US3042511A

US3042511A - Apparatus for condensation of a metal vapor

Info

Publication number: US3042511A
Application number: US792049A
Authority: US
Inventors: Jr John N Reding
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1959-02-09
Filing date: 1959-02-09
Publication date: 1962-07-03
Anticipated expiration: 1979-07-03

Description

y 1962 J. N. REDING, JR 3,042,511

APPARATUS FOR CONDENSATION OF A METAL VAPOR Filed Feb. 9. 1959 INVENTOR. John /V. Red/n Jr:

4 TTORNE Y 'United rates Fasten 3,042,511 Fatented July 3 1962 3,042,511 APPARATUS FUR CGNDENSATHQN @F A METAL VAPQR John N. Reding, 31:, Midland, Mich, assigns: to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Filed Feb. 9, H59, Ser. No. 792.,tl t9 6 Claims. (Cl. 75--67) This invention relates to an apparatus and a method for the condensation of metallic vapors. More particularly, it relates to an improved apparatus and method for abruptly chilling metallic vapors by use of a liquid quench.

In the thermal reduction of magnesium oxide with car bon and in the distillation or sublimation of volatile metals, such as magnesium, zinc, and aluminum, it is often desired to abruptly chill the metal vapors to a temperature considerably below the melting point of the metal. It is necessary to abruptly cool the product obtained by thermal reduction of magnesium oxide with carbon in order to prevent the reverse reaction from converting the magnesium back to magnesium oxide. A convenient method of abruptly chilling the metallic vapors or products is by quenching the product with a liquid. In quenching metallic vapors with a liquid at a sufficiently low quench temperature, the metal is condensed in fine particle size. Thus the quenching of metallic vapor with a liquid may be used as a simple method for the preparation of a metal in fine particle size.

In quenching of metallic vapors, a difiiculty is encountered of keeping the inlet to the quench chamber or the outlet from the furnace from becoming cooled. Ordinarily surfaces ahead of the quenching zone are cooled by the quenching liquid causing the metallic vapors issuing from the furnace to come into contact with these cooled surfaces and solidify. Upon solidification, the metal adheres to the cooled surface. Thus the condensing metal gradually builds up until the passageways ahead of the quench zone may become plugged. In most of the apparatus a reamer is provided which in frequent intervals, e.g. every 2 to 8 hours, is passed through the inlet to the quench chamber and the discharge tube of the furnace to remove the metal which has solidified at these points. Often it is necessary to shut down the equipment in order to remove the solidified metal. The elimination of the inconvenience of the metal solidifying ahead of the quench chamber is greatly desirable.

It is, therefore, an object of the invention to provide a method and an improved apparatus for abruptly cooling metallic vapors by quenching with a liquid medium wherein the metallic vapors issuing from the discharge line in the furnace do not solidify in the discharge line or in the inlet to the quench chamber; A further object is to provide a method and an apparatus for quenching metallic vapors wherein the metallic vapors may be abruptly chilled to a temperature considerably below the melting point of the metal to produce a metal product in submicron particle size.

Other objects and advantages will become apparent as the description of this invention proceeds, reference being had to the accompanying drawings in which:

FIGURE 1 diagrammatically shows a sectional elevation of the improved quenching apparatus.

FIGURES 2 and 3 are sectional views of the apparatus shown in FIG. 1 taken through planes 22 and 3-3, respectively.

FIGURE 4 shows a modification of the quenching apparatus of FIGURE 1.

In FIGURE 1, the quench apparatus is indicated generally by numeral 10. The apparatus comprises a cylindrical vessel ll vertically disposed. The wall of the upper portion is tapered inwardly to form a frustum shaped section 12 opened at the top to provide an inlet 13 to the vessel. The wall of the bottom portion is also tapered inwardly to form a frustum shaped section 14 open at the bottom to provide an outlet 16. While it is not necessary to have a conical shaped section at the bottom of the vessel, it facilitates removing from the apparatus the slurry obtained upon quenching the metallic vapors. A cylindrical shell 17 encompasses the upper portion 12. of the vessel. The bottom of the cylindrical shell is attached to the vessel as by welding and the top edge 18 of the shell extends above the top of the vessel. An annular deflection plate 19 is attached as by welding above the top of the vessel inside of the cylindrical shell :1 short distance below top edge 18 of the cylindrical shell. An opening 2% in the center of the deflection plate is aligned with inlet 13 of the vessel along its vertical axis. The top edge 21 of inlet 13 is spaced a short distance from the undersurface 2Q of the deflection plate so as to provide an opening or space 23 between the deflection plate 119 and the top edge of the inlet. The cylindrical shell 17, deflection plate 19, and the outer surface of Section 12 of the vessel form an annular duct 24 encompassing section 12 and the inlet 13 to the vessel with opening 23 serving as a passageway between the duct and inlet to the vessel. The annular space 24 has three tangential inlets 26, equally spaced around the periphery of cylindrical shell 17 as shown. In the quench section 25 of the vessel, below section 12, nozzles 27 extend into the vessel through which the quench liquid is introduced. The nozzles are disposed to direct the liquid downwardly and toward the vertical axis. Three nozzles are shown distributed equidistant around the periphery of the vessel. It is apparent that the number of nozzles to the quench section or inlets to the annular space 24 may be widely varied. They can be increased above 3 or reduced to only 1 inlet and 1 nozzle. The positioning of the nozzles and the inlets may be more clearly seen in FIGURES 2 and 3.

A flange 29 attached to the bottom of the vessel and surrounding outlet 16 may be used as a means of attaching to the quench apparatus a receiver (not shown) in which the slurry of the quenching liquid and metal particles are collected. At the top, a flange 31 around the periphery of the cylindrical shell 17 also serves as a means of attaching the apparatus to a furnace of which only a fragmentary portion is shown and indicated generally as 32. As shown the furnace has a corresponding flange 33 and is attached to the quench apparatus by use of bolts 34%. A discharge line 36 through which the vaporized metal is discharged from the furnace is directed downwardly and centered along the vertical axis of the quench apparatus. The discharge line is encased in insulation 37. Since deflection plate 19 is located within the cylindrical shell at a distance down from the top edge 18 of the cylindrical shell, a space 381 is provided between the top of the deflection plate and the bottom of flange 3-3 of the furnace discharge line.

In FIGURE 4, a modification of the apparatus is shown wherein the upper frustum shaped portion of the vessel is replaced by a cylindrical shell 4%) of reduced diameter with respect to the body or quenching zone 41 of the vessel. The portions of the vessel which are the same as the vessel shown in FIGURE 1 are identified by the same number as used in FIGURE 1.

In the operation of the apparatus, the nozzles 27 and inlets 25 to the annular duct 24 are connected to pipe lines supplying the quench liquid. The quench liquid is introduced through the tangential inlets 26 at suflicient rate to produce a flow of the liquid in the duct around the vessel. As the annular duct 24 becomes filled with liquid it will pass over the top edge 21 of inlet 13 at the top of the vessel with a swirling motion and pass down along the inner wall of the frustum shaped section 12 of the vessel. The swirling motion imparted to the liquid aids in obtaining complete coverage of the inner surface of the frustum shaped section 12 with the liquid. Thus, a moving liquid film on the inner wall of the upper frustum shaped section of the vessel is obtained. While it may not be necessary to have the inlet 26 tangentially located to provide the swirling motion for the liquid in annular duct 24, a more uniform liquid film and complete coverage of the inner wall of the vessel is more easily obtained by passing the liquid over edge 21 while it is moving in a circular path. The deflection plate 19 keeps the moving liquid from splashing on to the furnace flange 33 or the insulation around the discharge line 36, even though the space 23 between the deflection plate and top edge 21 of the inlet to the vessel may be sufficiently large so that the height of the liquid above edge 21 of the vessel would not normally contact the deflection plate. The quench liquid being introduced into the quench apparatus through nozzles 27 is directed downwardly and towards the center. The vaporized metal coming from a furnace (not shown) issues through line 36 directly along the vertical axis of the apparatus and passes into the vessel 11 through inlet 13. It passes through an intermediate zone or the frustum shaped portion of the vessel before discharging into the quench zone. In the frustum shaped portion 12, the velocity of the metallic vapor stream is sufficiently reduced by the enlargement of this portion of the vessel to obtain good contact with the quench liquid in the quenching zone. While passing through the frustum shaped portion 12 of the vessel, the metal particles which move out toward the wall contact the film of liquid passing over the surface and are carried down in the liquid film upon solidification. Consequently, it is essential that all of the surface inside of the vessel ahead of the spray nozzles be covered by a moving liquid film. Any area which is not covered with the liquid will result in the metal vapors contacting this area and upon solidification adhere to the surface. The volatile metals are good heat conductors. Once some of the metal has condensed on the surface of the vessel, it will continually build up until the apparatus becomes plugged unless prevented by the liquid film as provided by this apparatus.

In addition to slowing down the metallic vapor stream, the upper frustum shaped portion 12 of the vessels serves as a means of removing the quench zone of the apparatus from the immediate vicinity of the discharge line of the furnace or inlet without appreciably cooling the vapors. Since the discharge line of the furnace is located at a distance from the quench zone of the furnace, it is not cooled by the quenching. As the result, no solidification of the metal takes place at the furnace outlet.

Thus the metallic vapor issuing from the furnace is abruptly chilled by quenching the vapor to produce a sub-micron particle size product by passing the vapor from the furnace discharge line through an intermediate zone downwardly along the vertical axis of the zone before discharging the vapor into a quench zone. The walls of the intermediate zone in alignment with the direction of the metallic vapor flow are continuously washed with a quench liquid to have the surface of the walls adjacent to the flowing vapor completely covered with a moving film of the liquid. In the quench zone the vapor is contacted and abruptly chilled by a spray of quench liquid discharged into the quench zone.

The apparatus is particularly useful in a process where it is desirable to produce sub-micron sized particles of magnesium and sodium. To obtain sub-micron particles, it is essential to abruptly cool the metallic vapors. To a certain extent, the more rapidly the vapors can be cooled through the condensation temperature gradient the finer the condensed particles will be. While particles obtained on more gradual cooling may still be fine, they will generally be above micron size. Spray quenching is the most convenient way of obtaining the required fast cooling to produce submicron particle size. Spray quenching has a further advantage in that the particles of metal upon condensation are coated with droplets of oil. Thus the fine particles of the condensed metal are carried down with the droplets of oil. With other methods, the metal condenses to form a fine particle dust which is very difiicult to recover.

To condense the major portion of the metallic vapors in sub-micron size, a particle size of from .05 to .5 micron, it is desirable in quenching the vapor to use a large amount of quenching fluid. As the result a slurry is formed which may contain only a fraction of a percent of magnesium. It is costly to process a slurry of low concentration to recover the small amount of magnesium that it contains. Consequently, it is desirable to cool the slurry obtained from the quench apparatus and to recycle it until the concentration of the magnesium in the slurry approaches usually about 3 weight percent and at times considerably higher.

It is apparent that the apparatus may be modified in numerous ways without departing from the scope of the invention. The body of the vessel or the quench zone of the vessel may be of any cross-sectional shape. As shown it is cylindrical, but a square, rectangular, and the like may be used. The bottom portion of the vessel which is shown to be conical shaped or frustum shaped is made in this configuration to aid in draining the slurry from the vessel. This portion of the vessel may be made in any shape and does not play a significant part in the successful quenching of the metallic vapors to obtain the metal in sub-micron particle size without solidifying the metal ahead of the quench Zone. The duct surrounding the inlet to the vessel may also be of any shape. It is only necessary to have the quench liquid flowing over the top edge of the inlet so that a moving film of liquid may be obtained covering the inner surface of the upper portion of the vessel.

The inlet to the vessel and the opening in the deflection plate should be of suflicient size so as not to interfere with the vapor stream issuing from the furnace discharge line. The apparatus is operated under a reduced pressure with respect to the furnace so that the metal vapors discharge into the quenching vessel at an appreciable velocity. Since the vapors are traveling at an appreciable velocity, the stream will discharge a short distance from the end of the discharge line and into the vessel through inlet 13 without being unduly enlarged by deflection or the divergence of the stream. Consequently, the opening 20 of the deflection plate and inlet 1-3 of the vessel do not have to be very much larger than the discharge line of the furnace. However, generally the ratio of the diameter of the furnace line to the diameter of the openings of the deflection plate and the inlet to the vessel is in the range of 1:2 to 1:8, preferably in the range of 1:3 to 1:5. Openings having a diameter greater than 8 times the diameter of the discharge line is undesirable. The vapor stream as it enters the vessel creates eddy currents which may carry the metallic vapors from the vessel to the insulation surrounding the discharge line if the openings are too large. Solidification of the metal around the discharge line may thus become started.

While the upper portion of the vessel may be cylindrical in shape, as shown in FIGURE 4, a vessel having the upper portion shaped as a frustum as shown in FIGURE 1 is preferred. In a frustum shaped upper portion as shown in FIGURE 1, the currents created by the turbulence of the vapor stream entering the vessel may be more easily retained within the vessel without allowing them to leave the vessel through the opening and contacting the surface around the discharge tube of the furnace. With the upper portion of the vessel being cylindrical as shown in FIGURE 4, this portion of the vessel serves mainly as tion must be long enough to remove the quenching zone from the vicinity of the discharge line. However, it must not be too long or it will gradually substantially cool the 'vapor stream. The vapor stream may be sufiiciently cooled so that upon quenching the desired fine particles of the metal are not obtained. Thus, the velocity of the vapor stream will determine the optimum length for this particular section. Although a certain amount of flexibility is possible, there is a limit as to the length or height of the cylindrical upper portion which is desirable for a given velocity of the metallic vapor stream issuing from the discharge line.

Generally, when the upper portion of the vessel is not frustum shaped but cylindrical, the diameter of the upper portion is smaller than the quench portion of the vessel. In the quench section it is desired to have the area enlarged so that the velocity of the vapor is sufiiciently reduced to obtain good contact and mixing with the quench liquid sprayed into the vessel. The cross-sectional area required to obtain the required reduction in velocity is generally larger than 8 times the diameter of the furnace discharge line.

In a vessel having the upper portion frustum shaped, the slope or angle of the frustum shaped portion may be varied over a wide range. A frustum section such that the wall of the section tapers inwardly at the top or outwardly at the bottom to form an angle of from 20 to 45 degrees with respect to the vertical axis is generally preferred, with 30 degrees being the optimum. When the wall of the frustum shaped portion forms an angle greater than 45 degrees with respect to the vertical axis of the vessel, it may be difficult to maintain a liquid film on the underside of this portion of the vessel. With the angle being less than 20 degrees, the slope of the frustum shaped portion is small enough so that its operational characteristics approach those of a cylindrical section as discussed above.

An apparatus similar tothat shown in FIGURE 1 was used in quenching of magnesium vapors for the production of magnesium in a fine particle size. The quench apparatus was attached to a downwardly projecting discharge line from an electric furnace in a manner similar to that shown in FIGURE 1. The discharge line was a graphite tube of about 2 inches in diameter. Magnesium was charged to the furnace where it was heated or vaporized at a rate such that approximately 20 pounds per hour of magnesium vapor discharged into the quench apparatus. The vapors were drawn into the quench chamber from the furnace by maintaining a reduced pressure in a receiver to which the quench apparatus was attached.

The quench apparatus had an overall length or height of approximately 31 inches with the quench zone being about 18 inches in diameter. The upper portion of the vessel was frustum shaped with walls tapering in to form an angle of 30 degrees with respect to the vertical axis of the vessel. This upper portion was approximately 9 inches in height or length. The opening in the deflection plate and the top of the vessel was approximately 8 inches in diameter. The duct surrounding the opening of the vessel was provided with one tangential entry. The

quench zone was equipped with 3 fiat spray nozzles symmetrically spaced around the periphery of the vessel. In the operation of the apparatus, 11 gallons per hour of a jet engine fuel oil, referred to as JP-4 under United States Government specifications, were charged through the tangential entry into the duct. The fuel oil was passed over the edge of the inlet to the vessel and as a moving film flowed down the inside of the frustum shaped portion of the vessel. In the quench zone, 13 gallons per hour of the fuel oil was sprayed into the vessel through the three nozzles. The slurry obtained upon quenching was cooled and recycled through the spray nozzles and the upper portion of the vessel until a slurry containing approximately 2 weight percent of magnesium was obtained. ,When a slurry of this concentration was obtained, a portion was withdrawn to recover the magnesium while make-up fuel oil was added.

In a continual operation of 11 hours, a total of pounds of magnesium was recovered. The magnesium obtained was in sub-micron particle size between .05 to .3 micron. No plugging of the discharge line or to the entry of the quench chamber was obtained. After the run, the quench chamber was inspected. No noticeable amount of magnesium had condensed around the discharge line of the furnace or the entry to the vessel.

What is claimed is:

1. An apparatus for the condensation of a metal vapor used in conjunction with a vaporization furnace, which comprises a vessel vertically disposed having an opening at the bottom and an opening at the top, an annular duct encompassing the opening at the top, said duct having a continuous open passageway at the top around the top edge of the opening of the vessel communicating with the vessel, at least one inlet into said duct, at least one nozzle into said vessel located at a distance from the top of the vessel, said nozzle having openings directed downwardly and toward the center of said vessel, means to attach the vessel to the vaporization furnace with the discharge of the furnace being aligned to discharge downwardly into the vessel along the vertical axis of the vessel, and means for the introduction of an inert cooling fluid into said nozzle and inlet to said duct.

2. An apparatus for the condensation of a metal vapor used in conjunction with a vaporization furnace, which comprises a vessel vertically disposed having an outlet at the' bottom, said vessel having the wall in the upper portion tapered inwardly to form a frustum shaped section opened at the top with the opening being centered with respect to the vertical axis of said vessel, an annular duct encompassing the opening at the top of the vessel, said duct having a continuous open passageway at the top around the top edge of the opening of the vessel communicating with the vessel, at least one inlet into said duct, at least one nozzle in said vessel located below the frustum shaped section, said nozzle having openings directed downwardly and toward the center of said vessel, means to attach the vessel to the vaporization furnace with the discharge of the furnace being aligned to discharge downwardly into the vessel along the vertical axis, and means for the introduction of an inert cooling liquid into said nozzle and inlet to said duct.

3. An apparatus for the condensation of a metal vapor used in conjunction with a vaporization furnace, which comprises a cylindrical vessel vertically disposed having an opening at the bottom, said vessel having the wall in the upper portion tapered inwardly to form a frustum shaped section opened at the top with the opening being centered with respect to the vertical axis of the vessel, an annular duct encompassing the opening at the top of the vessel, said duct having a continuous passageway at the top communicating with the vessel around the top edge of the opening of the vessel, at least one inlet directed tangentially into the duct at the outer periphery of the duct, at least one nozzle extending through the wall of said housing located below said frustum shaped section, said nozzle having openings directed downwardly and toward the vertical axis of said housing, means to attach said apparatus to the vaporization furnace with the discharge of the furnace being aligned to discharge downwardly into the opening at the top of vessel, and means for introduction of an inert cooling medium into said nozzle and the inlet to said duct.

4. An apparatus according to claim 3 wherein the Wall 7 of the frustum shaped section tapers inwardly so as to form an angle of 30 degrees with respect to the vertical axis.

5. In a process for abruptly cooling of a metal vapor to solidify the metal in a sub-micron particle size wherein the metal vapor is discharged from a vaporization furnace through a discharge line into an enlarged quench zone and :a liquid is sprayed into the quench zone, the step to prevent the solidification of the metal on surfaces ahead of the quench zone which comprises passing the metal vapor from the furnace discharge line downwardly into an intermediate zone prior to discharging the vapor into the quench zone, said intermediate zone being encircled by a falling film of quench liquid covering the walls of the intermediate zone.

6. A process accordingto claim 5 wherein the metal is magnesium.

References Cited in the file of this patent UNITED STATES PATENTS 1,800,356 Powell Apr. 14, 1931 2,109,841 H-ansging Mar. 1, 1938 2,238,909 McConioa Apr. 22, 1941 2,416,255 Griswold et a1 Feb. 18, 1947 2,430,389 Chubb Nov. 4, 1947 2,433,434 Church Dec. 30, 1947 2,477,420 Rhoades July 26, 1949 2,631,019 Yates Mar. 10, 1953 FOREIGN PATENTS 600,026 Great Britain Mar. 30, 1948

Claims

5. IN A PROCESS FOR ABRUPTLY COOLING OF A METAL VAPOR TO SOLIDIFY THE METAL IN A SUB-MICRON PARTICLE SIZE WHEREIN THE METAL VAPOR IS DISCHARGED FROM A VAPORIZATION FURNACE THROUGH A DISCHARGE LINE INTO AN ENLARGED QUENCH ZONE AND A LIQUID IS SPRAYED INTO THE QUENCH ZONE, THE STEP TO PREVENT THE SOLIDIFICATION OF THE METAL ON SURFACES AHEAD OF THE QUENCH ZONE WHICH COMPRISES PASSING THE METAL VAPOR FROM THE FURNACE DISCHARGE LINE DOWNWARDLY INTO AN INTERMEDIATE ZONE PRIOR TO DISCHARGING THE VAPOR INTO THE QUENCH ZONE, SAID INTERMEDIATE ZONE BEING ENCIRCLED BY A FALLING FILM OF QUENCH LIQUID COVERING THE WALLS OF THE INTERMEDIATE ZONE.