EP0889142B1 - Retort furnace for the production of magnesium - Google Patents

Abstract

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

The invention relates to a retort furnace for the production of Magnesium by reducing an oxidic feed Magnesium, especially in the form of dolomite lime, with the help of a Reducing agent, especially ferrosilicon, at temperatures ≥ 1,000 ° C and under a rough vacuum.

The vast majority of the world's magnesium production is produced from magnesium chloride in the electrolysis process. This process is very complex because of the high energy input is required and problems with by-products and waste products (especially chlorine and electrode sludge) occur. The magnesium chloride must also be chemically processed in a complex manner become. This results in a relatively high price for the magnesium, although there are rich deposits of magnesium compounds gives.

It is also known to magnesium by thermal reduction of magnesium oxide, which is in the form of dolomite lime (CaO MgO) is abundant to win. Dolomite limestone is included a reducing agent made from inexpensive ferrosilicon can exist, mixed, especially in a stoichiometric Ratio of 2: 1, and in a heat-resistant steel retort spent. The steel retort is external to a reaction temperature heated from about 1200 ° C and below 10 mbar evacuated. Magnesium vapor condenses on the cooled end of the retort, so that metallic magnesium is obtained. This Process (Pidgeon process) does not allow high yield, because because of the heat resistance of the steel retort at high temperatures the retort size is limited. Industrial tube retorts are 3 m long and have an inside diameter of 27.5 cm. With these retorts, 70 kg of magnesium per day be generated. An economic use is with these low production capacities, at best for high-purity special magnesium conceivable.

In a similar process (Bolzano process) with the same starting materials the silicothermic reaction in a reactor that can be heated internally with electricity. This reactor consists of a steel tank that is in the area the inside of the heater is lined with a refractory material is. The upper part of the steel reactor formed by a dome is cooled so that magnesium vapor on the walls of the dome condenses and magnesium attaches to the walls. The Dome is removable to extract the magnesium. This too The process is uneconomical because the feed is mechanized and emptying of the reactor is hardly possible. About that in addition, the electrical heating is not economical because it does not allow the use of heated exhaust gases.

The problem that arises from the prior art thus in that an environmentally friendly and economical manufacture of magnesium is not possible. Because magnesium as light and castable metal increasingly, for example in automobile construction, is used, there is a considerable need improved magnesium production.

According to the invention, the stated problem is solved with a retort furnace of the type mentioned, solved as a horizontal chamber furnace is formed with at least one over the longitudinal direction extending retort chamber with walls made of fireproof Material and an inner vacuum-tight sheet metal lining and is provided with filling openings at the top, along the retort chamber heating chambers arranged on both sides and with condensers for cooling magnesium vapor and picking up of condensed magnesium, which seals to the vacuum sealed Filling openings can be connected.

Horizontal chamber furnaces that are heated externally are used to produce coke known. Retort furnace units are used which can be up to 14 m long, 6 m high and 0.3 to 0.6 m wide. Each furnace element can hold 30 tons of coal, for example. The retort furnaces are loaded through filling openings at the top while using the coke produced Broaching machines with the doors open in the front of the furnace elements is applied. Such coking plants have a high degree of mechanization since it has been used for many decades have been further developed.

The retort furnace according to the invention for the production of magnesium Similar to the structure of the known coke oven, but is to be carried out the thermal reduction of magnesium oxide according to the invention have been modified without doing that in coke production to change proven handling. Through the sheet metal lining the retort chamber is vacuum-tight, so that the Vacuum formation required for magnesium reduction possible is. In addition, the condensed magnesium with the capacitors connected vacuum-tight to the filling openings remove, for example, the capacitors be replaced. The one used for the metal sheet lining Metal is preferably austenitic steel or a Nickel-based alloy, which is necessary for the reduction reaction Temperatures, in particular between 1200 ° and 1300 ° C, also withstands vacuum conditions, with a Drop in the sheet metal lining on the inside of the walls under the high temperature under vacuum conditions be expediently prevented by filled-in briquettes can. The sinking of the sheet metal lining can be done in the non-fillable This prevents the upper section of the retort chamber be that the sheet metal liner within this section of the refractory material and is preferably above is closed by ceiling stones that attach to the retort chamber complete their top.

The retort furnace according to the invention allows the use of Pidgeon's process in a very economical way. The Profitability can be increased by the fact that for the Magnesium production still existing but no longer needed Coke ovens can be used that are retrofitted with the invention Provide sheet metal lining and to accommodate the capacitors be changed in or at the filling openings.

In a preferred embodiment of the invention, the capacitors are with each other and with a vacuum line Vacuum source connected. The evacuation of the retort chamber takes place thus via connections to those connected to the filling openings Capacitors instead.

The capacitors are preferably vacuum-tight on seals the filler openings can be fitted. Conveniently they essentially extend the filler opening with a lid, with the precipitate of magnesium the capacitor is used, which is removable.

The walls of the capacitors are preferably water-cooled.

The sheet metal lining can be made of an austenitic steel as well as a nickel-based alloy and so under temperature and vacuum conditions. It can be appropriate, the sheet metal lining under tension anchor fireproof walls of the retort chamber.

The refractory walls preferably made of silica masonry have practically no temperature expansion in the temperature range between about 600 ° C and the reaction temperature. There this does not apply to the sheet metal linings, it is advantageous these with longitudinal and / or transverse beads to compensate for thermal expansion to provide.

The regularly provided for a horizontal chamber furnace front doors of the retort chamber are preferably with pasty, pourable or sprayable sealant vacuum-tight designed to be closable. To drain or drain the The doors or door frames can be used to prevent sealant Pocket segments may be provided for collecting the sealant.

Figur 1 -

einen Längsschnitt durch einen erfindungsgemäßen Retortenofen,

Figur 2 -

eine schematische Ansicht einer stirnseitigen Tür mit Taschensegmenten für Dichtungsmittel

Figur 3 -

einen Vertikalschnitt durch einen auf eine Einfüllöffnung aufgesetzten Kondensator,

Figur 4 -

einen Querschnitt durch eine Retortenkammer und benachbarte Heizkammern des Retortenofens gemäß Figur 1,

Figur 5 -

eine Einzelheit A, die den Aufbau des feuerfesten Materials mit der Metallblechauskleidung zeigt,

Figur 6 -

eine Einzelheit B eines in Figur 5 dargestellten Zugankers.

The invention will be explained in more detail below with reference to an exemplary embodiment shown schematically in the drawing. Show it:

Figure 1 -

2 shows a longitudinal section through a retort furnace according to the invention,

Figure 2 -

is a schematic view of a front door with pocket segments for sealants

Figure 3 -

a vertical section through a condenser placed on a filling opening,

Figure 4 -

2 shows a cross section through a retort chamber and adjacent heating chambers of the retort furnace according to FIG. 1,

Figure 5 -

a detail A, which shows the structure of the refractory material with the metal sheet lining,

Figure 6 -

a detail B of a tie rod shown in Figure 5.

Figure 1 shows a horizontal chamber furnace 1, the one Substructure 2 and a retort chamber extending over the length 3 has. The retort chamber is on both ends closed by doors 4, 5. Below doors 4, 5 are outside the furnace 1 frames 6, on which one Broaching machine (not shown) or a removal device are movable for clearing ash.

The retort chamber 3 has in the illustrated embodiment 3 filler openings 7 that 8 between ceiling stones are trained.

Capacitors 9 are placed on the filling openings 7 with vacuum lines 10 with each other and with a vacuum source 11 are connected.

FIG. 1 shows that the retort chamber 3 with briquettes 12 filled with a mixture of dolomite lime (CaO · MgO) and ferrosilicon are manufactured, with an upper part of the Retort chamber cannot be filled.

Figure 2 shows a plan view of a front door 4, 5 of the Retort chamber 3. In contrast to corresponding doors on coke ovens Doors 4, 5 on oven 1 according to the invention can be made vacuum tight so that a seal from the outside must be realized internally. This is for example can be achieved by injecting sealant into the sealing joint, is poured or preferably sprayed, the sealant be applied in excess in pasty or liquid form must, so that the sealant under the influence of negative pressure in the retort chamber 3 from the outside into the sealing joint and under the influence of heat in the retort chamber 3 or the door 4, 5 hardens and causes the sealing effect. There sealants run off in liquid form in the area of the door 4, 5 or drip off is the door with pocket-shaped segments 13 provided with which expired sealant 14 is collected can be.

FIG. 3 illustrates the enlarged detail A 'from FIG Structure of an embodiment of a capacitor 9 based on a receptacle 15 formed in the filling opening 7 is placed and is sealed with a seal 16. The recording 15 is from a matched to the housing shape of the capacitor 9 Bevel. The capacitor 9 consists essentially of a the filling opening 7 essentially continuing cylindrical Wall 17, the free top with a cover 18th is lockable. The lid 18 is in the closed position lockable (not shown) and has an eyelet 19 for Lifting the cover 18 or the entire capacitor 9 with the closed, locked lid 18. In the cylindrical Wall 17, an insert 20 is used, which has the shape of a has the cup turned upside down and on the vaporous Magnesium deposits.

The interior of the cylindrical wall 17 is via a line 21 connected to a vacuum connecting flange 22. To the vacuum connection flange 22, a vacuum line 10 (FIG. 1) can be connected.

The cylindrical wall 17 is with a radially outer cylindrical Wall 23 surround that with an inlet port 24 and an outlet port 25 for cooling water is provided, through the the cylindrical wall 17 - and thus the insert 20 - on one Temperature of maximum 100 ° C is cooled down.

FIG. 4 illustrates the heating system for the retort chamber 3, which is carried out in a manner known for coke ovens. The Walls of the retort chamber 3 are made of refractory material 26 formed and separate the retort chamber 3 from both sides adjacent heating chambers 27 from. Be in the heating chamber 27 Fuel gases and combustion air preheated in a recuperator introduced, namely over the length of the heating chambers 27 at several Places that are evenly spaced from each other. Exhaust gases pass through an upper exhaust opening 28, which with refractory Ring stones 29 is formed out of the furnace 1.

The retort chamber 3 is on the inside (with respect to the retort chamber 3) the walls made of refractory material 26 and Bottom of the retort chamber 3 with a sheet metal lining 30 Mistake. The sheet metal lining 30 is supported flat from the walls made of refractory material 26. The attachment to the Walls made of refractory material 26 is filled by the Supported retort chamber 3 with the briquettes 12 of the feed.

In the upper area of the retort chamber 3, which does not have briquettes 12 can be filled, the sheet metal lining 30 is stepped expanded outside and is in an upper section 31 inside of the refractory material 26 led to an invasion of the Sheet metal lining 30 inside, in the area where the briquettes 12 no outward pressure on the sheet metal lining 30 exercise to exclude.

Figure 4 shows that the retort chamber 3 outside the Filling openings 7 with the ceiling stones 8 is closed. The sheet metal lining 30 is above the ceiling stones 8 closed.

The exhaust openings 28 are inside a fireclay cover 32 performed, which covers the furnace 1 outside the capacitors 9.

Figure 5 illustrates the detail in an enlarged view A of Figure 4 on the construction of the walls made of refractory Material 26, which is preferably silica, with the sheet metal liner 30. The walls made of refractory material 26 are made of refractory Composite stones 33 built. The sheet metal liner 30 is with tie rods 34 against the wall made of refractory material 26 biased under train so that the concern of the sheet metal lining 30 on the wall made of fireproof material 26 also guaranteed is when the vacuum is formed within the retort chamber 3 and a high temperature is set.

Since the wall is made of refractory material 26, if it is made of silica there is no thermal expansion between 600 ° and 1200 ° C, the sheet metal lining 30, however, is significantly below Expands heat, beads 35 are provided in the sheet metal lining, which the thermal expansion of the sheet metal lining 30 through their Compensate for enlargement or reduction.

Figure 6 shows the detail B in Figure 5, the sheet metal lining 30 a bolt 36 with an internal thread 37 is welded on is into which a thread of the tie rod 34 can be screwed is, so that the sheet metal lining by screwing the tie rod 34 30 against the shaped blocks 33 of the wall made of refractory Material 26 is pulled.

The drawing shows that the retort furnace according to the invention compared to a conventional coke oven by the attachment the sheet metal lining 30 and the placement of the capacitors 9 is modified on the filling openings 7.

The capacitor 9 can completely after a batch cycle withdrawn to obtain the deposited magnesium become. However, it is also possible to open the cover 18 only to remove the insert 20 and the new loading of the Retort chamber 3 through the opened lid 18 of the capacitor 9 after insert 20 has been removed. In this case can the housing of the capacitor 9 more or less fixed be connected to the wall of the filling opening 7.

Claims (12)

1. A retort oven for producing magnesium by reducing a feed material (12) of oxidic magnesium in particular in the form of dolomitic lime, with the aid of a reducing agent, in particular ferrosilicon, at temperatures ≥ 1000°C and under a low vacuum, characterised by construction in the form of a horizontal chamber oven having at least one retort chamber (3) extending over the longitudinal direction, which chamber (3) is provided with walls of refractory material (26) and an internal vacuum-tight sheet metal lining (30) together with feed openings (7) at the top, heating chambers (27) arranged on both sides along the retort chamber and condensers (9) for cooling magnesium vapour and accommodating condensed magnesium, which may be connected in sealed and vacuum-tight manner to the feed openings (7).
2. A retort oven according to claim 1, characterised in that the condensers (9) are connected to one another and to a vacuum source (11) via vacuum lines (10).
3. A retort oven according to claim 1 or claim 2, characterised in that the condensers (9) are so constructed as to be positionable in vacuum-tight manner on seals (16) of the feed openings (7).
4. A retort oven according to one of claims 1 to 3, characterised in that the sheet metal lining (30) consists of an austenitic steel.
5. A retort oven according to one of claims 1 to 3, characterised in that the sheet metal lining (30) consists of a nickel-based alloy.
6. A retort oven according to one of claims 1 to 5, characterised in that the sheet metal lining (30) is anchored under pretension to the walls of the retort chamber (3) consisting of refractory material (26).
7. A retort oven according to one of claims 1 to 6, characterised in that the sheet metal lining (30) is provided with longitudinal and/or transverse corrugations (35) for compensating thermal expansion.
8. A retort oven according to one of claims 1 to 7, characterised in that the vacuum-tight sheet metal lining (30) is attached to the inside of the walls formed by refractory material (26) in the area of the retort chamber (3) which is filled and in that it passes inside the refractory material (26) in the upper portion (31) of the retort chamber (3).
9. A retort oven according to one of claims 1 to 8, characterised in that the retort chamber (3) is sealed at its top by ceiling stones (8) and in that the sheet metal lining (30) is closed above the ceiling stones (8).
10. A retort oven according to one of claims 1 to 9, characterised by doors (4, 5) of the retort chamber (3), which are arranged at the ends and may be closed in vacuum-tight manner by pasty, pourable or sprayable sealant (14).
11. A retort oven according to claim 10, characterised in that the doors (4, 5) or door frames are provided with pocket segments (13) for catching sealant (14) as it runs or trickles off.
12. Use of a horizontal chamber coking oven as a retort oven for producing magnesium according to one of claims 1 to 11 after lining the retort chamber (3) with the vacuum-tight sheet metal lininc (30) and attaching condensers (9) to the feed openings (7).

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