US2370812A - Apparatus for producing magnesium by thermal reduction - Google Patents

Description

March 6, 1945. L. M. PIDGEON 3 2 APPARATUS FOR, PRODUCING MAGNESI M BYUTHERMAL REDUCTION Filed March 5, i942 UNITED s'rA'rss "garem orrics I 2,370,312

APPARATUS FOR PRODUCING MAGNESIUM BY THERMAL REDUCTION Application March 5, 19%2, Serial No. 433,452 In Canada February 21, 1942 Claims. (Cl. 266-159) This invention relates to the thermaiproduc tion of substantially pure magnesium by ferrosilicon reduction under reduced pressure, and

more particularly to apparatus therefor.

While the literature discloses much relating to the thermal production of magnesium with reducing agents, commercial use ofthe method has been surrounded by dangerous hazards as well as economic problems. Indeed the commercial production of the pure metal by direct ferro= silicon reduction has been considered impracticable. if not impossible. A 'Applicant has produced ure magnesium in coherent dense form by direct thermal ferrosilicon reduction of calcined magnesium containing material. The reducing vessels or.retorts are allowed to remain in a heating furnace maintained at substantially constant temperature and the retorts are charged and discharged in air,

without the hazard of fire or explosions. Prior applications 417,810, now Patent No. 2,330,142,

September 21, 1942, and 427,004, relate to this 3 process and apparatus therefor. The object of the present invention is to provide further improvements, which facilitate discharge of the spent residue with economy of time, which permit increased production capacity of each retort, which conserve heat, and others which will appear from thefollowing description with reference to the accompanying drawing in which Figure. 1 is a transverse section of. a furnace showing a plurality of retorts, one of which is in longitudinal section the furnace being shown as broken away. Y Y

Figure 2 is a transverse section 01'- a furnace showing a retort in longitudinal elevation- In the drawing I represents a heating furnace having located therein the reducing portion 2- of any desired number of retorts 3. In Figure 1 ,the retorts are vertically disposed within the furnace, while in Figure 2 they are disposed at wall of the condenser shell where the magnesium A plurality of these hot baflles extending into the condenser may be used to 1 tive.

an angle preferably just greater than the angle of repose ofthe residue of the charge for convenience in discharge of the spent residue. Each end of the retort projects beyond the furnace. In the upper or condensing end 4 of the retort is located a removable condenser 5, having an internal diameter of not less than that of the reducing zoneof the retotth This end of the retort is closed by a. removable head 6 and has a fractioneting condenser I. As shown the latter comprises a seriesof spaced metal discs, S arranged within and adjacent the outer end of the removable condensento provide a relatively long The gasket 22 for sealing the connection bepath of travel for vapours through zones of progressively lower tenipera'ture. While as illustrated five such discs are shown, any desired number may be used to provide optimum temperature conditions for fractionating the metal vapours and independently condensing them in solid form. The discs are shown as carried by the plate 6 which closes the removable condenser for convenience in their removal. It will be apparent however that they could be held in place and removed independently of the closure plate.

The plate 8 may be provided with lugs 8a for convenience in removal and a spring 25 holds it in place. The discs are shown mounted on tapered rods fizz for ease in assembly. The innermost disc 9 is out of thermal contact with the condenser wall and is preferably carried by the adjacent disc by means of thin rods 91) so as to completely-avoid undue cooling of this disc, which in operation is maintained relatively hot by impingement ofthe metal vapours. This hot disc acts as a baflle to direct the hot vapours to the deposit forms.

regulate the location of the deposit.

10 represents means for providing a. reduced I retort. Four discs as shown have proven eifec- The purpose of the shield is to prevent as far as possible thetransference of unnecessary heat to the condenser.

The lower end of the retort is provided with a removable closure l3 secured by clamps H or the like to a flange I! on the retort. A' plug l6 seals the heated reducing zone of the retort.

' plug is preferably tapered to rest against a com- :plementary taper or shoulder on the retort wall.

' The sealing plug is removable upon opening this end of the retort. Water circulation or like cooltween the closure and retort is preferably carried by the flange I! and it is further protected by the-- V electrically as by the resistors 25. The retort is disposed uiiiformly' with respect to the heat re.-

diating walls of the furnace in order to insure maximum uniformity in heating the charge within the retort. It will be observed that the heated portion of the retort in which the reducing action takes place under reduced pressure ismaintained in a substantially constant and uniform temperature in the furnace. Thisavoids temperature shock to the metal of the retorts. This is an important consideration since even a minute crack in a retort renders it useless. The heat resisting alloy steel of whichthe retorts are composed is costly and maintenance oflong life of the retorts is a large factor in the unit cost of the magnesium produced. Any desired number of retorts may be used in a furnace. The furnace pro vides a static heat reservoir, preferably in an oxidizing atmosphere free from sulphur or other compounds which react with the retort metal.

The vertical or angular disposition of the retorts facilitates discharge by gravity of the residue when the bottom closure is removed. This arrangement with its bottom discharge for the residue permits the use of retorts having within the furnace :3. long reducing portion, which will handle a larger charge than when the residue is discharged through the condenser end. This afl'ords increased production of metal per operating cycle and facilitates discharge of the residue.

In operation with the lower end of the retort closed a portion of finely divided unreactive material 21', suchas the residue of a treated charge, is placed over the plug it to substantially seal the closure and avoid passage at this point of magnesium vapour from the reducing zone of the retort. This provides a hot vapour tight closure for the lower end of the reducing portion of the retort. In operation this seal remains at a temperature above the condensing point of the magnesium vapour. Being insulated loss of heat to the water cooled atmospheric pressure chamber below the seal is avoided. The use of a gas, such as hydrogen, is unnecessary in directing the flow of vapour to the condenser. A charge of magnesium containing material is, placed in the reducing zone of the retorti The preferred charge is crystalline dolomite or crystalline brucitic limestone which has been calcined and mixed with a reducing agent, preferably ferrosilicon. The briquetted material is preheated in air and the degassed charge is fed hot into the retort. The removable condenser shell is inserted, the top 016- sure put in place, and the retort is evacuated to provide therein a pressure preferably less than 0.5

magnesium metal deposit is then removed from the retort. The bottom closure l3 and the plug lfa'fremoved for the gravity discharge of the residue. To avoid unnecessary loss of heat from the hot reducing portion of the retort one end of the retort should be closed while the other is bein discharged.

Both ends of the retort being without the-high temperature of the furnace are not adversely 2.1

fected by the mechanical manipulation of the closures and condenser upon charging and discharging the retort. Sodium and like vapours being condensed and removed independently of the magnesium the danger-of igniting the dense mag nesium deposit upon-contact with air is eliminated. R\

'I claim: a

-1. Apparatus for producing magnesium by thermal reduction comprising a heating furnace,

a metallic retort having a central reducing portion within the furnace with a condenser portion at one end without the furnace and a residue disa charge portion at the other end without the furnace, means within the residue discharge portion sealing it from said central reducing portion of the retort and fractionating condenser means within the condenser portion to cause magnesium vapour to condense at a point removed from the outer end of the condenser portion of the retort.

2. Apparatus as defined in claim 1 having a re movable closure for the outer end of the residue discharge portion and wherein said sealing means is supported in place by said closure.

3. Apparatus comprising a retort for the production of magnesium by thermal reduction comprising a metallic retort having a central reducing portion, a magnesiumdischarge portion at one end and a residue discharge portion at the other end, a heat reservoir surrounding said central reducing portion, removable sealing means residue discharge portion, fractionating condenser means within the magnesium discharge portion to cause magnesium vapour to eondense at a point'removed from the outer end of said discharge portion, and a removable condenser within the magnesium discharge portion.

4. Apparatus for producing metallic magnesium by thermal reduction of magnesium ore with ferrosilicon comprising a plurality of metallic retorts having a central reducing portion, a metal discharge portion at the upper end and a residue discharge portion at the lower end, a heating furnaceenclosing the central reducing portion of mm. of mercury during the initial stage of heating denser shell as indicated at 28. The vacuum producing means is shut off and-the top closure of the retort is removed for discharge at atmospheric pressure. The fractionating condenser I in which sodium and like vapours have been condensed is removed with the plate 8 or separately as indicated. The condenser shell with the dense the retorts, a vapour seal closing the lower end of the reducing portion, means within the metal discharge portion to cause magnesium vapour to condense at a point removed from the upper exposed end of the retort, and a series of spaced discs constituting a heat baflle in the upper end of the reducing portion of each retort.

5. Apparatus for producing coherent magnesium by thermal reduction comprising a plurality of metallic retorts, a heating furnace enclosing the central portion of the retorts with the end portions thereof outside the furnace, a vapour seal for the residue discharge end of the central portion removable through one end of each retort, and a plurality of spaced discs constituting a frac-. tionating condenser removable through the other end of each retort.

LLOYD MONTGOMERY PIDGEON.

.between the central reducing portion and the

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