US2781189A - Apparatus for condensing metals to the liquid state - Google Patents

Description

APPARATUS FOR CONDENSING METALS TO THE LIQUID STATE Filed March 10, 1955 2 Sheets-Sheet l INVENTOR Pie rr'e L.Camescas se d Michel L.Pec1t ATTORNEY Feb. 12, 1957 P. CAMESCASSE EI'AL Filed March 10, 1953 2 Sheets-Sheet 2 W k m g 1O 1 5 A I l 2A "12 22;= E Q A 25 7-- /2o A 5: E *5 g" i i 2 *1 o N o INVENTOR Pierre Lcamescasse d Michel L.Petii ATTORNEY United States Patent APPARATUS FOR CONDENSING METALS T THE LIQUID STATE Pierre Camescasse and Michel Petit, Bagneres-de-Bigorre, France, 'assignors to Soberma (Societe de Brevets dEtudes et de Recherches pour le Magnesium), Paris, France, a corporation of France Application March 10, 1953, Serial No. 341,453

Claims priority, application France March 17, 1952 7 Claims. (Cl. 266-) In numerous producing or distilling apparatus which produce a metal in the condition of a vapor, it is advantageous to condense the metal to a liquid rather than to a solid state. Its removal is then easier and losses due to combustion are smaller.

However, it has been observed that, unless specialprecautions be taken, yields may be considerably lower when the metal is condensed to the liquid state, especially when the condensation takes place in a vacuum.

In particular, in furnaces for producing metals by thermal reduction, for example, in the production of magnesium, it has been found that radiation by the furnace and the output of metal vapor are very variable with time; as a result, large variations in the temperature of the condensing chamber are noticeable.

In the case where the metal is condensed to the solid state, these temperature changes are generally insufficient to cause appreciable losses during the condensation. In fact, since the condenser is intensely cooled, the temperature of the condensed metal is very low and the walls of the condensing chamber are always at a higher temperature so that the metal does not deposit thereon.

The circumstances are difierent when condensation takes place to the liquid state. The temperature of the metal on the condensing surface is very close to the triple point of the metal. When the condensing surface is located within the inner space of the condensation chamber, it is necessary that all the walls of the condensing chamber be kept at a temperature above this point, almost above the dew point at the pressure used.

Unless this be done, the metal deposits on these walls in a finely divided condition. If it be highly oxidizable, it catches fire when the condensing chamber is opened, but in any exent, it is soiled and diflicult to recover, so that the condensation yield is greatly diminished.

To avoid this drawback, it has been proposed to place the condensation chamber in the immediate vicinity of the production furnace, and to connect them by a duct of large cross-section so as to utilize the waste heat of the furnace to keep the walls of the condensing chamber at the required temperature. However, the adoption of these expedientsoften highly inconvenientare not sufficient to prevent condensation of metal on the walls during those periods when radiation from the furnace is small.

The present invention, based on the investigations of the applicants, makes it possible to avoid these drawbacks and to obtain the condensation of metals to the liquid state with an excellent yield.

The invention relates to a process for condensing metals in a vacum to the liquid state, in which variable amounts of calories are supplied within the condensing chamber, so as to maintain the temperature of the inside walls of this chamber on which the metal is condensed between the melting point and the dew point of said metal at the vacuum used, whatever he the instantaneous rate of flow of the vapors to the condenser.

"The number of calories supplied within the condens- Patented Feb. 12, 1957 z ing chamber is such, that the sum of the calories supplied and of the heat furnished by the metallic vapors and given up by the condensation of these vapors has a constant value any given instant. i

In a preferred embodiment, the calories are supplied substantially along the center line of the condensing chamber, the temperature of the inside walls of the chamber on which the metal is condensed being maintained thereby at a temperature slightly higher than the melting point and less by at least 50 degrees (centigrade) than the dew point at the vacuum used.

By reason of this heat source placed on the inside of the condensing chamber, there is obtained a continuously decreasing temperature gradient from the center of the apparatus to the outside. The heat source is at a temperature above the dew point; in the case of magnesium, the active surface of the condenser is at 650 C. and the external surface has a temperature close to the ambient temperature.

A double control is insured on the inside and on the outside, by controlling the inside heat source and the external cooling.

Among the principal advantages obtained by proceeding in accordance with the invention, are the complete absence of parasitic condensations within the condensing chamber, and a remarkable thermal yield by reason of the absence of useless heat losses due to radiation and convection.

The heat emitted by the heater (reheater) is entirely transmitted to the condensing surface, the energy consumption is lower.

The heat and cold sources are independent and include the condensation isotherm, thus making possible a more flexible temperature control.

The invention further relates to an apparatus for continuously condensing metals which have been previously brought to the vapor state, thus enabling the above mentioned process to be carried out. Calories are supplied by an electrical resistance located along the center line of a cylinder-shaped condensing chamber, the walls of which comprise at least two coaxial metallic envelopes. Means are provided for varying the magnitude of the electrical resistance which is, for example, supplied with energy through a variable voltage transformer. The external surface of the envelope having the largest diameter is cooled by water or air. The metal, condensed to the liquid state, falls into a sealed container.

A first embodiment of the device, according to the invention, is shown in diagrammatic form in Figure 1. Figure 2 illustrates diagrammatically another embodiment. In the drawings, the same numerals designate the same parts. v

Referring to Figure l, the vapors from the furnace are passed to the condensing chamber by means of duct 1. The condensing chamber is constituted of a vertical iron cylinder 2 inside which is coaxially placed another smaller cylinder 3, likewise of iron, and heated by the adjustable electrical resistor 4. The portion of the condensing chamber which acts as the condenser proper is surrounded with a third cylinder 5, cooled externally either by the ambient air or by a water spray, as shown at 6. The cooling efitect can be varied by any suitable means, which, in the interest of simplicity, are not illustrated on the drawings.

The space 7 contains air which is trapped therein without communication with the outside; heat escapes therefrom by convection and radiation.

Condensed meta. runs into crucible or receiver 8 maintained, for example, in the case of magnesium, at a temperature slightly above 650 C. (by means of the resistor 9). A vacuum of the requisite degree is maintained in the furnace and in the condensing chamber by 3 asuitable apparatus (not shown) connected to the chamber by the connection 10.

The temperature of the condensing wall is controlled by means of pyro net-er '12, so as to be, for example, in.

the case of magnesium, slightly above 650 C. For this purpose, two controls are available: heating by means of resistor 4, which can be increased, decrease, or even eliminatedaltogether, and cooling of the external cylinder 5, as by the spray 6.

Electric current is supplied to the resistor 4 through the variable transformer '11 which, in turn, controlled by the pyrometer 12 through the temperature regulator 13 and a control 14, which adjusts the transformer voltage.

The condensing surface and its cooling devices are so calculated, that it is capable of condensing to the liquid state the maximum output of metal vapor that can be evolved by the producing furnace at any moment of the production cycle. When this maximum output flows into the condenser, the heat evolved by the condensation of the metal is sufiicient to keep the pyrometer 12 at the desired temperature, so that the resistor 4 can be completely cut out and the cooling means 6 then works with maximum effect.

On the contrary, when but a slight flow of metallic vapor arrives into the condenser, the resistor 4 supplies maximum heat, and external cooling by the means 6 is eliminated.

The invention is not limited to the devices shown in the drawing .described above: for instance, the heating device 4 may comprise two resistors, one for the vapor circulation zone 15, and the other-provided with a different regulating schemefor the condensing zone.

In another embodiment of the present invention, the space '7 is fitted with a stationary semi-heat-conducting material, e. g. iron filings, which act as a heat accumulator, and from which is eliminated by conduction to the outside, the calories (sensible'heat) given up by the vapors of the metal, e. g. magnesium and the calories released by their condensation. A fluid or liquid can also be circulated through the space 7 in a closed circuit with one or several tanks in which said fluid or liquid ay be either heated .or cooled.

:Figure 2 shows a preferred embodiment of the invention, in which the walls of the condensing chamber are formed by three coaxial cylindrical metallic envelopes 2E, 22 and 23 respectively, of increasing diameters; the envelope 21 having the smallest diameter is open at its lower end, so that the internal and external surfaces of this envelope, together with the inside surface of the envelope 22 having the mean diameter, are in contact with the metallic vapors which are condensed on these surfaces to the liquid state. The space between envelopes 22 and 23 contains air which is cut off from communication with the outside. The outlet 1%? to the vacuum pump is located at the top of the envelope 22. Pyrometer 12'measures the temperature of this envelope 22. in the case of magnesium, this temperature is maintained slightly higher than 650 C. by the same means as .in the system illustrated in Figure 1.

The apparatus of the embodiment illustrated in Figure 2 has several advantages: for the same floor space, the condensing surface is greater; moreover, the vapors given off by the liquid metal held in crucible '8 pass through the annular space between envelopes 21 and 22 and are there condensed so that there is no possibility of their escaping through the connection 10.

Example I i The condenser is of the type having three metallic coaxial cylinders as shown in Figure 2; every cylinder is three meters high; the diameter of the external cylinder 23, which is the only one that is air cooled, is 1.60 m.; that of the intermediate cylinder 22 is 1.20 m., and that of cylinder 21 is 1,06 m.; the tube containing'the resistor 4- has a diameter of 0.90 m.

The condenser condenses on an average 61.5 kg. of liquid magnesium per hour. 7

The output of resistor 4 is so controlled by the pyromcrer 12 that the temperature at the internal surface of the cylinder 22 is maintained at 650-660" C.

In the cylinder 21, the temperature does not exceed 690-700 C. under a vacuum from 10 to 15 mm. Hg. (dewpoint 740760 C.)

For an operating time of 40% hours, the resistor 4, operating at a variable output, had a total consumption of .7410 kwh. and there were obtained 2506 kg. of magnesium in liquid state. The condenser liquid output reached 90%; V 7

Example 11' With a condenser of the same size, but with only two coaxial cylinders (as in Figure 1), an average quantity of kgs. of liquid magnesium is condensed per hour.

The temperature at the internal face of the condensing chamber is maintained'at 650.66 0 C. (by the regulator 13, 14, operated by pyrometer 12).

The condenser output of liquid reaches The process and apparatus described may be used with all condensable metals, and the following metals are given by way of example and not by way of limitation: magnesium, zinc, cadmium, aluminum, tin, lead, calcium, barium, and the alkali metals.

As will be seen from the foregoing description, applicants have provided an improved method and apparatus for advantageously inhibiting the condensation of metal lic vapors to the solid state, despite wide variations in the rate of how of vapors to the condensing chamber.

By the provision of a controllable, independent heatsource, applicants are enabled to supplement automatically, at any given instant, the total heat given up by the vaporsi. e., the sensible heat and the latent heat of condensation-so as to maintain thetemperature of the condensing surface above the melting point of the metal at the prevailing pressure. In' this manner, the heat supplied to thecondensing chamber from all sources maintained substantially constant and at least equal to the heat radiated away from the chamber and/or removed by the cooling means, whereby the temperature of the condensing surface can be maintained above a predetermined desired value.

I claim:

1. Apparatus tor condensing -metallic v pors to the liquid state comprising: a cylindrical chamber; means for introducing metallic vapors into said chamber; means for oling a Wall of sa d c m e to P v d a conden ing r c a d v p r m ns for supply ng hea o s id chamber to control the temperature of said condensin surface, said means comprising a source of heat located substantially along the longitudinal axis of said chamber;

means for measuring the temperature at the condensing surface; regulating means, automatically .contliolled by said temperature measuring means ,for varying the heat upp t t c b an a connection to means for maintaining the condensing chamber under vacuum.

2. Metallurgical apparatus, including means ,for :con- (lensing the metallicvapors to theliquid state, comprising in combination: means for generating metallic :vapors; a cylindrical chamber; means for introducing the metallic vapors into said chamber; means for cooling the cylindn'cal wall of said chamber-to .provide va condensing surf e .tc sai vapors; means ifOI' -.supplying heat to said chamber to cqntml :the temperature of said condensing r a e. aid mea ompr sing a source of heat. eind pendent of said vapor generating means, located substantially along the longitudinal axis of said chamber and substantially coextensive with said condensing surface, and a connection to means for maintaining the condensing chamber under vacuum.

3. An apparatus according to claim 2, wherein the heat source comprises a resistance located in a closed cylinder concentric with said chamber, and wherein an additional cylindrical condensing surface concentric with the chamber, is located within the chamber between the said first condensing surface and the closed cylinder, said additional cylindrical condensing surface being substantially coextensive with the said first condensing surface.

4. Apparatus according to claim 2, comprising a sealed receiver for the liquid metal condensed in the chamber, and means for controlling the temperature of the metal in the receiver.

5. Apparatus according to claim 2, comprising means for controlling the cooling of said condensing surface and separate means for controlling the amount of heat supplied to said chamber.

6. Apparatus according to claim 2, wherein the wall is 6 formed of two spaced metallic shells forming an air jacket sealed to the outside, and wherein the cooling is applied to the outer member while the inner member constitutes the condensing surface for the vapors.

7. Apparatus according to claim 2, wherein the wall consists of two metallic shells forming a space therebetween, and said space is filled with a semi-heat-conducting material.

References Cited in the file of this patent UNITED STATES PATENTS 2,018,266 Kemmer Oct. 22, 1935 2,239,371 Osborn Apr. 22, 1941 2,251,906 Hanawalt Aug. 12, 1941 2,268,779 Seifert Jan. 6, 1942 2,477,420 Rhoades July 26, 1949 2,559,419 Fouquest July 3, 1951 2,615,706 Davey Oct. 28, 1952 FOREIGN PATENTS 700,174 Great Britain Nov. 25, 1953

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