SK283044B6 - Retort furnace for the production of magnesium - Google Patents

Abstract

Retort furnace for production of magnesium The retort furnace is for production of magnesium by reduction of a charge (12) of oxidic magnesium, particularly dolomite lime, using a reduction agent, specifically ferrosilicon, at temperatures at least equal to 1000 degrees C in partial vacuum. The furnace has a horizontal chamber furnace with at least one retort chamber (3) extending over the length of the furnace. The retort chamber has walls made of a refractory material, and has a vacuum-tight sheet metal inner lining. There is a heating chamber on each side of the retort chamber, and condensers (9) to condense the magnesium vapour and to remove the condensed magnesium. These condensers can be joined to the charging openings (7) with a vacuum tight seal.

Description

Technical field

The invention relates to a retort furnace for the production of magnesium by reducing the charge of oxidic magnesium, in particular dolomitic lime, with a reducing agent, in particular ferro-silicon, at temperatures of at least 1000 ° C and under vacuum. The invention further relates to the use of a horizontal chamber coke oven.

BACKGROUND OF THE INVENTION

The fully prevailing share of world magnesium production is produced by an electrolytic process from magnesium chloride. This method is very costly, since a large amount of energy is required and there is a problem of by-products and waste products. Magnesium chloride must therefore be expensive to chemically process. This results in a relatively high cost of magnesium, although it is present in sufficient quantities in the magnesium compounds.

It is also known to obtain magnesium by thermal reduction of magnesium oxide, which is widely available in the form of dolomitic lime (CaO.MgO). To this end, the dolomitic lime is mixed with a reducing agent, which may consist of an inexpensive ferrosilicon, preferably in a stoichiometric ratio of 2: 1 and placed in a refractory steel retort. The steel retort is externally heated to a reaction heat of 1200 ° C and vacuumed at 10 mbar. At the cold end of the retort, magnesium vapor condenses to form metallic magnesium. This method, called. The Pidgeon method does not allow high yields because it is limited by the size of the retort due to the heat resistance of the steel retort at high temperatures. The industrial tube retorts are 3 m long and have an internal diameter of 27.5 m. Economical use at these small production capacities is conceivable only for very pure special magnesium.

In a similar way, so-called. The Bolzano process, a silicothermal reaction is carried out with the same starting materials in a reactor which is internally heated by a stream. This reactor consists of a steel tank which is lined in the area of heating from the inside with a refractory material. The dome top is cooled so that magnesium vapor condenses on the dome walls and magnesium deposits on the walls. The dome is removable to obtain magnesium. This method is also uneconomical because the mechanization of charging and emptying the reactor is difficult. In addition, electrical heating is not economical as it does not allow the use of heated waste gases.

SUMMARY OF THE INVENTION

The problem of the prior art is that the production of magnesium is not environmentally friendly nor economical. As the use of magnesium as a light foundry metal, for example in the automotive industry, is increasing, there is a great need for improved magnesium recovery.

This problem is solved according to the invention by a retort furnace of the aforementioned type, which is formed as a horizontal chamber furnace with at least one retort chamber positioned in the longitudinal direction, having refractory walls and a vacuum sealing inner metal sheet lining. filler apertures with heating chambers positioned bilaterally along the retort chamber and with condensers for cooling the magnesium vapors and depositing condensed magnesium that are formed to a vacuum seal connection to the filler apertures.

Horizontal chamber furnaces which are heated externally are known for the production of coke. Retort furnace units are used, which can be up to 14 m long, 6 m high and 0.3 to 0.6 m wide. For example, each furnace element may comprise 30 t of coal. The retort furnace is fed through the filling openings on the upper side, while the coke to be produced is removed with the door open by means of unloading machines on the front sides of the furnace elements. Such coke plants have a high degree of mechanization as they have been developed for many decades.

The retort furnace of the present invention for the production of magnesium is similar to the design of the known coke oven, but is modified according to the invention to effect thermal reduction of magnesium oxide without altering the handling that has been proven in coke production. By means of the sheet metal lining, the retort chamber is made tight against the vacuum, so that the vacuum needed to produce magnesium can be created. In addition, condensed magnesium can be removed by means of vacuum-tight capacitors connected to the feed openings such that the capacitors can be replaced, for example. The metal used for the sheet metal lining is preferably austenitic steel or an alkaline nickel alloy that is stable at the temperatures required for the reduction reaction, which is between 1200 ° C and 1300 ° C, and also under vacuum conditions, while dropping the sheet metal lining the inner side of the wall, at high temperature and under vacuum conditions, can preferably be prevented by inserting briquettes. Dropping of the liner from the sheet can be prevented in the unfilled upper portion of the retort chamber by guiding the sheet liner inside the refractory material in this portion and preferably terminating with a cover fitting that closes the retort chamber on its upper side.

The retort furnace according to the invention allows the use of the Pidgeon process in a very economical form. The economy can be further increased by the use of existing but no longer required coke ovens which are additionally equipped with the sheet metal cladding according to the invention and which are provided in the filling openings or on the filling openings for aligning the capacitors.

In a preferred embodiment of the invention, the capacitors are connected to each other and to the vacuum source by means of a vacuum line. Vacuum of the retort chamber occurs via connecting flanges on capacitors connected to the filling holes.

Preferably, the capacitors are designed to be vacuum sealed to seal the filler orifices. Preferably, they substantially extend the feed opening, wherein the magnesium precipitate forms on the capacitor liner that is removable.

The walls of the capacitors are preferably water cooled.

The sheet metal lining may consist of austenitic steel as well as a basic nickel alloy and is stable under the action of temperature and vacuum. In this case, it may be expedient to anchor the sheet metal lining to the walls of the rotor chamber of refractory material.

The refractory material, preferably made of silicate masonry, has practically no thermal expansion in the temperature range between 600 ° C and the reaction temperature. Since this does not apply to sheet metal linings, it is preferable to provide the sheet metal linings with longitudinal or transverse bulges to compensate for thermal expansion.

The door of the retort chamber located at the front of the horizontal chamber furnace, as a rule, is vacuum-sealable, preferably by means of a paste-like, castable or spray-sealing sealing device. To prevent draining or dripping of the sealant, the door or door frame is provided with pocket-like segments to receive the sealant.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by the following examples, schematically shown in the drawings. In the drawings: FIG. 1 shows a longitudinal section through a retort furnace according to the invention, FIG. 2 shows a schematic view of a door on the front side with pocket segments for a sealant, FIG. 3 is a vertical cross-sectional view of a capacitor mounted on a feed opening, FIG. 4 is a cross-sectional view of the retort chamber and the adjacent heating chamber of the retort furnace of FIG. 1, FIG. 5 detail A of FIG. 4, which shows the construction of a refractory material with a metal sheet lining; and FIG. 6 shows a detail B from vertical FIG. 5, showing a tension anchor bolt.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 shows a horizontal chamber furnace 1 having a bottom structure 2 and a retort chamber 3 formed along its entire length. The retort chamber 3 is closed on both ends by doors 4, 5. Under the doors 4, 5 there are placed outside the horizontal chamber furnaces 1 of the substructure. 6, on which a skidder (not shown) or a conveyor device of the skidder is located.

The retort chamber 3 has, in the illustrated embodiment, filling holes 7 which are formed between the cover pieces 8.

Capacitors 9 are mounted on the filling holes 7, which are connected to each other and to the vacuum source 11 by means of a vacuum line 10.

FIG. 1, it can be seen that the retort chamber 3 is filled with briquettes 12, which are made of a mixture of dolomitic lime (CaO.MgO) and ferro-silicon, with the upper part of the retort chamber 3 not being filled.

Fig. 2 shows a plan view of the door 4, 5 on the front side of the retort chamber 3. In contrast to the corresponding door on the coke oven, the door 4, 5 on the chamber furnace 1 according to the invention must be vacuum-sealed so that a seal must be formed. This is achieved, for example, by spraying, pouring or preferably spraying the sealing means 14 into the sealing joint, the sealing means 14 having to be applied in excess in the paste-like or liquid form, thereby sealing the sealing means 14 into the sealing chamber under negative pressure. In the retort chamber 3 or on the door 4, 5, the sealing effect is hardened. Since the sealing means 14 in liquid form can leak or drip in the region of the door 4, 5, the doors 4, 5 are provided with pocket segments 13 by means of which the leaking sealing means 14 can be trapped.

Fig. 3 shows an enlarged detail A of FIG. 1 of a construction of an exemplary embodiment of a capacitor 9 which is provided in a housing 15 formed on the filling opening 7 and is sealed by a seal 16. The housing 15 is formed by a chamfer adapted to the shape of the housing of the capacitor 9. The capacitor 9 consists essentially of a cylindrical wall 17 continuing essentially from the filler opening 7, which is closed at its free end by a cover 18. The cover 18 is locked in the closed position, which is not shown, and has an eyelet 19 for lifting the cover 18 or the entire condenser 9 with closed, locked cover 18. there is an insert 20 having the shape of an inverted cup on which magnesium is deposited in the form of steam.

The inner space of the cylindrical wall 17 is connected to the vacuum connection flange 22 by means of a guide 21. A vacuum guide 10, as shown in FIG. First

The cylindrical wall 17 is surrounded by an outer cylindrical wall 23 which is provided with an inlet throat 24 and an outlet throat 25 for cooling water, by means of which the cylindrical wall 17 and thus the liner 20 are cooled to a maximum of 100 ° C.

Fig. 4 shows a heating system for the retort chamber 3, which is made in an embodiment known for coke ovens. The walls of the retort chamber 3 are made of refractory material 26 and separate the retort chamber 3 from both sides of the adjacent heating chambers 27. Combustible gas is supplied to the heating chambers 27 and preheated air to the recuperator at several locations along the length of the heating chambers 27. are equidistant from each other. The flue gas continues through the upper exhaust opening 28, which is formed by the refractory rings 29, out of the chamber furnace 1.

The retort chamber 3 is provided on the inside of the refractory material wall 26 and at the bottom of the retort chamber 3 with a metal sheet lining 30. The metal sheet lining 30 is supported flat on the refractory material walls 26. The deposition on the refractory material walls 26 is supported by filling the retort chamber 3 with briquettes 12.

In the upper region of the retort chamber 3, which is not filled with briquettes 12, the metal sheet lining 30 is progressively expanded outwardly, and in the upper part 31 is guided inside the refractory material 26 to avoid dropping of the metal sheet lining 30 in the area lining 30 of briquette metal sheet 12 at an outward pressure.

The outlet openings 28 are guided inside the fireclay 32 which covers the chamber furnace 1 outside the condensers 9.

Fig. 5 is an enlarged view of detail A of FIG. 1 of a wall structure of refractory material 26, preferably silicate, with a lining 30 of metal sheet. The refractory material walls 26 are assembled from the refractory fitment 33. The metal sheet lining 30 is prestressed by tension by means of tension anchor bolts 34 against the refractory wall 26 so that the metal sheet lining 30 is secured to the refractory wall 26 also when a vacuum and a high temperature are set inside the retort chamber 3.

Since the wall of refractory material 26, when it consists of a silicate, has no thermal expansion between 600 ° C and 1200 ° C and the metal sheet lining 30, on the other hand, expands considerably when hot, the metal sheet lining 30 has bulges 35, which can compensate, by increasing or decreasing, the thermal expansion of the metal sheet lining 30.

Fig. 6 shows a detail in FIG. 5, on which a metal threaded pin 36 is welded to the metal sheet lining 30 into which the thread of the tension anchor bolt 34 is screwed, so that by screwing the tension anchor bolt 34 the metal sheet lining 30 is tightened against the mating fitting 33 wall of refractory material.

The drawings show that the retort furnace according to the invention is modified with respect to the current coke ovens by means of a metal sheet lining 30 and by placing the capacitors 9 on the filling holes 7.

The capacitor 9 can be completely lifted after the cycle has been completed to obtain the separated magnesium. However, it is also possible to detach only the insert 20 after opening the cover 18 and to re-insert the retort chamber 3 after the insert 20 has been removed by opening the cover 18 of the capacitor 9. In this case, the casing of the capacitor 9 can be more or less firmly connected to the lining of the filling opening 7.

Claims (12)

PATENT CLAIMS A retort furnace for the production of magnesium by reducing a charge of oxidic magnesium, in particular dolomitic lime, with a reducing agent, in particular ferro-silicon, at temperatures of at least 1000 ° C and under vacuum, characterized in that it has a horizontal chamber furnace with at least one retort a chamber (3) formed in the longitudinal direction, which is provided with walls of refractory material (26) and an inner vacuum-sealed liner (30) of sheet metal and likewise upward filling openings (7), with heating sockets (3) chambers (27) and condensers (9) for cooling the magnesium vapors and for sedimenting the condensed magnesium, which are vacuum tightly connected to the feed openings (7). Retort furnace according to claim 1, characterized in that the capacitors (9) are connected to each other and to the vacuum source (11) by means of a vacuum conduit (10). Retort furnace according to claim 1 or 2, characterized in that the capacitors (9) are vacuum sealed on the seals (16) of the filling openings (7). Retort furnace according to one of claims 1 to 3, characterized in that the sheet metal lining (30) is made of austenitic steel. Retort furnace according to one of claims 1 to 3, characterized in that the sheet metal lining (30) is made of a basic nickel alloy. Retort furnace according to one of Claims 1 to 5, characterized in that the sheet metal lining (30) is anchored to the walls of the retort chamber (3) made of refractory material (26) with prestressing. Retort furnace according to one of Claims 1 to 6, characterized in that the sheet metal lining (30) is provided with longitudinal and / or transverse bulges (35) to compensate for thermal expansion. Retort furnace according to one of claims 1 to 7, characterized in that the vacuum-sealed sheet metal lining (30) is located in the filling area of the retort chamber (3) on the inner side of the wall formed of the refractory material (26). in the upper part (31) of the retorotvei of the chamber (3) guided inside the refractory material (26). Retort furnace according to one of Claims 1 to 8, characterized in that the retort chamber (3) is closed on its upper side by a cover fitting (8), wherein the sheet metal lining (30) terminates above the cover fitting (8). . Retort furnace according to one of Claims 1 to 9, characterized in that a door (4, 5) is disposed on the front side and is closed in a vacuum-tight manner by means of a paste-like, casting or spray-on sealing means (14). Retort furnace according to claim 10, characterized in that the door (4, 5) or door frames (4, 5) are provided with pocket-like segments (13) for catching a leaking or dripping sealant (14). Use of a horizontal chamber coke oven as a retort furnace for the production of magnesium according to claims 1 to 11 after lining the retort chamber (3) with a vacuum-sealed sheet metal lining (30) and placing the capacitors (9) on the filling openings (7).