay or like refractory material surrounded by heat insulation 17 held in place by a steel shell 18. Such a column without filling or packing .material must be made relatively high and narrow in order to secure adequate purication of the zinc vapor by refluxing and/or by rectification.

In Fig. 6, the refractory cylinder 15 of the reux column is packed. or lled with spheres or balls 47 of refractory material, which function in a manner analogous to the sized packing of coke hereinbefore described. A

The reux column of. Figs. '1, 8 and 9 is provided with spaced and superimposed baffles 48 in the form of saucer plates. The saucer plates are circular with a segment cutaway and have a'recessed bottom or upper surface for retaining shallow pools of molten metal thereon. Three pins 49 depend from the lower side of each saucer plate and serve to support land properly space the superimposed plates. The saucer plates are arranged with their cut away segment staggered to provide a tortuous or zig-zag path for the countercurrently owing vapor and molten metal. With a reflux column of this type,.in a run vof seven days continuous operation, there was obtained a purified zinc metal product containing less than 0.002% lead, from a high lead zinc containing up to'1.0% lead. The molten metal in the distilling retort contained 20% lead after the seven days of continuous operation.

Fig. illustrates a reflux column of annular cross section provided by a hollow cylindrical core 50 and a concentrically spaced outer cylinder 51.

The core member 50 is closed at its bottom to provide a receptacle for insulating material 52, such as dust coal or the like. The core member is attached to and suspended from an annular plate 53 closing the top of the annular refluxcolumn. The depth of insulating material in the core member may be varied to provide 4the required degree of heat insulation, and a cooling medium, such as air, may be circulated through the unillled length of the core member.

The reflux column of Figs. 1l and 12 is in the form of a bubbling tower. Each of the four bubbling stages or devices in this tower or column comprises a transversely disposed annular lower plate 54 having an upwardly extending central cylindrical collar 55. A transversely positioned cap 56 having a depending peripheral edge is positioned over the collar in appropriately spaced relation therewith. The plates 54 and caps 56 have depending pins 57 and 58, respectively, which serve to support and properly space the superimposed members. During the operation of the reux column, each annular plate 54 supports a bath of condensed metal. Overow pipes 59 provide communication between the superposed baths of molten metal and permit condensed metal to reux back into the retort. The lowermost overflow pipe 59' has an upwardly bent lower end to retain therein a seal or trap of molten metal which prevents the ascent of vapor through the pipe. The ascending metallic vapor bubbles under the peripheral edge of the caps 56 through the baths of condensed metal on the plates 54. The condensed molten metal ows'down the pipes 59 from one metal bath to the next and nally returns (reuxes) to the zinc distillation retort 13.

In each of the reflux columns hereinbefore described, it is preferable to so arrange the heat insulation 1'7 around the reuxJ-or rectifying column that the zone or region at which the greater part of the heat escapes from the column is the top. In such case the top of the column functions as a dephlegmator.

Various modications may be made in the apparatus herein particularly illustrated and described without departing from the spirit of the invention. Thus the reflux columns may be equipped with charging devices for feeding molten metal to be rened at or near their tops; molten metal so charged replacing, in whole or in part, molten metal charged directly into the retorts, as hereinbefore described. Other types of retortsmay be used for volatilizing the impure zinc to be rened. Thus, the impure metal may be volatilized in a crucible equipped with internal electric resistors; or an externally heated builtup retort may be used instead of the specic type of retort hereinbefore described.

I claim: Y

1. An apparatus for purifying zinc comprising a plurality of zinc distillation retorts, reflux columns communicating at their lower ends with said retorts, means permitting the ilow of vapor from each retort tothe lower end of its associated reux column and the countercurrent ow of molten metal from the reflux vcolumn to the retort. an inclined conduit with which the upper ervoir arranged toreceive molten metal from the lower end of said conduit, and an upright pipe open at its top and communicating at its bottom with the lower end of said conduit.

2. An apparatus for purifying zinc comprising a plurality of zinc distillation retorts, a re- 'ux column operatively associated with each of said retorts, an inclined conduit for condensing zinc vapor, communicating-,means between the top of each reux column and said conduit, and means for closing each of' said communicating means and thereby operatively disconnecting the reflux column from the conduit.

3. An apparatus for purifying zinc comprising a plurality of zinc distillation retorts, a reflux column operatively associated with each of said retorts, a common condensing system operatively associated with the upper ends of said reflux columns, a reservoir operatively associated with said condensing system, and means for supplying extraneous heat to said reservoir.

4:. yAn apparatus for purifying zinc comprising a. plurality of zinc distillation retorts, a reflux column operatively associated with each of said retorts, means for conveying puried vapor from said rei'lux columns to an inclined conduit for condensing the vapor, a collecting Well for receiving molten metal from the lower end of said conduit, a reservoir communicating with said collecting Well beneath the normal molten metal level therein, and means for supplying hot combustion gases directly upon the molten metal in said reservoir.

5. An apparatus for purifying zinc comprising a plurality of zinc distillation retorts, a reiiux column operatively associated with each of said will the communication between any downcomer and the conduit, a reservoir for receiving molten metal from the lower end of said conduit, and means for supplying extraneous heat to said reservoir.

6. An apparatus for purifying zinc comprising a plurality of zinc distillation retorts mounted"v in a heatingchamber, separate zinc charging means connected to each retort at the ends thereof, a vertically disposed reflux column for each retort, separate conduits connecting the bases of each reiiux column to the ends of the retorts adjacent the zinc charging means, a commonconduit for collecting purified metal in communication with the upper end of each of said reux columns, and a molten metal sump communicating with said conduit.

7. An apparatus for purifying zinc vapor comprising a plurality of zinc distillation retorts mounted in a heating chamber, a plurality of reilux columns each of which is separately connected with an individual retort, zinc charging means connected to a nd of each retort, separate conduits connectedlto each retort adjacent its zinc charging means and connected to the respective reux column, means for conveying puried zinc from said reflux columns to a common condensing system and a reservoir connected with said condensing system and adapted to receive and hold `a relatively large accumulated bath of molten metal condensed in said condensing system.

' PHILIP M. GIN'DER.

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