US3033549A - Water cooled retort cover - Google Patents

Description

May 8, 1962 w. J. ASH ETAL WATER COOLED RETORT COVER Filed Aug. 12, 1960 INVENTORS WILLIAM J. ASH

E POZZI JOHN BY United States Patent 3,033,549 WATER COOLED RETORT COVER William J. Ash, Salisbury and John F. Pozzi, North Canaan, Conn., assignors, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Filed Aug. 12, 1960, Ser. No. 49,396 2 Claims. (Cl. 266-19) This invention relates to improved apparatus for the recovery of volatizable metals such as magnesium in substantially pure form wherein the metal to be recovered is first vaporized and then condensed. In particular, the invention pertains to a new and improved retort cover which provides a condensing surface for the vaporized metal and means for maintaining the said surface within a desired temperature range.

In the production of magnesium the raw material from which the metal is to be produced is placed in the hot end of a tubular steel retort and subjected to a high temperature of about 2l50-2200 F. and a vacuum of about 100 microns. This end of the retort is located within a furnace in order to maintain the necessary high temperature. The other or cold end of the retort is located outside the furnace and has a removable head or closure which is furnished with a gasket to make the retort vacuum tight. This gasket must be protected from excessive heat which would damage it and destroy the seal thereby permitting inleakage of air and loss of vacuum. On the other hand, it is known that if magnesium is condensed at too low a temperature the deposit is finely divided and pyrophoric. Therefore the temperature of the condensing surface for the metal must be maintained sufiiciently high to cause the magnesium to be deposited 'in massive form, in which condition it may be safely handled in air even 'at elevated temperatures. It is accordingly an object of this invention to provide a new and improved retort cover which is so constructed and arranged as to provide a high temperature condensing surface for the magnesium vapors while simultaneously protecting the retort gasket from damage due to excessive temperatures.

Another object is to provide a retort cover having its sealing surface isolated fromthe region of hot metal by closely disposed water cooled surfaces which act as cold traps in preventing th passage of hot water vapors.

The invention may be better understood by reference to the accompanying drawings wherein:

FIG. 1 is a cross section showing the general arrangement of a retort assembly when employing the invention; and

FIG. 2 is a cross sectional view taken along line Il -II of FIG. 1.

As shown in FIG. 1, the assembly consists of a tubular, stainless steel retort mounted in a furnace wall 11 of a refractory material, such as brick, and closed by a cast stainless steel cap 12 at its inner end. The material to be heated is indicated schematically at 13. In the practice of this invention it is important that this starting material be substantially free of metal compounds having higher vapor pressures than those of the magnesium being produced. Specifically, impurities in the raw material that generate sodium or potassium must be avoided, if the final condensed metal deposit is to be of high quality magnesium.

At its outer end the retort is provided with a slightly enlarged section 14 which is joined to section 10 by an intermediate section 15. At the point where the retort assembly emerges from the refractory furnace wall 11, a stainless steel wrap 16 encases section 15.

An annular flange 17 is welded to the outer end of secthen remains substantially uniform Patented May 8, 1962 tion 14, which outer end is surrounded by a water jacket 18 having connections 19 and 20.

A perforated plate 21 separates the hot and cold ends of the retort and serves to reduce heat losses.

In order to evacuate th retort, a conduit 22 communicates with the interior of the retort and may be attached to a suitable vacuum pumping means (not shown).

A condensing sleeve 23 is located within the section 14 of the cool end of the retort to receive the condensed deposit'of metal indicated schematically by 24. The elements heretofore described are old in the art and form no part of the present invention.

The novel and improved portion of the assembly illustrated in FIG. 1 consists of the retort cover. This comprises a circular steel cover plate 25 provided with a pair of handles 26, one of which is shown in the drawing, FIG. 1. A pair of brackets 27 engage the flange 17 and position the cover over the open end of the retort. An annular shoulder 28 on the cover plate positions a neoprene gasket 29 which engages a boss 30 on the flange 17 to seal the cover to the retort.

A stainless steel cylindrical section 31 slightly smaller in diameter than the condensing sleeve 23, is welded at one end to the cover plate at 32. The opposite end of section 31 is closed by a mild steel disc 33 which is welded thereto as indicated at 34. The Zone or chamber so formed is divided by a mild steel partition 35 into two approximately equal compartments 36 and 37. At the extreme upper portion of the partition 35 a hole or opening 38 is provided to permit introduction of a granular mineral insulating material into the compartment 36 to the level indicated by 39. The opening permits escape of any steam generated in the insulating material during operation of the retort.

A water connection 40 permits water to be introduced or withdrawn from compartment 37. The water level 41 in this compartment is determined by the position of a further opening 42 in the cover plate 25 at a distance below the opening 38 in partition 35.

In operation, the retort is loaded with a magnesium containing material in the form of briquettes as schematically indicated at 13, the briquettes being substantially free of metal compounds such as sodium and potassium having higher vapor pressures than magnesium. The perforated plate 21 is placed in position. After the condenser sleeve is inserted and the head is put on, the retort is evacuated through conduit 22. This is accomplished in two steps, first a roughing vacuum down to about 1500 microns pressure, followed by a fine vacuum down to operating pressure of about microns. The application of the vacuum holds the cover sealed against the flange 17.

Heat is applied to the end of the retort containing the charge, and water is introduced into the compartment 37 either through the connection 40 or through the opening 42. As heat continues to be applied to the retort, the temperature of the steel disc 33 rises rapidly, due to both outgassing and radiation to approximately 500 F., at which temperature a state of equilibrium is reached with no substantial change taking place in the temperature of the disc until evolution of magnesium vapor commences. At this time another sharp increase in the temperature of the disc takes place. In the case of magnesium, the temperature of the plate may reach 900 F. to approximately the melting point of magnesium, 1204 F. The temperature for a period of ap proximately two hours, after which the temperature of the disc slowly declines throughout the balance of the cycle, eventually reaching 600 F. to 800 F. This slow decrease in temperature is probably a result of the increasing thickness of the metal deposit, causing the actual condensation zone to move progressively away from the disc so that an increasing amount of heat is transmitted to the Water jacket 18; Simultaneously with the deposit of magnesium on the disc 33, deposition occurs on the inner surface of the sleeve 23.

Throughout the condensation cycle, water is maintained in the compartment 37 to cool the cover plate 25'. The Water in this compartment, in combination with the Water in the jacket 18, protect the gasket 29 from overheating. Use of the construction of this invention has fully and clearly established the fact that in both experimental and commercial production operations the life of the gasket has been materially extended.

Upon completion of the condensation cycle, the vacuum connection is closed and air is introduced into the retort. After the vacuum in the rotor has ben broken, the cover is given a sharp blow with a heavy bar, thereby separating the cover from the magnesium deposit. The cover is then lifted from the retort, the sleeve is next removed and the magnesium deposit is recovered therefrom.

In practice it has been found that the surface of the disc 33 should preferably be covered with an oxide coating before its initial use. This coating may be applied by washing the cover with a lime solution. After such treatment, the disc 33 will break clean of the deposited magnesium upon completion of the cycle. The same clean break will occur with covers that have once been used, as the conditions prevailing in the process will cause an iron oxide coating to form on the condensing surface 33. Covers not having an oxide coating on the condensing surface may adhere to the deposited magnesium and are therefore to be avoided.

It will be readily seen that the axial location of the plate 35 may be modified to effect changes in the ultimate temperature reached by the plate 33. For example, a decrease in the thickness of the volume 36 accompanied by an increase in the thicknes of the volume 37, thereby increasing the ratio of the water cooled zone to the insulated zone would permit a lower temperature to be reached in 33. Conversely, moving the plate 35 tothe right in FIG. 1 will increase the ratio of insulation to water and result in an increased maximum operating temperature on the plate 33. These variations in the configuration are necessary to adjust the temperature of the plate 33 to a satisfactory level for the rate of evolution of the metal being condensed. For example, in the production of magnesium in a retort of approximately in inside diameter and 10'6" overall length, it has been found that the outside diameter of the cylinder 31 should be approximately 9%", that the axial length of the space 36 should be approximately 2 that the axial length of the space 37 should be approximately 2%". In this example, the plate 33 is A" thick, the plate 35, thick and the plate 25, /2' thick.

In the practice of this invention, any suitable insulating material, even air, may be used in compartment 36, the kind and amount of such insulation being regulated as needed to provide a condensing surface at 33 at the highest possible temperature for the prevailing pressure in the retort. By reason of the high temperature of condensation, the magnesium deposit on the end Wall of the cover is extremely dense. In contrast, experiments in which the condensing surface was directly Water cooled proved a failure as the magnesium condensed too rapidly and produced a finely divided pyrophoric rather than a dense deposit.

We claim:

1. A retort cover comprising a cover plate, sealing, means on said plate for scaling the cover to a retort, a tubular corrosion. resistant metal section secured at one end to the cover plate, a condensing surface secured to the other end of the tubular section to define With said cover plate a zone, a partition in said Zone parallel to the cover plate and subdividing the zon into two compartments, one adjacent the condensing surface and one adjacent the cover plate respectively, insulating means in the compartment adjacent the condensing surface and means for introducing a coolant into the compartment adjacent the cover plate.

2. A retort cover comprising a cover plate, sealing means on said plate for sealing the cover to a retort, a tubular corrosion resistant metal section secured at one end to the cover plate, a condensing surface secured to and closing the other end of the tubular section and defining with the cover plate a zone, a partition in said zone. parallel to the condensing surface and to the cover plate and subdividing the zone into two approximately equal compartments, one adjacent the condensing surface and one adjacent the cover plate, means at the top of said partition defining an opening, means in the cover plate defining an opening below the opening in the partition, insulating means in the compartment adjacent the condensing surface, and means for introducing a coolant into the compartment adjacent the cover plate.

OTHER REFERENCES American Institute of Mining and Metallurgical Engineers, vol. 159, 1944 (pages 317-322, 368 and 369).

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