US2458253A - Apparatus for metals distillation - Google Patents

Description

Jan. 4, 1949. n. s. cHlsHoLM Er- AL 2,458,253

APPARATUS FOR METALS DISTILLATION Filed nay so, 1945 2 sheets-sheet 1 Coo/ing lAir ATTORNEYS Patented Jan. 4, 1949v Ni'r ' STATES PATENT.

ori-ICE APPARATUS Fon METALS DIsTrLLA'rIo'iv Douglas S. Chisholm and Thomas Griswold, Jr., Midland, Mich., assignors to The Dow Chemical Mich., a lcorporation of Company, Midland, Delaware This invention relates to apparatus for the distillation of metals. It particularly concerns improved means for disposing the feed meta1 in the vaporizing zone in the form of a continuously owing thin film.A

' A number of metallurgical processes involve` distilling a desired metal from an alloy thereof Application May 30, 1945, Serial No. 59,710

2 claims. (chess- 19) rates can be realized without overheating` the feed to the point that boiling and its resulting entrain- Y ment of alloy in the vapor occur. Another object is to provide a still in which no part of the feed Ialloy can become stagnant, and in which molten metals containing solid matter in suspension can with less Volatile metals. In certain .of these when the alloy is heated drastically. In such a be handled without dilculty.

In metallurgical stills according to the invention, the feed alloy is introduced into a shallow spiral trough which slopes continuously down the vaporizing section of the still. During its traverse of the trough, the alloy is heated toa distilling case, the action is usually so violent that there is a serious entrainment of the boiling alloy in the evolving vapors, with a corresponding decrease in the purityof the distilled product. In designing a still for Vaporizlng metals, then, one of the ma- `ior problems is to provide means for disposing the feed alloy in a form such that it will Apresent a maximum surface area for the disengagement of vapor and yet will not be subject to such overheating as produces violent boiling.

One solution to `the problem'is to arrange in the vaporizing section of the still a number of superposed trays which hold the metal as a series;

of pools through which it flows While it is being heated. Unfortunately, since in this design structural limitations usually require that the trays be 'of substantial depth, stagnation of apart of the metalA invariably occurs. In addition, since the ratio of vapor-disengaging surface of the metal to total metal volume is small in the case of deep trays, adequate vaporizing rates can only be obl tained either by going to a still which has a contion to provide an improved metallurgical stillin which the ratio of vapor-disengaging area to metal volume is large, sothat high vaporlz'ing temperature and evolves vaporsof the volatiliza.- ble component rapidly and effectively without undergoing ebullition,l Because of the slope of the trough, the' alloy is in continuousv now at all times while it is being heated. lis a result,4all portions ofthe heated metal are repeatedly brought to the vapor-disengaging surface of the flowing stream to release their volatilizable component; stagnation does not occur. In addition, solid particles entering with the feed are washed through to the outlet by the moving metal; the still is thus to a large extent self-cleaning.

The invention may be further explained'with reference to the accompanying drawings, in which:

Fig. 1 is a vertical assembly, largely in crosssection, of one form of metallurgicalistiil embodying the invention;

Fig. 2 is a vertical cross-section of a portion of the vaporizing zoneof a still embodying another form of the invention; and

Fig. 3 is a fragmentary perspective view of the construction shown in Fig. 2. a

The apparatus may be described with reference to the distillation of magnesium from a leadmagnesium alloy in which lead preponderates, although it is to be understood that the invention is not thus limited.

In the equipment of Fig. 1, the liquid lead-magnesium alloy to be distilled is stored in an alloy steel tank 4 surrounded byinsulating brick i.

-The alloy is withdrawn by a sump pump 6 driven by' a variable-speed motorr 1 and is forced through a feed line 8A into the top of the vaporizing section of the still 9. Y

This still is constructed of a large-diameter alloy steel pipe set vertically and provided at the lower end with a conical bottom l0 from which a drain pipe Il extends into the reservoir 4. At

. the upper end, the still is closed' by, a anged dome l2 from which a vacuum line I3 leads to an exhaust pump I4, the. line being provided with a clean-out flange i5. The still is divided into a formed, for convenience, of three pieces held together by dowels 23. The pillar rests on a graphite plate 24, which ts snugly into vthe bottom piece IU and is provided at its edge with one or more drain holes 25, and is secured at the top by alloy steel hold-down lugs 26 welded tothe wan of the stm. A cup 2l is formed in the top of the pillar v22 to receive alloy issuing from the feed pipe 9.

In the side of the pillar 22, there is cut a spiral alloy-carrying trough 28, starting' at the cup 21 and continuing at a smooth slope until it runs out at the bottom just above the support plate 24. The precise cross-sectional shape of the i trough is not critical, but it is highly desirable that its rdepth be a minor fraction of its width, i. e. that the trough be as shallow as possible. It is likewise preferable that the downward slope of the trough be gentle, which is achieved by cutting thespiral with a pitch which is a minor fraction of the diameter vof the pillar 22, as shown in Fig. 1. The base diameter of the pillar should ordinarily be nearly equal to the inside diameter of the still, while thetop diameter is preferably a major fraction of the still diameter.

Magnesium vapors generated in the Vaporizing section I6 escape upwardly into the condensing section I'l, where they come into con-4 tact with the cooled walls and are condensed to liquid magnesium. The condensateA trickles down into an vannular collecting gutter 29 welded to the wall of the condenser at the bottom, and from there'runs through a product line 30 into a holding-pot 3l set in brickwork 32 and fired by a gas burner 33.

The alloy tank 4 and condenser ll are provided wth heaters as shown, and the associated pipes 8, Il and 30 with heaters, not illustrated, to raise them to the appropriate temperatures when beginning operation. These parts are also jacket-ed with thermal insulation, not shown, to prevent freezing of the lead-magnesium alloy and the magnesium product once circulation is established.

In operation of the apparatus shown in Fig. 1, the lead-magnesium alloy in the tank 4 is kept under a protective saline flux or inert gas atmosphere. The tank'4 and feed line 8 are maintained at a temperature above the freezing point of the alloy, preferably at 550 to 600 C. The burners 28 are adjusted to maintain the lower section I6 of the still at a vaporizing tempera- Y ture, usually 775 to 875 C., and the cooling air to the condenser I1 is controlled so that the temperature 'of the magnesium condensate is above its freezing point (651 C.), preferably 655 to 665 C. The lexhaust pump I4 is operated to hold the still at a pressure which is suiciently reduced to permit boiling to take'place at a high rate, but is above the vapor pressure of the magnesium condensate; absolute pressures between 0.i and about 0.5 inch of mercury are most satisfactory. At this pressure, the alloy in the feed line 8 and the return drain II, and the magnesium in' the product line-30 rise to levels well abovel those of the tank 4 and pot 3l, forming barometric seals.

The motor l is adjusted so that the pump 6 forces lead-magnesium alloyat a desired ratev into the still, where it falls into the Icup 21. The alloy then flows continuously down the convolutions of the spiral trough 28 and finally through the openings 25 and out the drain Il, being' at the same time heated by radiation from the hot wall I6 and by contact with the pillar 22 which is lself heated by radiation. As the alloypasses ldown the trough 28, part of the magnesium in it is vaporized without appreciable occurrence of ebullition and with little,

if any, entrainment of the alloy. The vapors rise it may be cylindrical, in which case its diameter would have to be considerably less than that of the still.

The use of graphite or other carbon asa material of construction for the pillar 22 is preferred because of its inertness to thermal shock,

its high emissivity, which is importantv where the pillar is to be heated by radiation, and the fact that it does not corrode with introduction of undesired substances into the iowing alloy. However, the pillar may, in some instances, be made of other materials, such as alloy steel or ceramic brick.

t In an alternative construction according to the invention, the'spiral metal-retaining trough, in-

trough assembly is preferably made up of acy- ,i

lindrical sleeve 3 6 which slides snugly into the still and to theinside of which the spiral strip 35 is welded. The sleeve and associated trough are preferably made up in a number of identical sections which are slipped into Athe still body through the top and are superposed within the vvaporizing section of the still to form a continuous spiral trough of any desired height. (One such section is shown in Fig. 2.)

In operation of the still of Figs. 2 and 3, the alloy feed is introduced into the' upper end of the trough 34 and circles downwardly through the still, being heated from the hot wall I6 and vaporizing its volatile component, The vapors rise through the open central core and escape into the .condenser I '1.

It is to be understood that the foregoing description is illustrative rather than strictly limitative, and that the invention is co-extensive in scope with the following claims.

What is claimed is:

1. In a still 4for the vacuum distillation of a volatile metal fromV a molten alloy thereof: a vertical elongated thermally-conductive closed still body having therein a vaporizing zone and a coninmaenesium from a source not densin-g zone in communication with each other.

. lng the still body at the vaporizing zone for raising the latter to a distilling temperature by heat applied externally to the still body, a conical pillar mounted axially in the still body Within the vaporizing zone and having formed in the outer surface thereof a shallow open spiral trough extending in a continuous downward slope from the upper to the lower part of the zone, means for introducing the alloy to be distilled into the upper part of the trough and for collecting residual alloy flowing from the bottom of the trough, and means for withdrawing condensate from the condenser.

2. A still according to claim 1 wherein the pillar is constructed of graphite. v

DOUGLAS S. CHISHOLM.

THOMAS GRISWOLD, JR.

REFERENCES CETED The following references are of record in the fue of this patent:

UNTED STATES PATENTS Number Name Date 55,071 Divine et al May 20, 1366 503,586 DuPont Aug. 22, 1893 780,475 Behrens Jan'. 17, 1905 l 1,219,413 Donk Mar. 13, 1917 1,899,916 Payne Feb. 28, 1933 2,239,371 Osborn Apr. 22, 1941 2,309,644 Hansgirg Feb. 2, 1943 2,337,042 Gloss Dec. 21, 1943 2,362,718 Pidgeon Nov. 14, 1944 2,391,728 McConica Dec. 25, 1945

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