DE2259219B2 - High temperature furnace and its application - Google Patents

Description

The invention relates to ovens for treating materials at high temperatures, in particular to the field of metallurgy and ceramics. The working temperatures are often limited by the properties of the vessel materials.

So is z. B. the reaction temperature of a glass offset is often limited by the availability of heat-resistant precious metal alloys. The temperature at which an ore can be melted down is limited by the reaction speed of the slag with the refractory lining material of the furnace. Such reactions have so far only been carried out at temperatures above 2000 ^° C. in expensive and special devices which are unsuitable for large-scale procedures

The invention now relates to a furnace system for treating materials at high temperatures in Form of an outer jacket that can be rotated around a vertical axis and has a refractory inside: lining or lining, finally device gene for rotating the furnace system around the vertical axis as well as feeds for charging, heating options and discharge opening for the reaction material

; - According to the invention, the melting of refractory products in the furnace by passing this material through a plasma or an electric arc It is heated until it melts. The furnace is rotated about a vertical axis so that the the melt that forms a liquid wall coating in the form of a paraboloid of revolution on the inner surface of the furnace

The furnace according to the invention is preferably operated continuously by continuously adding material abandoned and melt is discharged. For this purpose, a corresponding setting of the charging speed, the heat measurement requirement, the cooling speed, the gas speed and the rotational speed of the furnace is required necessary. By changing these parameters, the residence time and working temperature as well as the Adjust the discharge speed as required.

The furnace system according to the invention is explained in more detail with reference to the figure

F i g. 1 is an axial cross-section through a furnace system according to the invention;

F i g. Figure 2 shows a schematic representation of the furnace of Figure 2. 1 with the electrical control circuit; the

Figures 3, 4, 5 and 6 are schematic views different embodiments of the heating system; the F i g. 7, 8 and 9 show axial sections in which see the various options for collecting and discharging the melt from the furnace floor permit.

The furnace system according to FIG. 1 is heated with the help

an arc created by a plasma jet in the

The furnace roof turns into a consuming anode Carbon out in the outlet opening of the furnace

will. The furnace itself consists of the jacket 1 parabolic, cylindrical or other shape,

thus supported by the steel jacket 2 on the roller bearings 3

for ratation around a vertical axis. Of the

Steel jacket 2 is variable speed over

a belt drive is driven by the roller 4 (Drive motor not shown). The lower part of the

The jacket is connected to the taping part 6 via an insulation 5

tied together. The whole furnace vessel is filled with water

chilled 7. The furnace lining can be of the most varied

Be kind and depends on what is to be done

technical process. 3 for a ceramic one

Melting furnace, the lining consists of a Delivery 8 in the immediate vicinity of the refrigerated Oven Manlels. This ceramic lining is made by

a liquid ceramic coating 9 protected, the

stable in a parabolic shape inside the furnace

f> 5 and heated by the plasma in the furnace

is. The furnace roof consists of a refractory

Infeed provided steel cover to avoid

excessive heat loss. In the in F i g. 1 shown

Embodiment is the heat by an arc from the plasma torch 10 within the furnace lid This burner is started on the non-transmitting principle by pressing switch 11 (Fig.2) is closed. Having a stable When the plasma has formed, the switch is opened and the circuit is then set over the adjustable Carbon anode 12 melted. The heat of the plasma in the furnace causes the melting down of the outermost Layer the furnace lining, forming a stable paraboloid film, created by centrifugal force held in place. By reducing the speed of rotation of the furnace, you can the liquid sink and reach the tap opening 13.

The preferred mode of operation, however, is the continuous addition of fresh material, e.g. B. via charging opening 14. In this way the liquid layer is constantly renewed and builds up inside the furnace vessel on. It is held in place by centrifugal force. The centrifugal force is reduced in this way the melt flows off and can be discharged via 13. It is obvious that the system is self-stabilizing and that the speed of the liquid discharge depends on the charging speed depends

In some cases it is necessary to have a ring out coated metal or refractory material (not shown) to prevent loss of melt on the avoid top end of parabolic film and jo to ensure that all of the liquid products can be discharged via the tap 13. It however, there are also cases where it is desirable to draw off liquid products over the upper edge of the crucible.

The heating option shown in Fig. 1 and 2 is only one of the useful for the furnace system. Man a direct current plasma can only use the non-transmitting principle as indicated in FIG use if more intense heating is required by placing the lance eccentrically on the furnace lid is mounted. However, an alternating current arc (not shown) can also be used. The bow can according to the transferring or non-transferring principle between plasma torch and a fixed one Electrode (Fig. 2) are generated. In this case, both direct current and alternating current can be used and the transfer can take place between 2 or more plasma jets (Fig. 5). At a Such an embodiment can be 3 placa rays, Appropriately coming from the furnace lid, operate with direct current. Three-phase alternating current is fed to the burners and causes the contents of the oven to be heated very intensively.

In a further embodiment (FIG. 4, but with 3 carbon electrodes) for very effective and economical operation, 3 consumable electrodes made of carbon are provided in an adjustable manner. The three-phase arc is struck between the electrodes while they are held together in the center of the furnace. After the arc has been ignited, the electrodes are moved apart and withdrawn so that the arc, as indicated in FIG. 4B, fills the furnace space. A direct current plasma beam can be used to stabilize the arc. As soon as the innermost layer of the furnace lining has melted, it becomes conductive if it is not cooled. The bow is then on di. ^{Transfer 1} thin liquid kcitshi Jl onto the oven wall. Then the heating takes place due to the resistance to the passage of current. Under these conditions, the goods are heated very effectively. If the electrodes are continuously readjusted, continuous operation is possible. It is not necessary to pass a gas stream into the furnace when it is operated in this way, but the desired gas atmosphere can be fed into the furnace if necessary. If necessary, it is also possible to work with an oxidizing atmosphere in the furnace, e.g. B. to prevent the evaporation of components from a glass offset. This can also be achieved with a carbon arc as a heat source, but in this case inert gas (e.g. argon or nitrogen) is introduced into a shield surrounding the carbon electrodes while the oxidizing gas (e.g. air or oxygen) is introduced into the furnace itself will. A similar embodiment can be applied to non-consuming, z. B. water-cooled metal electrodes, if this is desired.

A large number of other shapers for blow-molding piasma jets with consumable or consumable electrodes are familiar to experts. The use of direct current, single-phase or multi-phase alternating current is possible. Another possible source of heat is induction heating, either by inductively heating the contents of the furnace itself or by introducing an inductively heated gas into the furnace. In the first embodiment, the outer wall of the furnace must be made of insulating material (e.g. silica), while the inner layers, which are initially heated by auxiliary means, are to be heated inductively with the help of stationary coils around the parabolic furnace vessel (Fig . 6).

The furnace system according to the invention with one or the other type of heating can be used for melting or used to react different materials. In the simplest embodiment, the furnace system is with a? ceramic Lined material The inner surface can be melted, as mentioned. It will last '. Ceramic material is recharged this is melted down and leaves the racking for casting, e.g. B. for the production of fiber material or the like.

You can also add 2 or 3 materials to the furnace and then make them react. Becomes a corresponding oxide mixture abandoned, melted down and converted to form the liquid wall, see above a good conversion and homogenization of the melt is achieved, which is particularly useful in of glass production for fiber optic production.

The extremely high temperatures in the furnace mean that implementation is very rapid and high performance, which is particularly important for glass production. The reaction takes place instead of in a thin layer, namely as a non-viscous one Layer under centrifugal force. Under these conditions, the gas evolution takes place, which in the Glass making can often lead to serious problems very quickly and the bubbles can get through that Under the effect of centrifugal force, exit very quickly in the central zone and thus the hottest zone.

While the task of solids is of the greatest importance for the application of these furnace systems », it is also possible to introduce liquid reactants and even gases under certain circumstances.

It may be desirable to use a melt from another process, e.g. B. a metallurgical

Slag, treat, or it may be desirable to have gaseous products on the liquid walls simply by condensation or condensation due to chemical reaction, / .. B. in the production of silicon dioxide by reacting silicon tetrachloride with oxygen.

Metal in parabolic, conical or cylindrical shape is usually used as the material for the water-cooled furnace shell. There may be a fliis <; ij? E% product in the immediate vicinity of the furnace shell, but a festos is preferred. In many cases the layer in contact with the furnace shell will have the same or similar composition as the liquid inner layer, but in certain circumstances it may be desirable, e.g. B. because of the high thermal expansion of such materials, to provide a massive refractory lining in between. This enables'. ! ϊ>? ^η pine längrrp furnace travel, since the melt flow inside the furnace only takes place on the surface of the lining and the erosion on the refractory lining is kept small.

', o like charging continuously or discontinuously can take place, the discharge can also take place continuously or discontinuously. To According to one embodiment and with a corresponding configuration of the furnace vessel, the furnace can be filled with liquid Material are charged, then it is driven more slowly or the movement is stopped completely, so that a batch-wise discharge is enabled. Another mode of operation of the furnace is continuous abandoned and the liquid product withdrawn continuously.

The liquid leaves the discharge as a stream or curtain of droplets, with the droplets at an angle to the outside under the influence of the rotation of the discharge. This is not wanted, it is one strives for a regulated flow that can be achieved through a cylindrical collecting cuff, which can be water-cooled and has a lining like the furnace vessel. The F i g. 7 and 8 show Embodiments of such guide cuffs; s others Refinements are possible, e.g. B. as in FIG. 9, a forehearth. The liquid stream thus obtained then goes to further processing such as quenching to obtain metastable products. Granulate. To shape. Fiber manufacture or the like.

As pointed out above, gases or form the second important class of products Fumes. These can be extracted from the furnace lid or from the discharge for the liquid Product can be obtained. Under certain circumstances, e.g. B. for a metallurgical gas phase reaction, it may be necessary to treat a steam with a reaction gas (e.g. air or oxygen), to obtain a fine oxide powder which is cooled and discharged in the usual way.

It is obvious that the furnace system according to the invention is suitable for a wide variety of processes. in the Some essentials are explained below. It is a simple melting process refractory component, a melting of a mixture of refractory components so that a Reaction takes place and a material is obtained which can serve as glass or ceramic; finally, metallurgical gas phase reactions in which one or more volatile components of liquid slag or ore are separated, furthermore metallurgical smelting processes, whereby an oxide, a Oxide mixtures or other metal compounds are reduced to molten metal. Look at this Application examples should also be used to explain the various heat sources.

Example I.

Melting down a refractory material, / .. B. Clay

The oven can be operated with any of the above mentioned heating systems. The outer part of the The furnace lining consists of alumina and rests against the cooled furnace shell. The delivery can be stamped or after the slip pouring process rotating furnace. The furnace is heated with the help of a plasma or an electric arc. the innermost zone of the infeed melts. Then powdered clay is applied, in particular flows down through the furnace under the force of gravity. A stream of droplets leaves the oven.

By setting the feed rate accordingly. the current energy and the speed of rotation of the furnace, it is possible to set the temperature at the furnace outlet or, if discontinuous measurement is desired, this is also possible without further ado. Three different heating systems can be used for melting down alumina, namely:
a) Plasma jet according to the transferring principle:

A plasma jet was from the lid in a non-transferring state with argon (3 l / min), amperage 265 A, voltage 35 V. The electrical circuit is indicated in FIG. To one minute the arc was transferred to the graphite electrode 12, which extends through the crucible of extends down into the furnace chamber by adjusting the resistance in the circuit between the anode and the switch 11. As soon as the plasma jet is transmitted, the switch II opened and all power flows, · .... - "u der Graphite electrode that is placed in the discharge zone of the furnace hydraulically or via a guide thread is withdrawn. The electrical conditions are now 170 V. 210 A. 35. 7 kW. After a For a further minute these parameters have stabilized at 10 V. 250 A, 27.5 kW. The latter data correspond to the operating status of the heated furnace. Under these conditions! As ι Plasma quiet, and the electricity goes partly through that liquid ceramic mass.

Under these conditions there is a continuous feed into the furnace and a continuous exhaust of molten toners (41.7 g / min) under one; Energy consumption of 27.5 kW corresponding to one Power-to-weight ratio of 11 kWh / kg possible. These are of course not the optimal values, but you can still achieve improvements in the heating performance. d) carbon arc

Continuous melting down using a carbon arc as a heat source is possible. to a 2-electrode direct current carbon arc unit is used for this purpose, which is inserted into the furnace lid. The two electrode tips are brought together (Fig. 4A, without plasma torch) and so ignited the arc. A free-burning arc 116 A, 141V, 16.4 kW maintained. When adjusting the

Electrodes so that the electrode tips are close to the When the furnace wall approaches (Fig. 4B. Without plasma torch), the arc passes over to the molten one Ceramic material and works stably and quietly with 120A, 130 V. 15.6 kW. Under these conditions the alumina stalemg melts off and the melt at the bottom. The circuit between the two Electrodes goes completely over the two arcs and through the liquid refractory material. this is a very effective way of heating the contents of the oven. and / was this applies to both single-phase and multi-phase alternating currents.

c) 2 plasma burners

In the third experimental unit, alumina can be continuously melted down in the case of a transferring Arc between 2 burners, as shown schematically in FIG. 5 is shown.

Two special designed plasma torches are used inserted into the furnace lid, which itself can be made from rammed aluminum oxide. The two torches initially work in a non-transmitting manner like conventional plasma torches. However, after initial heating, the circuit goes such that only one burner is more common Brenner works with the formation of a small production plasma. The second burner is working on a cathodic potential compared to the first. In this way the electron flow goes from the Cathode in the form of the second burner to the anode in the form of the first, i.e. production burner. It a large plasma fireball forms inside the furnace. With increasing heating of the oven contents an increasing proportion of the current between the two burners flows through the melt and not so much through the gas phase, which significantly improves the heat transfer. If the operation is stable, the following results

Parameter:

Production burner:

works in argon 40 l / min. 25 V. 132 A. 3.3 kW. Transferring arc:

works under nitrogen 501 / min 130 V, 32OA.

42.3 kW.
Alumina charging:

continuously 0.9 kg / h.
Power consumption, based on fused alumina:

51 kWh / kg.

It should be noted that the above data are derived from small, suboptimal laboratory ovens. Large furnace units and improved construction lead to significant increases in efficiency.

Example 2

Melting down a mixture of refractory materials

A pourable mixture of quartzite. Alumina and barium oxide were produced (1500 g SiO2 <0.4mm; 1200g Al2O ₃ <0.13mm; 300g finest barium oxide) by mixing with water; the pourable slip is poured into a rotary oven. After turning the oven overnight, it was turned off. The ceramic mass, which had now set, was allowed to air dry. It was lightly fired by plasma heating in situ at about 800 ° C. Finally, the fired lining is heated with the help of plasma until the innermost zone melts. This is continuously renewed by adding more powder mixtures of the same composition. The powder mixture reacts on the inner surface and flows off as glass. The glass emerges at the exit end, is quickly quenched and results in a completely reacted glass material. Crystallization can be brought about by appropriate heat treatment and a glass-ceramic product is obtained. When heating with 2 plasma torches, the following parameters are set in continuous operation:

Production burner:

works in argon 40 l / min. 25 V. 180 A, 4.5 kW. Transferring arc:

works in nitrogen 50 l / min. 150 V. 300 A. 45 kW. Task on liquid ceramic product:

"3.3 kg / h.
Power consumption:

27 kWh / kg.

This is also a small laboratory furnace.

Of particular interest is the possibility of producing fully reacted glass products with a high Throughput. In particular, the above-mentioned glass offset can only be carried out with difficulty using conventional methods realize. After continuous operation for a certain period of time, the crystal-clear droplets, obtained by quenching with water, essentially free of bubbles. The blistering at known glass manufacturing processes pose significant problems. The green I for the absence of bubbles lies in that the implementation and melting down of the glass offset high on the parabolic wall of the Crucible takes place, that is in an area of very high temperature and high acceleration due to the Oven rotation. Under these conditions, the glass has a low viscosity and the gas bubbles can easily escape by centrifugal action.

It is not necessary to use the glass as droplets collect. The stream can also be poured off continuously (and, if desired, quenched), or else the speed of the furnace rotation is periodically slowed down when a large batch of glass melts is present. Under this intermittent management, cast rods made of glass or ceramic are obtained, by the melt z. B. is poured into graphite molds. These blanks can then be thermally or further process mechanically.

Example 3 M metallurgical vapor phase reaction

The furnace lining consists of a finely ground, tin-containing slag mixture, mixed with a casting slip using an organic silicic acid ester as a binder. After drying and light burning with the use of plasma heating, the slag lining is strongly heated, so that the innermost zone melts. Finely divided slag is then continuously added and further heated in a neutral atmosphere. The volatile tin compounds are released from the metal eliminated. They escape with the gas stream which leaves the furnace after air has been blown in.

The tin compounds are now converted into fine, voluminous tin oxide, which in cyclones or

Filter bags or electrostatic dust collectors can be obtained.

This method works as follows: Containing a lean tin slag 2.41% tin, becomes - as above - a furnace lining processed. The furnace is then withdrawn from the plasma jet with the aid of a direct current arc from c '? m furnace lid to a carbon electrode, which extends through the tapping into the furnace chamber (Fig. 1) heated until equilibrium is reached and no smoke or slag escape. The oven will then continuously charged with the tin-containing, finely powdered slag. The fumes will be either by drawing off through a chimney on the lid of the furnace or together with the molten slag caught on the rack. Preferably, of course, the gas atmosphere is drawn off via the furnace lid. The feed speed was 52 g / min, power consumption 31.5 kW, corresponding to a power consumption, based on slag, of 10.1 kWh / kg. The furnace gases are cooled with air and then in one Cyclone or a filter bag deposited the essentially pure tin oxide.

The slag discharged from the tap is quenched with water, dried and analyzed. One such slag contained 0.41% tin under these conditions, indicating that 83% des the original tin content of the slag could be recovered in this way. The yield shows that approximately 100% of the volatile tin compounds are recovered in the cyclones or filter bags could. The electricity demand in a small furnace was 505 kWh / kg tin.

In the same way, slag containing lead and zinc can be processed under reducing conditions, so that the metal oxides can be obtained from the furnace atmosphere. In some cases it is advantageous to use this vapor phase reaction in the presence of sulfides, chlorides or other substances Increase the volatility of the metals.

Example 4

Evaporation of a ceramic material -
carbothermal reduction

In the furnace according to the invention, a ceramic substance can be removed from the liquid state evaporate completely. The furnace lining was made of alumina material by slip casting manufactured. With a high supply of heat in a neutral or reducing furnace atmosphere, the furnace becomes liquid Furnace wall can consist of finely powdered alumina and carbon in the finest distribution in approximately supplied stoichiometric ratio. Aluminumo ■ *> xid melts on the furnace lining, reacts with carbon and completely evaporates in Form of Al, AbO and CO. The furnace gases are quenched under inert conditions. One receives a Product which is free aluminum metal or it

in is reoxidized to form extremely fine aluminum oxide. It can also be implemented with other very fine refractory powders. Carbides, nitrides or borides can be produced in this way. This example shows the complete evaporation

i ". of an approach and the carbothermal reduction of Metal oxides.

Example 5 Mol'jlli / t.rl-iMt ti JtId

in "'" ~ "" ^p

The furnace was lined with a refractory material, e.g. B. alumina, magnesite or the like. With a high supply of heat and a reducing atmosphere, natural gas is used as the reducing agent

r> furnace fed. Iron oxide is charged continuously, which was reduced very quickly to metallic iron and formed a layer of enamel that covered dit Alumina lining runs down the furnace while also protecting a liquid wall Notification made. Slagging agents can be added if desired. Is the slag lighter than Iron, it forms the innermost layer and remains on the liquid iron, which in turn is attached to the refractory lining. The two layers of liquid pull down through the furnace and become then separated in a forehearth or the like. The pig iron obtained can be deposited on steel in the usual way are processed. If necessary, you can choose the furnace conditions directly

jo a steel.

Ferro alloys can be passed through in the same way Reduction of the corresponding oxidizers: produce a mixture. Of course you can also use other metals and smelt their alloys in this way.

■! · -> The furnace system according to the invention was previously used on a crucible with a vertical axis of rotation and a parabolic, liquid wall. Of course you can under the same conditions, the axis of rotation can also be inclined slightly to the vertical. The solid of revolution

w the liquid wall is then not ideally a paraboloid.

For this purpose 3 sheets of drawings

Claims (10)

Patent claims: 1. High-temperature furnace with furnace jacket rotatable around an approximately vertical axis and one refractory Lining and means for rotating the furnace, for charging and tapping and means for Heating of the furnace contents, characterized in that in the operating state the liquid Melt or reaction product from the material to be processed, a liquid wall of the furnace forms. 2. High-temperature furnace according to claim 1, characterized in that for heating the A plasma torch is placed on the furnace lid and a counter electrode is placed in the furnace tap are. 3. High-temperature furnace according to claim 1, characterized in that the plasma torch is arranged exzemjräch in the furnace lid. 4. Hochtcrnperaftir furnace according to claim 2, characterized in that the furnace lid 3 is Consuming carbon electrodes are provided and these are used for igniting the arc are adjustably mounted. 5. High-temperature furnace according to claim 4, characterized in that to improve the Arc stability is provided by a DC plasma torch 6. Application of the furnace according to one of claims 1 to 5 for melting down a Glass offset or a ceramic material, in that n <an from the Versau or the initial mixture produces the furnace allocation through which Heating device melts the innermost zone of the lining, this always fresh Feeds in the starting material and finally withdraws the melt at the discharge point 7. Application of the furnace according to claim 6 with an arc or 2 plasma torches, wherein one is the working burner and the other has cathodic potential for it 8. Use of the furnace according to one of claims 1 to 5 for smelting metal-containing Slag due to the separation of the volatilized metal compounds from the furnace atmosphere, especially tin, zinc or lead. 9. Application of the furnace according to one of claims 1 to 5 for metal volatilization under carbothermal reduction. 10. Use of the furnace according to one of claims 1 to 5 for smelting metal-containing Materials such as ores, possibly with slag formers.