Note: Descriptions are shown in the official language in which they were submitted.
~11! 93
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BACKGRC)UND OF THE INVENTIO~
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 produclng
0 Q 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
lS 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
we~l 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
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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 variGus 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 met~l 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
lo~ 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
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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 met~l 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
li~uid phase. Accordingly, the collecting is effectively performed. This
process is very suitable for being continuously practiced, and provides
co11ected 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.
~urther, according to the present invention, the abovementioned
method i5 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 rnolten coilecting metal of the same kind as said
metal vapor; a convergent-divergent nozzle leading from said metal vapor
supply chamber to said collecting chamber; me~ns for heating said mixture
supply chamber to said temperature and said collecting chamber to a
temperature suPficient 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.
932
BRIEF DESCRIPlION OF THE DRAW~NG
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.
D~;CRIPIION O~ THl~ PREFERRED EMBODIMENTS
The present invention will now be described with reference to the
preferred embodiment of the apparatus and the preferred embodiment of
j- 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 l. A heater 5 is
embedded in the wall of the furnace chamber 4, generally around said
furnece 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
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of a sublimation material charging hopper 8, the upper end of which is
connected to a charging intake llo 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
5 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
10 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 to residue
accumulation hoppers lS the outlets of which are controlled by valves; in
15 fact, again, a similar double valve arrangement is provided for discharging
from time to time sublimation residues such as schematically indicated in
the figure as 12' 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
20 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
25 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 su~stantially vertically downwards (in this shown preferred
30 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,
35 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
12~ 93~
during operation of the apparatus a pool 24 of molten collecting metal.
This melting pot 25 is provided with a heater 26. The lower pnrt 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
5 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 2~ and a control valve, to a vacuum pump 29,
10 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
15 chamber 21 substantially vertically, so that as explained later during
operation of the noz~le 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 P~EFERRED APPARATUS
20 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
25 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
30 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
35 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
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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
5 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 Pl and the interior of the metal vapor collecting
chamber 21 which is kept at a pressure ~2 substantially lower than the
pressure Pl, through the conduit 18 and through the convergent-divergent
10 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
15 collecting chamber 21. As this metal vapor passes through the convergent-
divergent nozzle 22, it reaches a supersonie speed and expands
adiabatically very quickly, and thus the metal vapor is very quickly cooled
down by this adiabatic expansion to a second temperature T2, which is
envisaged to be well below the condensation temperature of said metal
20 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
25 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
30 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 Pl and P2, according of
35 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
12~(~93~
when starting up the apparatus, and not during ;ts steady operation.
However, inevitably it may be the case that a small amount of gas is
evolved from the heated raw suMimation material 12 which is being refined
in the sublimation furnace chamber 4, ancl this gas will pass through the
S convergent-divergent nozzle 2~ and thus will be required to be evacuated
from the condensation chamber 21 by the vaeuum pump 29, either
continuously or interrnittently. 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
10 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,
15 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
20 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
25 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
30 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 2~, 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
35 the same metal as the metal (magnesium) which was to be collected. The
temperature Tl to which the furnace chamber 4 and the raw sublimation
- 10 ~ '932
material charged thereinto were heated WAS 900C, and the rate of suction
of the vacuum pump 29 was controlled so as to keep the pressure Pl within
the sublimation furnace chamber 4 at approximately 80 to 100 torr and so
as to keep the pressure P~ within the metal vapor collecting chamber 21 at
approximately 15 to 20 torr. The second heater 26 was so operated as to
main~ain the temperature wi~hin the molten collecting magnesium metal
pool at about 680 to 700C, and ~hus 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, and 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 li~uid 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
S 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 twhich as
stated above is to be the same as the metal the vapor of which is being
10 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 metall;c vapor from the jet flow 35 from the convergent-divergent
no~zle 22 in the initial phase of operation of the apparatus; or (c) by
melting some metal which is collected from the metallic vapor from the
15 jet flow 35 from the convergent-divergent nozzle 22 by a capturing plate
or the like as a solid metPl 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
20 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
25 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 defined not by any of the
30 perhaps purely fortuitous details of the shown embodiment, or of the
drawing, but solely by the scope of the appended claims, which follow.
