US2766034A - Condensation of metallic vapors - Google Patents

Description

Oct. 9, 1956 H. K. NAJARIAN 2,766,034 CONDENSATION OF METALLIC VAPORS Filed March 13, 15552 4 Sheets-Sheet 1 INVENTOR HERAND K. NAJARIAN ATTORNEYS Oct 9, 1956 H. K. NAJARIAN 2,766,034

CONDENSATION OF METALLIC VAPORS Filed March 13, 1952 4 Sheets-Sheet 2 INVENTOR HERAND K. NAJARIAN ATTORNEYS Oct. 9, 1956 H. K, NAJARIAN CONDENSATION OF METALLIC VAPORS Filed March 13, 1952 4 Sheets-Sheet 3 INVENTOR HERAND K. NAJARIAN ATTORNEYS Oct. 9, 1956 H. K. NAJARIAN CONDENSATION OF METALLIC VAPORS 4 Sheets-Sheet 4 Filed March 15 195i INVENTOR HERAND K. NAJARIAN ATTORNEYS 2,766,034 CONDENSATION F METALLIC VAPORS Herand K. Najarian, Beaver, Pa., assignor to St. .loseph Lead Company, New York, N. Y., a corporation of New York Application March 13, 1952, Serial No.

7 Claims. ((11. 266-37) In the above-mentioned U. S. and

is continuously maintained at a minimum or preselected level consistent with practical, operation.

Another object of the invention is to provide a method and apparatus for condensing metallic vapors wherein is eliminated the destructive efi'ects of thermal shock to the condenser shell which result when cooling water is meant Patented Get. 9, 1956 applied over the hot shell after shutdowns for clean-outs, repairs, power failures, etc. In accordance with the present invention, no cooling water need be applied to the condenser shell.

Another object of the invention is to and apparatus for condensing metallic side of the bafiie means.

the receptacle,

In its method aspect, the invention comprises condensing vapors of metals from a stream of gas carrying the gas upwardly through a body of between a lower path to the lower portion of the restricted path by utilizing the head created by the upward transportation of metal.

The apparatus of the invention preferably includes an inclined, refractory lined metal tube with upwardly projecting, vertically disposed, insulated connecting conduits at each end, whereby a mass of molten metal is maintained in the inclined tube portion thereof. Suction is applied to the above assembly through the vertical conduit contiguous to the higher end of the inclined tubular condenser portion. Hot gases, for example from a reduction furnace, comprising metallic vapors and accompanying gases from which air is excluded, are admitted to the condenser through the insulated vertically disposed conduit contiguous to the lower end of the inclined tubular condenser portion.

The suction, applied above the level of molten metal at the gas discharge end, is of such magnitude as to raise and maintain the level of the upper exposed surface of the molten metal in the inclined tube at a substantial height above the lower exposed surface of molten metal and to depress and maintain the lower surface at a level that permits the vapor and gases to enter the. mass of molten metal at a lower exposed surface.

The metallic vapor and gases are mai. tained submerged in said mass of molten metal by the roof portion of the inclined tubular condenser and travel upwardly and forwardly in an inclined path through a circumferentially confined mass of molten metal, inducing a how of molten metal concurrent to the vapors and gases bubbling through the mass of molten metal. The metallic vapors are condensed to coherent liquid metal by contact with the molten metal and internal surfaces of the condenser wiper by the metal, while the uncondensed vapor and gases escape, after passing through the mass of molten metal, into the connecting outlet conduit, and thence through suitable conduits to a suction-producing device such as a vacuum pump.

The heat energy released by the condensation of the vapors of volatile metals into liquid raises the temperature of the mass of relatively cool molten metal held in the condenser. To secure continuous efficient condensation of metallic vapors, it is necessary to extract the heat energy from the mass of molten metal in the condenser and maintain the temperature thereof as low as and as near the melting point of the metal as practical operational procedures permit, for reasons more fully explained hereinafter. Heretofore cooling of the mass of molten metal in the condenser has usually been accomplished by applying cooling medium such as water to the outside surface of the refractory lined steel shell of the condenser. However, the low rate of heat transfer through the inside refractory lining of the condenser and the relatively limited path of circulation induced within the condenser by bubbling vapors and gases impose definite rate of cooling of the mass of molten metal in the condenser, making it diflicult to maintain a uniform optimum temperature level necessary for efiicient condensation of vapors and resulting in excessive blue powder formation and low condensation efficiency.

In accordance with the preferred method of this invention, continuous and efficient cooling of the mass of molten metal is obtained by continuously diverting a portion of the molten metal from the condenser to an outside cooling receptacle through a conduit connected to the condenser near the gas outlet end, cooling the portion ofmolten metal while it flows through the outside receptacle, and returning at least a portion of the diverted and cooled molten metal back to the condenser through a second conduit connecting the outside receptacle to the condenser near gas inlet end thereof. The outside receptacle, hereinafter called the tapping well, is, in the simplest form, a refractory lined and insulated vessel preferably openon The diverted increment of molten metal flows out from the condenser to the outside tapping well, through limitations on the.

the tapping well, and back to the condenser entirely by gravity-circulation and preferably without the aid of power driven impellers, pumps, and the like. The gravity flow of molten metal is induced by hydraulic head created within the mass of molten metal in the condenser by air-lift action of metallic vapors and gases bubbling in an inclined path upwardly through the molten metal near the roof portion of the condenser, forcing some of the molten metal upwardly towards the gas discharge end of the mass of molten metal, while the return of an equivalent amount of metal through the bottom portion of the condenser back towards the lower end of condenser is prevented or substantially prevented by baffles positioned crosswise of the condenser and acting as dams. Thus, the level of molten metal at the gas outlet end of the condenser. is raised higher than the level otherwise attained solely by suction applied thereon. This added height of metal forces a portion of the molten metal out through the upper conduit into the tapping well and, in turn through the second conduit near the lower end of the condenser, back into the condenser. This flow continues as long as suflicient suction is applied at the upper end of the inclined condenser tube to draw vapors and gases through the molten meta As the portion of molten metal flows through the tapping well, it is cooled by suitable means, as for instance by natural direct radiation from the mass of metal inthe tapping well, by cool air circulation around the tapping well, or, in addition, by having the molten metal come in contact with cooling surfaces such as a pipe coil carrying water and immersed in the flowing metal. The rate of cooling is regulated as for example by varying the extent of immersion of the cooling coils in the flowing molten metal, and in turn dictated by the desired temperature level in the mass of molten metal in the condenser for continuous practical and efficient operation. For example, in zinc condensers of the type of the present invention, attached to large electrothermic furnaces and employing the cooling method described herein, it is possible to maintain the temperature of the molten metal in the condenser at from 475 C. to 525 C. continuously, in which temperature range a very small amount of blue powder is formed and condenser eliiciency is very high. The importance of efficient cooling of moltenmetal in the condenser and maintenance of temperature at the lowest level possible in practical operation will be seen from the following table from which it is apparent that blue powder formation, which is a direct functionof theoretical uncondensable zinc, increasessharply as the temperature of the condenser increases, being very low at temperatures near the melting point of zinc, for exam-. ple, only one-half of one percent at 500- C.

TABLE I Uncondensed-zincvapor, at equilibrium conditions Theoretical Minimum Un- Condenser Vapor Presecndensublc Temperature, sure of Zinc, Zinc as Pereg. G. Min. Hg centage of Slab Zinc Produced a 4.50 0. 4a 0. 2 500 1. 30' 0. 5 550 37 1.5 560 4. s0 1. a 570 0. 00 I 2. 3 cs0 7. 40 2. s 590 0. 00 3. 5 600 n. 00 t 4 010 1a. 20 r 620 is. 00 0. 5 630 10. 00 l s. 0 040. 22. 50 0.7 650 as. 70 it. 0 I 6000 3c. 3

A1: 16 m. Hg vacuum (29.2 in. 11g barometer) and 45 percent Zn vapor,

55 percent noncondensable gas mixture entering condenser.

'metal 2 and having a vertically duit 3 communicating with the the entire condenser assembly.

Improvement in condensing efliciency, realized by the present invention increases the over-all capacity of the condenser assembly in terms of tone of zinc produced the condenser, and longer periods between shutdowns for rehabilitation.

The invention will be described with greater particularity with reference to the drawings in which Fig. 1 is a vertical longitudinal sectional view of one form of zinc condenser embodying the invention;

Fig. 2 is a plan view thereof;

Figs. 3, 4 and are transverse sectional views taken along the lines 33, 44 and 55, respectively of Fig. 1;

Fig. 6 is a plan view of another form of cooling chamber or tapping well;

Fig. 7 is a sectional view taken along the line 7-7 of Fig. 6; and

Fig. 8 is a sectional view taken along the line 8-8 of Fig. 6.

Referring to the drawings, particularly to Figs. 1 to 5 thereof, the condensing apparatus shown is especially adapted for condensing zinc vapors, either pure or impure, from zinc reduction furnace gases. The condensing appa- -ratus has a tubular condensing receptacle 1, inclined from 10 to 45 to the horizontal, preferably inclined 12 to 18 degrees from the horizontal, holding a mass of molten disposed gas inlet conlower end. of the condensing receptacle and a connection 4 and thence through pipe 6 to the vacuum pump, not shown. The air-lift action produced by the gases bubbling through the portion of the body carries forward and gases towards the upper the mass of molten metal.

A batfie 9 is positioned transversely within the condenser 1 at a point approximately mid-way between the ends of the tube. The bafile together with the tube provides a large opening 10 adjacent the roof of the tube and a very much smaller opening 11 adjacent the floor of the tube. A second parallel baflie 12 is positioned in and an opening 14 adjacent the floor that is considerably larger than the opening 11. By virtue of the air-lift bubbling up through the extreme case, the opening 11 may be dispensed with entirely, the battle 9 extending to the floor of the tube. For practical reasons a small opening 11 is desired.

Weaton et al. patent, it has been found desirable to use one or more bafiies or dams to prevent high amplitude surging of the large mass of molten metal. That is, the dams served as damping devices. In effect, the present invention utilizes the damping energy to cause the above described fiow of metal.

All parts of the apparatus contacted by liquid metal are refractory lined, suitably by pre-fired shapes of silicon carbide. The open outside receptacle 17 serves well and as a heat transfer region.

tapping well. The small portion of blue powder which molten metal cirthe surface of the may nevertheless be entrained in the culating through the vessel 17 comes to metal in the tapping well 17 and is skimmed from time to time. If molten metal in the condenser intermediate the baffie 9 and the upper exposed surface of the metal is prevented from flowing downwardly, as for instance by closing or greatly constricting orifice 11 at the bottom of baffie 9, the molten metal being carried upwardly towards the upper exposed surface of the metal flows at a greater rate through conduit 16 to the outside receptacle 1'7 and thence back into the condenser through the conduit 18. Preferred practice is to make orifice 11 at the bottom of bathe-9 small enough, usually 1 /2 to 2" in diameter, to permit complete draining of molten metal from the condenser throughan orifice at the lowest place in the condenser, as for instance at tap hole. 15, yet offer sufficient constriction to permit substantial flow of molten metal out of the condenser to the outside tapping well.

In the preferred method of cooling the metal in the tapping well, the cooling coil 19, the lower part of which is immersed in molten metal flowing through the tapping well 17, is moved up and down by a hoist, not shown, to vary the extent of cooling surfaces immersed in the molten metal, thus controlling the temperature of the flowing molten metal and, in turn, the temperature of the mass of molten metal held in the condenser.

Liquid metal, as condensed from vapors during operation, preferably is allowed to accumulate in the condenser. Periodically, tap hole 20 on the cooling receptacle 17 is opened and a portion of liquid metal is tapped out and cast into slabs. The condenser may be emptied out completely, as for instance at the end of a campaign, through bottom tap hole 15 which is normally closed during the entire campaign.

Vacuum type condensers of large capacity having the preferred cooling apparatus, including an external tapping well with cooling coils and attached to the condensing unit, substantially as described herein, may be operated for long periods condensing upwards of 40 tons of zinc metal per day from zinc vapor and gases produced in large electrothermic zinc furnaces. Condenser temperatures in the neighborhood of 500 C. are easily maintained, at which temperatures very eificient condensation of zinc vapors from furnace gases is realized.

As an example, a condenser assembly having a tapping well with a cooling coil made of 2-inch pipe carrying cold water at 65 5. receives zinc vapors and CO gas mixture from an electrothermic zinc furnace. The condenser holds a normal charge of approximately 40 tons of molten metal and condenses zinc vapors to metallic zinc at an average daily rate of 20 tons. Temperature of the metal in the condenser is maintained at 500 C. to 525 C.

Zinc metal flows out of the condenser to the tapping well and back into the condenser at the rate of approximately 120 tons per hour. The temperature of the metal flowing through the tapping well and around the cooling coils drops an average 10 C. to 12 C.

Figures 6, 7 and 8 show in plan and sectional views a modification of the outside cooling receptacle whereby, when there is an appreciable amount of metallic lead found in the condensed zinc, the major portion of the metallic lead is separated by settling and separately drawing it off from a stand-pipe attached to and communicating with the outside receptacle. When lead ores smelted in a lead blast furnace contain high percentages of zinc, practically all the zinc content of the ore, together with small amounts of lead, find their way into the slag drawn ofi the blast furnace. When such slag is smclted further to extract the metallic constituents, as for example in a slag bath electric furnace, the zinc and lead compounds are volatilized from the slag, and both are reduced to the metallic state as ti ey pass through the bed of overlying reduction fuel and pass out of the furnace into the zinc condenser mainly as metallic vapors. Depending on the lead content of the liquid slag bath in the furnace,

8 the. zinc condensed may carry, metallic lead.

When impure zinc ores or concentrates having appreciable amount of lead are smelted, the gaseous prod! ucts. from the reduction furnace comprising the metallic vapors and accompanying non-condensible gases may carry substantialamounts of reduced volatile compounds of lead entrained with zinc vapors. Depending on the lead content of such impure zinc ores or concentrates, the liquid zinc condensed from such gaseous products may carry appreciable amount of metallic lead, as for example 1 to 5%.

Referring to Figures 6, 7 and 8, a portion of the bottom of the outside cooling receptacle 17 is depressed to form a well 21. A refractory lined stand-pipe 22 is attached to the outside cooling receptacle 17' by arefractory lined conduit 23, thus connecting the cooling receptacle with the stand pipe at or near the bottom of the depressed well portion of the outside cooling receptacle. During operation, metallic lead 24, separating from the molten zinc 25 by gravity, collects at the bottom of the well and communicating stand pipe 22. As metallic lead accumulates at the bottom of the outside cooling receptacle 17, the level of lead in stand pipe 22 rises somewhat, the level of molten lead in the stand pipe being lower than the level of molten zinc flowing through the cooling receptacle 17' to an extent dependent on the difference in specific gravities of metallic Zinc and lead and the height of metallic lead in the cooling receptacle. In order to prevent molten zinc from finding its way into the stand pipe, a sufficient amount of molten lead is poured into the assembly at the start of operations, before the priming charge of molten zinc is filled into the condenser and cooling receptacle. Molten lead is tapped out of the stand pipe at intervals and as molten lead aecumulates-by opening lead tap hole 26.

I claim:

1. Apparatus for condensing metals from a stream of gas carrying the same comprising an inclined tubular member, gas outlet means communicating with the upper end of said tubular member, wall means providing a liquid receptacle communicating with the lower end of said tubular member, gas inlet means communicating with said liquid receptacle above the level of communication of the tubular member therewith, transverse dam means in said tubular member intermediate the ends thereof, the upper edge of said dam means being spaced from the roof of said tubular member to permit upward flow of gases. and liquid metal adjacent the roof of the tubular member while preventing substantial downward flow of liquid metal adjacent the floor of the tubular member, means providing a cooling chamber adjacent said tubular member, first conduit means connecting said cooling chamber with said tubular member at one side of said dam means and second conduit means connecting said cooling chamber with said tubular member at the other side of said dam means.

2. Apparatus as defined in means in said cooling chamber.

3. Apparatus as defined in claim 1 wherein said cooling chamber means has a well, a stand pipe adjacent said cooling chamber means, and conduit means connecting said well to said stand pipe.

4. Apparatus for condensing vapors of metals from a stream of gas carrying the same comprising a heat insulated entrance chamber connected to a source of gases and said vapors, an exit chamber, a receptacle having its respective ends connected to said chambers and normally tfilled with molten metal for a substantial portion of its length, a suction producing device to draw ofi gases from said exit chamber and to lift the exposed upper surface of said metal substantially above its exposed lower surface, an enclosing r-oof portion to said receptacle in contact with and confining said molten metal intermediate said chambers, dam means submerged in the liquid for example 1 to 5% claim 1 including cooling metal in said receptacle the upper edge of said dam means being spaced from the roof of said receptacle to permit upward flow of gases and liquid metal adjacent the roof of the tubular member and any opening in the lower part of said dam means being much smaller than the space between the upper edge of the dam means and the roof of said receptacle to prevent substantial downward flow of liquid metal adjacent the floor portion of said receptacle from the exit chamber side of said dam means to the entrance chamber side of said dam means, means providing a cooling chamber external to and [adjacent said receptacle, first conduit means connecting said receptacle at a point submerged in said metal on the exit chamber side of said dam means to said cooling chamber, and second conduit means connecting said cooling chamber to said receptacle at a point submerged in said metal on the entrance chamber side of said dam means.

5. Apparatus as defined in claim 4 including a cooling coil in said chamber and means for varying the area of cooling coil exposed to liquid metal in said cooling chamber.

closing roof portion is inclined 6. Apparatus as defined in claim 4 wherein said enat an angle of from 10 to 45 from the horizontal.

7. Apparatus as defined in claim 4 wherein said enclosing roof portion is inclined at an angle of from 12 to 18 from the horizontal.

References Cited in the file of this patent UNITED STATES PATENTS

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