METHOD AND APPARATUS FOR LIQUID METAL COLLECTION FROM VAPOR USING MOLTEN POOL OF COLLECTING METAL

Abstract: A metal vapor, such as can be produced by sublimation of crudely smelted lumps of the metal at high temperature, is led, at a high enough temperature and a low enough pressure for the condensation of the vapor not to take place, into the upstream end of a convergent-divergent nozzle, and then squirts out from this nozzle, being cooled down rapidly by adiabatic expansion in the nozzle to a low enough tempera­ ture for the condensation of the vapor to take place. The jet flow emitted from the downstream end of the convergent-­ divergent nozzle, which has been thus cooled, is led to the surface of a pool of molten collecting metal, either directly or via a jet flow decelerating device. The collecting metal in this collecting metal pool is the same kind of metal as the metal vapor which is to be collected. This the condensed metal vapor in the jet flow is entrained into the collecting metal pool in the liquid state. Apparatuses are also disclosed for perform­ ing these various methods.

Description: BACKGROUND OF THE INVENllON The present invention relates to a method for collecting metal in the liquid state from a metal vapor, and to a device for practicing said method, and more particularly relates to a method for collecting, from a metal vapor which has been produced by sublimation of crudely smelted lumps of said metal at a high temperature, said metal vapor in a liquid state, and to a device for practicing said method. A known method of preparing a metal in the pure state is to smelt the metal (as for example from its oxide) in a rough manner, thus producing a rather impure form of the metal including for example impurities such as remaining oxide, and then to subject this raw material to a low pressure at a high temperature. At such a high temperature the metal is sublimated in the pure form in the state of metallic gas or vapor, and thus the question arises as to how the metal vapor can be quickly cooled down and reduced into the liquid phase, which is the most convenient for handling and post processing such as formation into ingots or the like. In the case of metals such as for example lead and zinc, which have relatively low melting points, there has been practiced a prior art collectal method in which the high temperature metal vapor has been introduced into a condenser containing a mass of molten metal having a fairly low temperature which is lower than that of the metal vapor, and in which the metal vapor has been condensed into liquid by the molten metal being contacted intimately with the metal vapor by being splashed with a stirrer or paddle or impeller or the like. Thereby, the metal vapor is rapidly cooled and is picked up by the molten metal. As a variation of this prior art method, it has been known for the condenser to be shaped as a U-shaped tube, with the molten metal for collecting contained in the bend of the tube, and for the metal vapor to be blown around this U-shaped tube, being bubbled through the molten metal for collecting. This prior art method is unfortunately not so suitable for collecting the vapors of metals such as magnesium and calcium (for example) which have high melting points; and further it has The disadvantage that in order well to promote the quick condensation of the metal vapor either the size of the condensation chamber has been required to be rather large, possibly including fins or the like for increasing the contact area between the collecting molten metal and the metal vapor, or alternatively as explained above a paddle or stirrer or an impeller such as a fan has been required, with an associated external power source, in order to physically stir up the molten collecting metal and the metal vapor, so as to provide appropriate cores or seeds for liquefaction of the metal vapor. This is troublesome and expensive to provide, since the apparatus is at quite high temperature, and accordingly various constructional difficulties arise, which can only be overcome at considerable expense. SUMMARY OF THE INVENTION Accordingly, in view of the above problems, it is the primary object of the present invention to provide a method of collecting metal vapor in the liquid form, which effectively performs such collecting. It is a further object of the present invention to provide such a method of collecting metal vapor in the liquid form, which does not require any mechanical means for promoting the condensation and liquefaction of the vapor, such as a stirrer or paddle. It is a further object of the present invention to provide such a method of collecting metal vapor in the liquid form, which can be continuously practiced. It is a further object of the present invention to provide such a method of collecting metal vapor in the liquid form, which provides collected metal of high purity. It is a further object of the present invention to provide such a method of collecting metal vapor in the liquid form, which collectes a high proportion or ratio of the metal vapor. It is a yet further object of the present invention to provide such a method of collecting metal vapor in the liquid form, which is of acceptably low cost. It is a yet further object of the present invention to provide such a method of collecting metal vapor in the liquid form, which is suitable for collecting vapor of metals such as magnesium or calcium which have relatively high melting points. It is a yet further object of the present invention to provide an apparatus, for practicing a method which achieves one or more of the above mentioned objects of the present invention. According to the present invention, these and other objects relating to a method are accomplished by a method of liquid metal collection from vapor, wherein: said metal vapor is led, at a temperature and a pressure at which it does not condense, into the upstream end of a convergentdivergent nozzle; and the jet emitted from the downstream end of the convergent-divergent nozzle, which has been cooled rapidly by adiabatic expansion in said convergent-divergent nozzle to a low enough temperature for the metal vapor to condense, is led to the surface of a pool of molten collecting metal which is the same kind of metal as the metal vapor. According to such a method, when the jet is led to the molten collecting metal, the metal in the jet, which has been condensed by the rapid adiabatic temperature drop in the convergent-divergent nozzle either to small liquid droplets or to fine powder particles, is entrained directly into the molten collecting metal pool and is accumulated therein, in the liquid phase. Accordingly, the collecting is effectively performed. This process is very suitable for being continuously practiced, and provides collected metal of high purity. Further, this method can collect a high proportion or ratio of the metal vapor, with little loss, and at acceptably low cost. The method outlined above is particularly suitable and useful for collecting vapor of a metal such as magnesium or calcium, which has a high melting point. Also, because the metal vapor is not collected as a solid mass on a collecting plate or the like, no risk is run that the jet from the convergent-divergent nozzle should blow away a part of the collected metal from said solid metallic mass, and the metal is collected in a suitable form for post processing such as for formation into ingots, i.e. the molten form, and does not require any remelting. Further, according to the present invention, the abovementioned method is effectively performed by an apparatus for liquid metal collection from vapor, comprising: a gas tight housing means which defines a metal vapor supply chamber for supplying metal vapor at a temperature and a pressure at which it does not condense, and a collecting chamber for accomodating a pool of molten collecting metal of the same kind as said metal vapor; a convergent-divergent nozzle leading from said metal vapor supply chamber to said collecting chamber; means for heating said mixture supply chamber to said temperature and said collecting chamber to a temperature sufficient to hold said pool of molten collecting metal in the molten state; and means for depressurizing the interior of said housing means so that the interior of said mixture gas supply chamber is kept at said pressure. BRIEF DESCRIPI1ON OF THE DRAWING The present invention will now be shown and described with reference to the preferred embodiment of the method and the apparatus thereof, and with reference to the illustrative drawing. It should be clearly understood, however, that the description of the embodiment, and the drawing, are given purely for the purposes of explanation and exemplification only, and are not intended to be limitative of the scope of the present invention in any way, since the scope of the present invention is to be defined solely by the legitimate and proper scope of the appended claims. The sole figure of the drawing is a schematic structural diagram, showing the preferred embodiment of the apparatus according to the present invention for collecting metal vapor as a liquid using a collecting metal pool, which practices the preferred embodiment of the method for collecting metal vapor as, a liquid using a collecting metal pool according to the present invention. DESCRITTION OF ThE PREFERRED EMBODIMENTS The present invention will now be described with reference to the preferred embodiment of the apparatus and the preferred embodiment of the method thereof, and with reference to the appended drawing. THE CONSTRUCTION OF THE PREFERRED APPARATUS EMBODIMENT In the drawing there is shown a schematic structural view of an apparatus for collecting metal in the liquid phase from vapor of the metal which has been sublimated, according to the preferred apparatus embodiment of the present invention, which is used for practicing the preferred embodiment of the method for collecting metal in the liquid phase according to the present invention. In this figure, the reference numeral 1 generally denotes a sublimation furnace which is substantially formed as a closed container, which has a furnace body 3 provided with a layer 2 of insulating material; and a sublimation furnace chamber 4 is defined as a cavity within this sublimation furnace 1. A heater 5 is embedded in the wall of the furnace chamber 4, generally around said furnace chamber 4 and within the layer 2 of insulating material, so as to heat up the furnace body 3 and said furnace chamber 4 defined therein with said layer 2 of insulating material providing an insulation function. In the upper end wall 6 of the furnace chamber 4 there is provided a sublimation material charging port 7, to which is connected the lower end of a sublimation material charging hopper 8, the upper end of which is connected to a charging intake 11. Two control valves 9 and 10 are provided, respectively between the upper end of the charging hopper, 8 and the charging intake 11 and between the lower end of the charging hopper 8 and the charging port 7, so that by opening and closing these control valves 9 and 10 in an alternating fashion as will be easily understood by one of ordinary skill in the art material for sublimation may be charged into the sublimation furnace chamber 4 through the charging port 7 without substantially deteriorating the gas tight condition of the, sublimation furnace chamber 4. A charged mass of such sublimation material is, shown in the sublimation furnace chamber 4 and is denoted by the reference numeral 12. In the side wall 13 of the furnace chamber 4 there are provided two sublimation residue discharge ports 14 which lead 'residue accumulation hoppers 15 the outlets of which are controlled by valves; in fact, again, a similar double valve arrangement is provided for discharginge from time to time sublimation residues such as schematically indicated in the figure as 12t which are produced in the chamber 4 of the furnace 1 by sublimation (as will be explained later) through these sublimation residue discharge ports 14 without deteriorating the gas tight condition of the sublimation furnace chamber 4, although this is not shown in the figure. The bottom 17 of the sublimation furnace chamber 4 has a metal vapor conduit 18 set therein, the upper end of which opens to the interior of the sublimation furnace 4 with the interposition of a particle trap construction 16, so as to communicate the furnace chamber 4 with a metal vapor collecting chamber 21 provided below the furnace chamber 4 within the body of a metal vapor collecting furnace 20. Particularly according to an important principle of the present invention, the downstream end of this conduit 18 is formed as a convergent-divergent nozzle or Laval nozzle 22, which opens substantially vertically downwards (in this shown preferred embodiment) into said metal vapor collecting chamber 21. The particle trap construction 16 is shaped as a cap or hood, and includes a plurality of filters 19 for intercepting and capturing fine powder impurities in the metal vapor which is passing through them. Within the lower part of the metal vapor collecting chamber 21, below and opposed to the lower end of the convergent-divergent nozzle 22, there is provided a collecting metal pot 25, within which there is present during operation of the apparatus a pool 24 of molten collecting metal. This melting pot 25 is provided with a heater 26. The lower part of the metal vapor collecting chamber 21 is communicated, via a molten metal take out port 30 and via a molten metal take out conduit 32 which is controlled by a control valve 31, to a ladle 33 for removing molten metal. A slag take out port not shown in the figure is also provided for removing slag from the surface of the pool 24 of molten collecting metal in the melting pot 25 in the collecting chamber 21. A vacuum port 27 is communicated, via a conduit 28 and a control valve, to a vacuum pump 29, for evacuating the interior parts of the apparatus as a whole to appropriate vacuum levels, as will be more particularly described later. Particularly according to a particular feature of this preferred apparatus embodiment of the present invention, the central axial line 34 of the convergent-divergent nozzle 22 extends in the metal vapor collecting chamber 21 substantially vertically, so that as explained later during operation of the nozzle 22 the spray or jet flow 35 of metal vapor from said nozzle 22 should impact substantially at right angles onto the surface of the pool 24 of molten collecting metal in the melting pot 25. THE GENERAL OPERATION OF THE PREFERRED APPARATUS EMBODIMENT The shown apparatus according to the preferred embodiment of the apparatus of the present invention is generally used as follows. First, raw material for sublimation of an appropriate sort for producing vapor of a metal which is required to be refined as will be understood in detail later is charged into the furnace chamber 4 of the sublimation furnace 1, by charging this raw material into the charging hopper 8 through the charging intake 11, and by then opening and closing the control valves 9 and 10 in an alternating fashion as outlined above so as to transfer this raw sublimation material through the charging hopper 8 into the furnace chamber 4 without allowing gas from the outside to enter the furnace chamber 4 in substantial amount. Then the vacuum pump 29 is operated so as to depress the pressure within the apparatus, and the heater 5 is operated so as to heat up the furnace chamber 4 and the raw sublimation material charged therein to a predetermined temperature T1, so as to cause the charged sublimation raw material to emit metal vapor of the metal which is to be refined, said metal vapor being at a pressure P1 and possibly including dust or other powder type impurities blown up from said sublimation raw material. This metal vapor then passes in the heated state as shown by the arrows in the figure through the particle trap construction 16 of the sublimation furnace 1, which appropriately intercepts said dust or other solid impurities if any are present, and is then ejected from the furnace chamber 4, according to the difference of pressures between the interior of the furnace chamber 4 which is at said pressure P1 and the interior of the metal vapor collecting chamber 21 which is kept at a pressure P2 substantially lower than the pressure P1, through the conduit 18 and through the convergent-divergent nozzle 22 at the downstream end of said conduit 18, into the metal vapor collecting chamber 21, and sprays out of the convergent-divergent nozzle 22 as a jet 35 which impinges against the surface of a pool 24 of molten collecting metal, which is the same metal as the metal of the metal vapor which is to be collected, in the melting pot 25 placed at the bottom of said collecting chamber 21. As this metal vapor passes through the convergentdivergent nozzle 22, it reaches a supersonic speed and expands adiabatically very quickly, and thus the metal vapor is very quickly cooled down by thisCadiabatic expansion to a second temperature T2, which is envisaged to BbSwell below the condensation temperature of said metal vapor, and thus may be at least partly condensed into fine metal droplets or particles. The jet 35 including cooled metal vapor (in fact supercooled vapor) and/or possibly fine particles of liquid or solid metal thus produced impinges on the surface of the pool 24 of molten collecting metal in the melting pot 25 at the bottom of said collecting chamber 21, in this preferred embodiment substantially perpendicularly, and the metal in said jet 35 becomes mixed with and entrained into the molten collecting metal. The collecting chamber 21 and the sublimation furnace chamber 4 are maintained at their pressures P1 and P2 by the pump 29 being operated as and when necessary, so that metal vapor is sucked out of said collecting chamber 21, via the port 27 and the conduit 28. The sucking rate of the pump 29 thus is controlled so as to maintain the pressures in the sublimation furnace chamber 4 and in the metal vapor collecting chamber 21 at substantially their respective desired values P1 and P2, according of course also to various other parameters of the apparatus and its operation; but in fact this operation of the vacuum pump 29 may only be required when starting up the apparatus, and not during its steady operation. However, inevitably it may be the case that a small amount of gas is evolved from the heated raw sublimation material 12 which is being refined in the sublimation furnace chamber 4, and this gas will pass through the convergent-divergent nozzle 22 and thus will be required to be evacuated from the condensation chamber 21 by the vacuum pump 29, either continuously or intermittently. Further, as a practical matter during the steady operation of the apparatus it may not be necessary to continually operate the heater 26 for keeping the pool 24 of molten collecting metal in the melting pot 25 in the molten state, since the release of the latent heat of the metallic vapor from the jet 35 from the convergent-divergent nozzle 22 may provide sufficient heat for that purpose. From time to time, some of the collecting molten metal pool 24 in the melting pot 25 at the bottom of the metal vapor collecting chamber 21, with an amount of the sublimed and collected metal from the jet 35 entrained therein, is removed via the port 30 and the conduit 32 by operation of the valve 31 into the ladle 33, without disturbing the depressurized state of the apparatus. Further, from time to time, some of the slag in the bottom portion of the furnace chamber 4 is removed by operation of the above described (but not shown) means, again without disturbing the depressurized state of the apparatus; and also slag on the surface of the molten metal pool 24 may be removed. DESCRIPTION OF THE PREFERRED METHOD EMBODIMENT The preferred apparatus embodiment of the present invention described above was operated by charging a mass of lumps of raw refined magnesium with a small amount of impurities therein (which in fact was made by roughly smelting magnesium oxide) as a raw material for sublimation into the furnace chamber 4 of the sublimation furnace 1, by operating the vacuum pump 29, by operating the heater 5, by charging magnesium metal into the melting pot 25 of the metal vapor collecting chamber 21 and by melting this collecting magnesium metal into a pool 24 of collecting metal by operating the heater 26 for collecting the magnesium produced by sublimation in the sublimation furnace 1. Thus, the collecting metal (magnesium) used for the collecting metal pool 24 was the same metal as the metal (magnesium) which was to be collected. The temperature T1 to which the furnace chamber 4 and the raw sublimation material charged thereinto were heated was 900 C, and the rate of suction of the vacuum pump 29 was controlled so as to keep the pressure P1 within the sublimation furnace chamber 4 at approximately 80 to 10û torr and so as to keep the pressure P2 within the metal vapor collecting chamber 21 at approximately 15 to 20 torr. The second heater 26 was so operated as to maintain the temperature within the molten collecting magnesium metal pool at about 680 to 700 C, and thus so as to keep said collecting metal pool 24 of magnesium metal therein in the molten state. As explained above, the raw refined magnesium in lump form in the sublimation furnace chamber 4 of the sublimation furnace 1 was sublimated, so as to produce metallic magnesium in vapor form, thd this magnesium vapor then flowed out through the conduit 18 and through the convergent-divergent nozzle 22 into the metal vapor collecting chamber 21, attaining a supersonic speed as it passed through. the convergent- divergent nozzle 22. The jet flow 35 thus produced was quickly cooled down by adiabatic expansion in the nozzle 22 to below the temperature of condensation of the magnesium vapor, and impinged against the surface of the molten collecting magnesium metal pool 24 within the melting pot 25 in the metal vapor collecting chamber 21, and the magnesium vapor¯ (which¯ in fact was at this time either supercooled or partially liquefied and/or solidified) in said jet flow was entrained into and mixed with the molten magnesium metal pool 24. The entrained magnesium was then of course brought to the liquefied state by this entrainment into the collecting metal pool 24, and remained ^ therein. The magnesium in the pool 24 was removed from the apparatus from time to time as explained above. The depression of the liquid surface of the pool 24 of molten collecting magnesium metal was about 50 mm. The physical condition of the raw material charged into the sublimation furnace chamber 4 was lump briquette. The nature of this raw sublimation material was 92% Mg metal (the product of raw smelting as explained above). The throat diameter of the convergent-divergent nozzle 22 was 25 mm. The average pressure in the sublimation furnace 4 was 92 torr. The average pressure in the condensation furnace chamber 21 was 18.2 torr. The collecting ratio was 99.6%. The average purity of the collected magnesium was 99.93%. The results described above of operating the preferred embodiment of the apparatus of the present invention according to the preferred embodiment of the method of the present invention show that, even in the case of a metal such as magnesium, which has a relatively high melting point, a good result of collecting metal vapor which has been sublimated can be obtained, with a purity and a collecting ratio both close to 100%. The pool 24 of molten collecting metal in the melting pot 25 may be initially provided by either (a) placing an initial supply of metal (which as stated above is to be the same as the metal the vapor of which is being sublimated for collection) in said melting pot 25 before sealing the apparatus; or (b) by directly collecting in the bottom of the melting pot 25 some metallic vapor from the jet flow 35 from the convergent-divergent nozzle 22 in the initial phase of operation of the apparatus; or (e) by melting some metal which is collected from the metallic vapor from the jet flow 35 from the convergent-divergent nozzle 22 by a capturing plate or the like as a solid metal mass, by the use of the heater 26. Although the present invention has been shown and described with reference to the preferred embodiment of the method and the device thereof, and in terms of the illustrative drawing, it should not be considered as limited thereby. Various possible modifications, omissions, and alterations could be conceived of by one skilled in the art to the form and the content of any particular embodiment, without departing from the scope of the present invention. For example, although the present invention has been described with regard to collecting metal vapor which has been obtained from magnesium metal produced by rough smelting, this should not be considered as limitaive of the scope of the invention, which is applicable to other materials as well as to magnesium. Therefore it is desired that the scope of the present invention, and of the protection sought to be granted by Letters Patent, should be defied ?,f t8;e. perhaps purely fortuitous details of the shown embodiment, or of the drawing, but solely by the scope of the appended claims, which follow.

Claims: WHAT Is CLAIMED Is: 1. A method of liquid metal collection from vapor, wherein: said metal vapor is led, at a temperature and a pressure at which it does not condense, into the upstream end of a convergent-divergent nozzle; and the jet emitted from the downstream end of the convergent-divergent nozzle, which has been cooled rapidly by adiabatic expansion in said convergent-divergent nozzle to a low enough temperature for the metal vapor to condense, is led to the surface of a pool of molten collecting metal which is the same kind of metal as the metal vapor. 2. A method according to claim 1, wherein said jet is directed directly against said surface of said pool of molten collecting metal. 3. A method according to claim 1, wherein said metal vapor and said collecting metal are both magnesium. 4. An apparatus for liquid metal collection from vapor, comprising: a gas tight housing means which defines a metal vapor supply chamber for supplying metal vapor at a temperature and a pressure at which it does not condense, and a collecting chamber for accomodating a pool of molten collecting metal of the same kind as said metal vapor; a convergent-divergent nozzle leading from said metal vapor supply chamber to said collecting chamber; means for heating said mixture supply chamber to said temperature and said collecting chamber to a temperature sufficient to bold said pool of molten collecting metal in the molten state; and means for depressurizing the interior of said housing means so that the interior of said mixture gas supply chamber is kept at said pressure. 5. An apparatus according to claim 4, wherein the central axis of said eonvergent-divergent nozzle is substantially vertically arranged and the outlet of said eonvergent-divergent nozzle is directed downwardly toward said collecting chamber.

Inventors: MIURA, HIROHISA, NATSUME, TOSHIO, SATOU, HIROSHI
Applicants: TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1983
Main classification: C22B5
IPC codes: C22B26, C22B5, B01D7