US2457548A - Process for condensing zinc vapor - Google Patents

Description

Dec. 28, 1948. E. c. HANDWERK ETAL 2,457,548

PRO'CS'S FOR CONDENSING ZINC VAPOR Filed June 22, 1946 ATTO R N EYS Patenlneliv Dec. 28, 1948 PROCESS FOR CONDENSING ZINC VAPOR Erwin C. Handwerk and George T. Mahler, Palmerton, Pa., assignors to The New Jersey Zinc Company, New York, N. Y., a corporation of New Jersey Application June 22, 1946, Serial No. .678,540

(Cl. 'I5-88) 2- Claims. 1

This invention relates to condensing zinc vapor, and has for its object an improved method thereof.

In the customary pyrometallurgical practices of smelting zinc ores. the zinc is recovered as molten metal by condensing the zinc vapor contained in the gaseous products of the smelting operation. In continuously operated smelting equipment, such as modern externally heated retorts or electro-thermally heated retorts, lthe zinc vapor diluted with ordinary smelting gases, such as carbon monoxide and the like, is passed througha condenser in which an operating temperature 1s maintained for effective condensation of the zinc vapor to molten zinc. This temperature may advantageously be of the order of from 500 to 550 C. Since the gas frequently enters thecondenser at a temperature at least 300 C. higher than the proper operating temperature, it is customary in such cases to thermally associate with the condenser suitable heat-disslpating means for maintaining the proper temperature, and especially is this so with zinc smelting equipment of relatively large capacity. In the copending patent application of ourselves and Harry C. Haupt, Serial No. 626,508, filed November 3, 1945, there is disclosed a splash zinc condenser in which the heat-dissipating means for the condensing chamber are cooling jackets thermally associated with the outside walls of the chamber, and in a companion application Ser. No. 633,004, led December 5, 1945, we described the positioning of positive artificial cooling means within the condensing chamber itself.

A characteristic feature of the splash condenser described in the aforementioned applications is the provision of a substantial volume of molten zinc in the bottom of the condensing chamber, which is kept under continuous agitation and which communicates with another body of molten zinc in a discharge well exterior of the condensing chamber. While investigating the performance of this splash condenser under commercial operating conditions, we have discovered that it is possible to maintain a proper operating temperature within the condensing chamber by appropriate dissipation of heat from the body of molten metal in the discharge well. Thus, by direct artificial cooling of the molten metal in the discharge well, we have found that suiticient heat can be withdrawn from the communicating body of molten zinc in the condensing chamber Ato maintain the proper operating temperature of the chamber.

Thus, the method of the present invention comprises -passing a gaseous stream containing zinc Vapor through a condensing chamber having a body of molten zinc therein, maintaining exteriorly of the chamber a body of molten zinc communicating with the molten zinc in the chamber, and controlling the operating temperature of the condensing chamber by subjecting the exterior and communicating body of molten zinc l to direct artificial cooling while facilitating cirthe molten zinc therein, or in the condensing chamber, to maintain the proper operating temperature of the chamber. The cooling of the exterior and communicating body of molten zinc is advantageously effected by a stream of extraneous cooling medium flowing through a confined path in said molten zinc but out of direct contact therewith. Intimate contact between the zinc vapor bearing gaseous stream and the molten zinc within thev condensing chamber is eiected by hurling molten zinc from said body thereof upwardly into the upper portion of the chamber through which the gaseous stream passes.

The foregoing and other novel features of the invention will be best understood from the following description taken in conjunction with the accompanying drawing, which illustrates, by way of example, a condenser in which the invention may advantageously be practiced, and in which- Fig. 1 is a longitudinal sectional elevation of the condenser, and

Fig. 2 is a top plan view of the condenser.

The condenser illustrated in the drawing is of the splash type described in the aforementioned applications, to which reference is made for a fuller description of such features of construction as are not directly concerned with the present invention and hence not herein illustrated and described. As shown in the drawing, the condenser comprises a generally rectangular condensing chamber 5 having a zinc vapor inlet 6 approximate one end and an exhaust or waste gas outlet 'l approximate its other end, and is lined with suitable refractory material. The zinc vapor inlet 6 is connected by a pipe 8 to a source of zinc vapor, such as a vertical zinc smelting retort. The zinc vapor inlet 6 and the gas outlet l'are shielded by depending refractory bafiies`9 tom of the well l2. Any other and I0, respectively. to prevent splashing o`r spraying of molten zinc into the inlet or outlet.

The condensing chamber communicates, be-k neath the lower edge of its end wall I i, with a discharge well i2 having an overilow spout I3 determining the level a of the body of molten zinc in the collecting chamber. A collecting trough I4 receives the molten metal overflowing the spout I3 and conveys it to casting equipment or the like. The lower portion of the end wall II dips into the molten metal between the condensing chamber and the communicating discharge well and seals the condensing chamber from the atmosphere at this point. The overflow spout I3 and trough I4 may be dispensed with, and molten metal manually dipped or otherwise suitably removed from the well I2 for casting, storage or other purpose. As zinc vapor condenses in the chamber 5, the resulting molten zinc collects in the body of molten zinc in the chamber, yand molten zinc is removed from the well I2 by continuous overflow, by dipping at periodic intervals, or in any other suitable mannerto maintain, for all practical purposes, a substantially constant volume of molten zinc in the chamber.

A generally cylindrical rotor I5vis mounted within the condensing chamber 5. The rotor is carried by a hollow or axially bored metal shaft I 6 mounted in bearings outside the condenser. The shaft I6 is horizontally disposed and extends through the side walls of the condensing cham-` ber between the zinc inlet and the gas outlet in al direction generally transverse to the direction of gas ow through the chamber. The rotor may be constructed of graphite, silicon carbide or other suitable refractory, and is separated from direct contact with the shaft I6 by a sleeve I8 of instream of gas containing zinc vapor enters the condensing chamber beneath the baille 9 of the inlet 6, and iloWs in a generally horizontal direction through the chamber and beneath the baille I to the exhaust gas outlet l. Where the entering gas is derived from a vertical retort smelting operation, it will have a temperature of around 820-900" C., and will generally contain around 30 to 50% zinc vapor diluted for the most part with carbon monoxide gas. The rotor I is rotated at a relatively high speed, say around 100 to v150 R. P. M., clockwise as viewed in Fig. 1, so that the pockets 2| in rapid succession pick up and throw sheets or showers of molten zinc into the gas stream. The upwardly-directed and rapidly succeeding sheets or showers of molten metal splash into th'e shower or rain of molten metal particles falling through the chamber, and also splash against the baille 9 and the roof of the condensing chamber, with the result that the condensing chamber is substantially filled with sheet-likey showers and moving particles of molten zinc which form ideal nuclei for the condensation and subsequent coalescence of the zinc vapor.

The rotor I5 agitates the body of molten zinc in the bottom of the condensing chamberand the molten metal is hence in constant motion. The

temperature of this body. of molten zinc may be, for all practical purposes, taken as the operating temperature of the condensing chamber and hence of the condenser itself. In accordance with the invention, this body of molten zinc is mainsulating cement. The shaft I6 has a plurality of..

circumferentially spaced peripheral ribs I 9 embedded in the cement sleeve, and the bore of the rotor has a plurality of spaced recesses filled with the cement of the sleeve, so that the shaft. sleeve and rotor are eiectively keyed together. The shaft I6 is cooled by the iiow of a cooling medium, such as water, through its axial bore.

The peripheral surface of the rotor I5 has a plurality of circumferentially spaced-pockets or` cups 2|. The pockets have a generally scoop-like section with a relatively long advancing flat section and a shallow semi-circular depression at the inner end or bottom of the pocket. The shaft I6 is positioned at a level substantially above that.

of the molten zinc adapted to be held in the chamber 5, and the rotor I5 is of such outside diameter that its lowermost pocket is beneath the` molten zinc level a. The shaft I6 (and hence the rotor I5) is driven by an electric motor or other suitable source of power (not shown).

Artificial cooling means are operatively associated with the discharge well I2 to cool the body i of molten zinc therein. While the artificial cooling means may be of any suitable type, satisfactory results are secured with a bayonet watercooler depending from a suitable support or resting on the refractory floor or bottom of the well. As illustrated in the drawing, a metallic (e. g. iron) cooling shell 22 of substantial width and having water inlet and outlet pipes 23 and 2l, respectively, is operatively supported by a frame A25 and depends into and substantially to the botliquid may be circulated through stead of water.

suitable cooling i the shell 22 intained at the contemplated operating temperature by the dissipation or withdrawal of heat therefrom into the artificially cooled body of molten zinc in the discharge well. Thus, circulation of the cooling medium in the cooling shell 22 abstracts heat from the molten zinc in the well and as a consequence heat is withdrawn from the communicating molten zinc in the condensing chamber. Due to its agitated condition and its inherent good heat conductivity, the molten zinc in the condensing chamber readily gives up its heat to the artificially cooled communicating molten zinc in the discharge well. By properly controlling the artificial cooling applied to the molten zinc in the well, heat is withdrawn or dissipated from the molten zinc in the condensing chamber in such amount and at such a rate as to maintainthe proper operating temperature of the condenser, e. g. 500 to 550 C. At this operating temperature, 'substantially all of the zinc vapor is condensed, the condensed molten zinc is collected in the body of molten zinc in the condensing chamber, and molten zinc is withdrawn from the chamber into the discharge well.

In the practice of the invention in the con- 'I'he artificial cooling to which the molten zinc in the Well I2 is subjected is advantageously regulated by varying the submerged area of the cooling shell 22. This may be done manually by lifting or lowering. the shell, or by varying its inclination. Since the operating temperature of the condenser is indicated by the temperature of the molten zinc in the condensing chamber, the articial cooling may advantageously be regulated by that temperature as. obtained from a suitably positioned pyrometer or other temperature measuring instrument. .Due to the agitation of the molten zinc in the condensing chamber, the molten zinc in the communicating well is in constant circulation and when the slight operating temperature differential between the two bodies of molten zinc for a particular condenser has been ascertained, the articial cooling may be regulated by the temperature of the molten zinc in the well. The artificial cooling may be automatically adjusted in response to temperature changes of the molten zinc in either thef condensing chamber or well. Thus, as shown in the drawing, the submerged area of the cooling shell 22 is automatically regulated by a temperatureresponsive actuating means 26 operatively connected to a pyrometer 21 positioned in the molten zinc in the well I 2. If the temperature of the molten zinc in the well rises, the actuating means 26, responding to that temperature rise, lowers the shell 22, thereby increasing its submerged area and hence its cooling effect. If, on the other hand, the temperature of the molten zinc decreases, the actuating means 26 raises the shell 22 and thereby decreases its cooling effect. In

this manner, the temperature of the molten zinc, in the well is maintained within predetermined limits by regulating the cooling effect of the shell 22, and thereby the operating temperature of the condensing chamber is controlled. As previouslystated, the pyrometer 21 may be positioned in the molten zinc in the condensing chamber, although it is generally more convenient and equally satisfactory to position it in the molten zinc in the well.

Molten zinc may be manually or otherwise dipped from the discharge well I2, instead of overflowing the spout I 3 into the trough I4. Dipping is generally carried out at periodic but frequent intervals, and only such an amount of molten zinc is removed from the Well at each dipping as to maintain, for practical purposes, a substantially constant volume of moltenzinc in the condensing chamber. A certain minimum volume of molten zinc should be maintained in the well in order to-provide an adequate heat reservoir for withdrawing heat from the condensing chamber and dissipating such heat through the articial cooling means as well as to prevent freezing during such interruptions in condenser operation as occasionally occur in practice, and the depth of molten zinc in the well should be suillcient to permit adequate immersion of the cooling means. In practice, heat is dissipated from the molten zinc in the well at about the same rate that heat is withdrawn from the condensing chamber, and the molten zinc in the well is hence not unduly cooled. While the relative volumes of molten zinc in the condensing chamber and discharge well will depend upon the size and capacity of the condenser, and perhaps to a lesser degree upon the effectiveness of the agitation of the molten zinc in the chamber, the following example is indicative of these factors:

The condenser was of the splash type illustrated in the drawing and had a condensing capacity of about 6 tons of zinc per day of 24 hours. About 2000-2500 pounds of molten zinc was main\ tained in the condensing chamber and about 500 pounds in the discharge well, and the area of communication between the two bodies of molten zinc was of the order of one-half square foot. 'I'he rotor I5 lifted about 5000 pounds of molten zinc per minute. In' other words, molten zinc in amount approximately equivalent to the body thereof in the condensing chamber was lifted from that body and thrown into the chamber byA the rotor every 30 seconds. This resulted in a vigorous agitation of the molten zinc in the chamber which was transmitted to the communicating body of molten zinc in the well. The operating temperature of the condensing chamber was maintained slightly above 500 C. by immersion of a water-cooled shell 22 in the molten metal in the well I2, the immersion area of the shell (of the order of about one-half square foot) being manually regulated in accordance with the temperature of the molten zinc in the well. With continuous overflow of molten zinc from the discharge well I2 into the trough I4, the temperature of the molten zinc in the well is l0-15 C. lower than that of the molten zinc in the condensingv chamber. With manual dipping from the discharge well in the course of which about 1000 pounds of molten Zinc is removed from the well and the depth of molten zinc in the condensing chamber drops from about '7 inches to about 5 inches, the temperature difference between the molten zinc in the chamber and well increases from 10-15" C. at the start of dipping to about 50 C. at the termination of dipping. Dipping takes only a few minutes (usually less than 5 minutes) and may conveniently be carried out at two hour intervals.

The external and communicating body of molten zinc need no t be held in the discharge well of the condenser, but may be an equivalent externally positioned auxiliary cooling well in similar communication with the condensing chamber, as for example at the opposite end or at the side of the condenser. Aside from the fact that molten zinc is not ordinarily removed from such an auxiliary cooling yell, the molten zinc therein is artically cooled and functions in the same manner as herein described with respect to the molten zinc in the discharge well I2. An adequate depth of molten zinc should be maintained in the well I2 or equivalent cooling well to permit such immersion of the artificially cooling means as is required for the practice of the invention. With a water-cooled iron shell I2, a thin coating or crust of solidified Zinc forms on the submerged area of the shell, but this does not adversely affect the cooling efficiency, and moreover protects the iron shell from corrosion by the molten zinc. While it is now our preferred practice to use a cooling shell for the dissipation of heat from the molten zinc in the cooling well, any

other appropriate cooling means may be employed. Whenever situated, the area of communication between the condensing chamber and cooling well should be substantial, and preferably as large as practical, While effectively sealing the condensing chamber against the entrance of atmospheric air, in order to provide an adequate area of heat exchange between the communicating bodies of molten zinc and to provide some agitation or circulation of the molten metal in the cooling well in consequence of the agitation v of the communicating body of molten zinc in the condensing chamber.

We claim:

1. The method of condensing zinc vapor which comprises passing a gaseous stream containing zinc vapor through a condensing chamber having a body of molten zinc therein, maintaining exterorly of the condensing chamber a body of molten zinc communicating with the body of molten zinc in the chamber, effecting intimate i contact between the gaseous stream and the molten zinc within the condensing chamber by hurling molten zinc from said body thereof upwardly into the upper portion of the condensing chamber through which the gaseous stream passes while facilitating circulation of molten zinc between the bodies thereof by the agitation of the body of molten zinc in the condensing chamber, and controlling the operating temperature of the condensing chamber by subjecting said exterior and communicating body of molten zinc to the cooling effect of a stream of extraneous cooling medium flowing through a confined path in said molten zinc but out of direct contact therewith.

2. The method of condensing zincvapor which comprises passing a gaseous stream containing zine vapor through a condensing chamber having a body of molten zinc in the bottom thereof', withdrawing molten zinc from said body thereof into a communicating body of molten zince exterior of the chamber to maintain a practically constant volume of `molten zinc in the chamber, effecting intimate contact between the gaseous stream and the molten zinc within the condensing chamber by hurling molten zinc from said body thereof upwardly into the upper portion of the condensing y chamber through which the gaseous stream passes while facilitating circulation of molten zinc between the bodiesthereof by the agitation of the body of molten'zinc in the condensing chamber, and controllingthe operating temperature of said condensing chamber by subjecting the molten zinc in said exterior and communicating body thereof to the cooling eect of a stream of ex- ERWIN c. HANDWERK GEORGE T. MArmER.

" REFERENCES CITED Y The following references areA of record in the lo le of this patent:

UNITED STATES PATENTS Number Date Name Bunce Aug. 16, 1932 Nelson v-- Feb. 11, 1941 Neve Apr. 15, 1941 Gentil Sept. 1, 1942 Crane et al May 9, 1944 FOREIGN PATENTS Country Date Sweden May 24, 1922 OTHER REFERENCES Chemical Age, November 4, 1944, pp. 447 and

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