US2067394A

US2067394A - Method and apparatus for treating molten metal with gas

Info

Publication number: US2067394A
Application number: US703236A
Authority: US
Inventors: Arthur E Hall
Original assignee: US SMELTING REFINING AND MINING CO
Current assignee: US SMELTING REFINING AND MINING CO; United States Smelting Refining and Mining Co
Priority date: 1933-12-20
Filing date: 1933-12-20
Publication date: 1937-01-12
Anticipated expiration: 1954-01-12

Description

Jan. 12, 1937. A. E. HALL 2,067,394

METHOD AND APPARATUS FOR TREATING MOLTEN METAL WITH GAS Filed Dec. 20, 1935 2 Sheets-Sheet 1 A. E. HALL Jan. 12, 1937.

METHOD AND APPARATUS FOR TREATING MOLTEN METAL WITH GAS Filed Dec. 20, 1933 2 Sheets-Sheet 2 .Other features of the invention consist in the tented Jan. l2, 1%3'7 if j:

METHOD APPARATUS FOR TREATING MOLTEN METAL WI GAS Application December 2t), 1933, Serial No. 703,236

. 19 Claims.

The present invention relates to a method and apparatus for treating molten metal with a gas, designed and adapted more particularly for the treatment of molten lead with chlorine gas for the purpose of removing zinc, as, for example, the zinc left in the lead from the desilvering by the Parkes process.

The principal object of the present invention is to provide a method and apparatus whereby impurities may be removed from a molten metal by means of a gaseous reagent in an expeditious, eflicient, and economical manner, as, for example, zinc from desilvered lead by the use of chlorine gas, without loss or escape of free chlorine into the air, or destructive corrosion of the apparatus, or the necessity of a separate reaction chamber or tank where the chlorine may bebrought into association with a relatively ,smallamount of lead separate and apart from the mass or main body of the molten metal to be treated. Another object of the present' invention is to provide for the continuous and automatic collection and discharge from the molten metal of certainof the products of the reaction, such for example, as the liquid zinc chloride when desilvered lead is treated with chlorine, as fast as produced by the reaction.

A further object is to provide for the absorption of heat generated by the reaction and the application of such heat to the liquid or gaseous reagent for the purpose of supplying the heat required for vaporization and expansion.

With these and other objects in view as will be apparent to those skilled in the art, the present invention consists in the method and apparatus wherein the gaseous reagent is discharged into the mass of molten metal while the latter is caused to circulate within its container or receptacle, the gas preferably being discharged into a downwardly flowing stream of metal.

A further feature of theinvention consists in the use of a. mechanical stirrer, such for example as a rotating screw, positioned adjacent the point of discharge of the gas for the purpose of circulating the metal and distributing the gas.

Still another feature consists in the use of acollector submerged beneath the surface of the molten metal, for collecting such products of the reaction as tend to rise toward the surface of the metal, for example, the zinc chloride following the treatment of lead with chlorine, and disthe same in a continuous stream over the edge of the container under the action of the weight of the metal above the collector.

use of a water cooler for absorbing excess heat from the reaction, of a heating coil with suitable connections for causing the heated water or steam to heat the gas supply, and of a gas discharge pipe or nozzle comprising a tube of non- 5 corrosive material, such as glass, enclosed within a protective metal pipe with asbestos or other suitable packing between to protect the glass tube from excessive heat or jar.

Other features of the invention will be pointed 10 out in the following specification.

In the accompanying drawings which illustrate what is now considered to be the preferred form of the apparatus embodying and practicing the enlarged scale of the gas discharge nozzle or 25 pipe.

The apparatus shown in the drawings comprises, briefly an open hemispherical container or kettle for the molten lead, with a discharge nozzle or pipe for discharging. the chlorine gas 3g from a tank into approximately the center of the mass of molten metal. Mounted upon a. girder framework above the kettle is a motordriven stirrer comprising a vertical screw nornially submerged in the molten metal adjacent the point of gas discharge. The girder. framework also carries beneath it a circular or annular collector, normally held submerged in the molten metal. A cooling coil connected with a water supply is alsosubmerged in the molten metal 40 above the collector, and the hot water or steam from the coil is conducted to a heating coil built into the tank car for heating the liquid chlorine.

Referring to Fig. 1, the container or kettle 6 is of the usual type employed for the treatment of molten metal, being hemispherical in shape and made of steel, with a supporting lip or beading 8 at its edge. Normally resting upon the rim of the kettle, but adapted to be raised and re- 50 moved therefrom, as by a lifting crane, is a framework made up of a lower pair of horizontal girders l0, an upper series of cross-girders l2 secured tothe lower pair at right angles, and diagonal members It attached at their lower inner ends to a plate I6 having an opening I81 to receive the hook of a lifting crane.

Mounted upon this framework is the stirrer or circulating unit comprising a screw 22 on the lower end of the vertical shaft 24, driven by direct connected motor 26 mounted upon two short girder sections 28.

With these parts in operating position, as shown in Fig. 1, the screw or stirrer is positioned approximately at the center of the mass of molten metal, and when driven by its motor creates and maintains a continuous circulation of the metal, with a downwardly flowing stream in the middle of the 'kettle and upwardly flowing streams at the sides.

Preferably a guiding sleeve 30, slightly tapering and open at both ends, is positioned around the screw, extending slightly above the top thereof andterminating a short distance above its bottom, for directing and. controlling more definitely the circulation of the metal within the kettle, as is common in this general type of stirrer or circulating device.

Chlorine gas is delivered directly into the mass of molten metal through the discharge pipe or nozzle 34, from a suitable source of supply, such, for example, as the tank car 36, through the connecting pipe 38. The nozzle 34 is positioned close to the top of the stirrer or screw 22 to discharge its gas downwardly into the downwardly descending and more or less turbulent stream of molten lead, and so close to the screw itself as to cause the latter to effect an intimate association of the gas and lead whereby a rapid and complete reaction between the zinc and gas is assured.

The discharge nozzle or pipe 34 is preferably formed as shown in the enlarged detail in Fig. 4, with an inner tube 40 of pyrex glass surrounded by a wrought iron tube 42 with end cap 44. A packing 46 of asbestos or other suitable heat resisting material, is inserted between the pyrex glass tube and the protective metal tube to protect the pyrex from the heat of the lead and to cushion it from jars or vibration. A section of rubber hose or tubing 48 provides a yielding co nection between the discharge nozzle and the metal pipe 38 leading from the source of supply.

As the gas reacts with the molten metal, and more particularly with the zinc contained therein to form zinc chloride, the latter product, being of less specific gravity than the molten metal, rises, but before it can reach the surface of the molten mass is intercepted bythe collector indicated generally at 50. This comprises a circular annular top 52 having depending inner and outer' marginal walls 54 and 56. The collector is supported a short distance below the surface of the molten metal, as shown in Figs. 1 and 2, by means of long bolts 58 extending from the cross girders 12 into the top of the collector adjacent its outer margin. An outlet or discharge duct is provided for the collector consisting of an upwardly extending passage 60 at one side thereof, with a slightly descending spout 62 projecting beyond the rim of the kettle to discharge the molten zinc chloride in a continuous stream into the receptacle or kettle 64.

In order to facilitate the collection and discharge of the zinc chloride, thetwo halves of the annular top of the collector are slightly inclined upwardly towards each other, as shown in Fig. 1, while at the same time the collector as a whole is inclined upwardly toward the discharge, as

shown in Fig. 2. Thus the liquid zinc chloride, as it rises through the molten mass of metal, is intercepted by the collector and directed toward the discharge, all under the influence of the weight of the molten metal lying above the collector. This automatic collection and discharge of the zinc chloride will continue so long as chlorine is discharged into the mass of lead and there remains any appreciable amount of zinc with which it may react.

Due to the agitation of the molten metal, there is a tendency for the level of the zinc chloride to rise and fall at the discharge, and in order to avoid or limit such variations in level, a baflie plate 66 has been positioned immediately beneath the discharge passage 60.

The reaction of the chlorine with the zinc in the molten metal generates heat in excess of that required to maintain the metal in proper molten condition, and in order to abstract and withdraw such excess heat a cooling coil has been provided which is connected with a water supply. Preferably this cooling unit is mounted on the top of the collector and in close proximity thereto so that it may have a cooling effect upon the zinc chloride as well as upon the molten metal. As shown in the drawings the cooling coil 68 is submerged in the molten lead and positioned close to the top of the collector, being connected with the water supply by the water pipe 10. The hot water or steam generated by the heat of the molten material will be discharged through the pipe 14, either to waste through the connection 18, or through a heating coil to heat the supply of chlorine. Preferably the chlorine supply will be in the form of liquid chlorine delivered from a tank car 36, as shown in Fig. 1. These cars are constructed with inner and outer shells 82 and 84 respectively, with a filling of heat insulating material between. At the. bottom of the tank car between the shells and imbedded in the insulating material .is a. series of heating pipes 88 with inlet and

outlet connections

90 and 92. By means of the connection 94 the hot water or steam from the cooling coil 68 will be passed through the heating coil of the tank car and discharged to waste at 96, the heat of reaction thus supplying the heat necessary to vaporize and heat the chlorine.

If sufficient heat is not available from the reaction properly to heat the chlorine, as, for example, in the winter months when atmospheric temperatures are low, a source of live steam supply may be provided as at 98, which, through suitable valved connections, may be passed through the heating coil in the tank car while the heated water or steam from the cooling coil in the kettle is discharged to waste at 18.

Preferably the water cooling coil 68 is connected to the Water supply and discharge piping with rubber hose, as shown at I00, so that the coil may be disconnected from the water supply in order to permit the coil to be raised with the collector and the other parts when the framework is lifted from the kettle.-

Similarly, provision is made for disconnecting the gas dischargepipe by means of the rubber hose I04. In practicing the process by the use of the above described apparatus, the kettle will be filled with the molten metal to be treated, as for example, following the Parkes process where silver has been removed by the use of zinc, leaving the zinc in the lead.

If the superposed mechanism has been removed for the p rp e of facilitating charging of the kettle, the mechanism will be replaced by the crane, with the screw, collector and coil submerged in the molten metal. The gas discharge pipe is next inserted, being passed downwardly through the annular opening in the collector and secured in position with its discharge end adjacent the top of the screw. The motor isv now set in operation to start the circulation of the molten lead, and as soon as this is accomplished, the flow of chlorine gas from the tank car or, other source of supply is started. The amounts to be admitted must be no more than can react with, and be absorbed by, the molten metal. If free chlorine appears at the surface of the molten metal, it is evident that the gas is being supplied at too fast a rate and must be cut down.

By reason of the circulation set up in the mass of molten metal and the downward discharge of the gas into the downwardly moving stream of metal at a point adjacent the rapidly rotating screw, the reaction between the gas and zinc is relatively rapid and the chlorine may be fed into the mass of molten metal at a relatively high rate. For example, with a kettle approximately fourteen feet in diameter, containing two hundred and thirty-five tons of molten metal, and with a screw rotating slightly less than twelve hundred R. P; M. and absorb about twenty horse power, the chlorine may be fed at a rate of from live to six pounds of gas per minute without free chlorine appearing on the surface.

As the reaction proceeds and heat is developed, water is passed through the cooling coil at a rate controlled by the water supply valve, and proper to maintain a constant temperature of about 670 F.

The heated water or steam coming from the coil may be conducted to the hea'tingcoil in the tank, or if by reason of weather conditions or otherwise this does not supply sufiicient heat for vaporization, the cooled water may be discharged to waste and live steam from some suitable source passed through the heating coil in the car to vaporize the liquid chlorine.

The chlorine reacts with the zinc to form zinc chloride according .to the general formula This gives zinc chloride in liquid form which, because of its specific gravity relatively to the molten metal, rises through the latter until it is intercepted by the collector. The inclination of the top of thecollector and the pressure of the metal above the collector causes the zinc chloride to fiow to the discharge where it rises and flows over the rim of the kettle into the adjacent collecting kettle.

So long as chlorine continues to be supplied, and there remains any substantial amount of zinc, the reaction will continue and liquid zinc chloride will be constantly and automatically col-= lected and discharged. The completion of the reaction will be indicated by the change in the In the commercial use of the present invention, the zinc content in the treated lead will be reduced to .005%. An even lower content could be secured if desirable or necessary by continuing the process under carefully controlled conditions, but inasmuch as further treatment of the lead is required for the removal of other impurities, which treatment also removes the remaining small amounts of zinc, it is ordinarily not commercially profitable to carry the process beyond that required for the .005% zinc content.

Corrosion is reduced to a minimum through the delivery of chlorine gas into the mass of molten metal, so that the reaction take place and the chlorine is absorbed in the zinc while it is still surrounded by a protective mass of lead. The location of the gas delivery nozzle, preferably slightly to one side of the stirrer or screw as shown in the drawings, insures continuous contact of the screw with only the molten metal, thus protecting it from direct contact with, and corrosion by, the chlorine gas.

The maintenance of circulation of the molten metal in distinct downwardly and upwardly flowing currents not only facilitates the reaction by bringing the gas into more intimate mixture with the metal, but by reason of the discharge of the gas in the downwardly flowing stream, tends to prolong the time appreciably for the reaction and reduces the tendency of free chlorine to rise to the surface. The upwardly flowing currents also expedite the rising movement of the zinc chloride and its collection by, and discharge from, the collector.

While the present process and apparatus have been described in connection with the treatment of lead with chlorine gasfor the purpose of removing zinc, it is to be understood that the invention is not limited to such materials or use but may be employed with other materials or metals or gas having the proper reactions with respect to one another. 7

Having thus described the invention, what is claimed is:

1. The method of treating molten metal with a gas which consists in causing the metalto circulate in downwardly and upwardly flowing streams, discharging the gas into the downwardly flowing stream, and segregating from the upwardly flowing stream and beneath the surface of the molten metal the products of the reaction. 4

2. The method of treating molten metal with a gas which comprises segregating beneath the surface of the metal the products of the reaction which tend to rise to the surface of the metal, discharging such products from beneath the surface of the metal, and abstracting heat from the molten metal adjacent the point of segregation.

3. Apparatus for treating molten metal with gas comprising a container for holding a mass of molten metal, means for bringing gas from a source of supply into contact with the molten metal, and, a submerged collector beneath the surface of the molten metal to collect the products of reaction which tend to rise to the surface of the metal.

4. Apparatus for treating molten metal with gas comprising a container for holding the molten metal, means for bringing gas from a source of supply into contact with molten metal, and a submerged collector beneath the surface of the molten metal to collect the products of reaction which tend to rise to the surface of the metal.

the collector having discharging means for conducting the collected products upwardly and laterally over the edge of the container under the action of the weight of the molten metal overlying the collector. 7

5. Apparatus for treating molten metal with gas comprising a containerfor the molten metal, means for bringing gas from a source of supply into contact with the molten metal and a submerged collector beneath the surface of the molten metal to collect the products of reaction which tend to rise to the surface, the collector having a duct for conducting the collected products upwardly and laterally, and.a baflie :adjacent the inner opening of the discharge duct.

6. Apparatus for treating molten metal with gas comprising a container for holding the molten metal, a source of supply of liquefied gas, means for bringing the gas into contact with the molten metal, and means for transferring heat from the molten metal adjacent the collected products to the liquefied gas supply.

7. Apparatus for treating molten metal with gas comprising a container for holding the molten metal, a source of liquefiedgas supply, means for bringing the gas into contact with the molten metal, a cooling coil in the molten metal for absorbing heat therefrom, a heating coil for heating the liquefied gas, and connections between the cooling and heating coils whereby heat may be absorbed from the molten metal and delivered to the liquefied gas.

8. Apparatus for treating molten metal wit gas comprising a container for holding the molten metal, a gas pipe for bringing gas from the source of supply into contact with the molten metal, power-driven means for causing the metal to circulate inthe container, a collector for collecting the products of reaction which tend to rise to the surface of the metal, and a support, separable and removable from the container, for commonly supporting said powerdriven means and the collector with the collector normally held submerged beneath the surface of the molten metal.

9. Apparatus for treating molten metal with gas comprising a container for holding a mass of molten metal, the container being'circula'r in cross-section, an annular collector having a central opening and with its marginal edge spaced inwardly from the container, a vertical shaft extending downwardly through a central opening in the collector, a screw mounted thereon for causing circulation ofthe metal, means for driving the shaft and screw, and a gas pipe extending downwardly through the axial opening of the collector for delivering gas from the source of supply into the molten metal.

10. The method of using a liquefied gas for the treatment of molten metal which consists in abstracting heat from the molten metal; applying such abstracted heat to the liquefied gas to vaporize the same, and thereafter bringing the gas into contact with the metal.

11. That step in the method of treating molten metal with a reagent which consists in segregating beneath the surface of the metal the products of reaction which tend to rise to the surface. I

12. That step in the method of treating molten metal with a reagent which consists in segregating beneath the surface of the metal, the products of reaction which tend to rise to the surface, and in continuously withdrawing such segregated products. 4

13. The method of treating molten metal with a reagent which consists in intimately associating the metal and reagent to cause reaction there between and thereby to form a mixture of the metal and the products of suclr'reaction and segregating beneath the surface of the metal the products which tend to rise to the surface.

14. That step in the method of treating molten metal with a gas which consists in segregating beneath the surface of the metal the products of the reaction which tend to rise to the surface of the metal, and by meansof the weight of the metal above the segregated products discharging said products above the level of the surface of the metal.

15. Apparatus for treating molten metal with gas comprising a container for holding a mass of molten metal, means for causing the molten metal to circulate within the container, a gas pipe for delivering the gas from a source of supply into the metal, and means for segregating 'beneath the surface of the metal the products of reaction and for continuously discharging from beneath said surface the segregated products.

16. Apparatus for treating molten metal with gas comprising a container for holding a mass of molten metal, the container being of substantially hemispherical shape, means for imparting a downward fiow to the gnetal adjacent the vertical axis of the container and an upward fiow adjacent the container wall, a gas pipe for discharging gas from a source of supply into the downwardly flowing stream of metal, and an annular collector for collecting the products of the reaction which tend to rise to the surface of the metal adjacent the container wall.

17. Apparatus for treating molten metal with gas comprising a container for holding the molten metal,.means for bringing 'gasfrom a source of supply into contact with the molten metal, a collector submerged in the molten metal and exposed to the heat thereof for collecting the products of reaction, and a cooling coil submerged in the molten metal adjacent the collector for continuously absorbing heat therefrom to prevent overheating of the products of reaction.

18. The method of treating molten metal with a reagent which consists in intimately associating the metal and reagent to cause reaction therebetween to form a molten mixture of the metal and the product of such reaction, segregating the products of reaction in molten form beneath the surface of the metal, and discharging the segregated product while still in molten form from beneath the surface of the metal and at a level above the surface of the metal.

19. The method of treating molten lead with chlorine gas to'remove zinc which consists in introducing chlorine ,into the molten lead to form zinc chloride, collecting the chloride in liquid form beneath the surface of the molten lead and discharging the liquid chloride from beneath the surface of the lead.