DE2259219C3 - 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 determined by the properties the vessel materials are limited.

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 furnaces. Such reactions have so far only been carried out at temperatures above 2000 ^° C. in complex 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 inside a refractory lining or infeed finally has devices 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 high-melting products in the furnace succeeds by this material is heated by a plasma or an electric arc until it melts down. It will the furnace rotated about a vertical axis so that the melt forming a liquid wall coating in Forms 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 • speed, heat supply, cooling speed, gas speed and rotation speed of the furnace necessary. By changing these parameters

jo can be dwell time and working temperature as well as the Adjust the discharge speed as required.

The furnace system according to the invention is illustrated in FIGS. explained in more detail.
F i g. 1 is an axial cross-section through a furnace system according to the invention;

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

F i g. 3, 4, 5 and 6 are schematic views of various embodiments of the heating system; the F i g. 7, 8 and 9 show axial sections showing the various possibilities of collection and Let the melt discharge from the furnace floor be seen.

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

■ 15 of an arc that emanates from a plasma jet in the furnace roof to a consuming anode Carbon is guided in the outlet opening of the furnace. The furnace itself consists of the jacket 1 parabolic, cylindrical or other shape, carried by the steel jacket 2 on the roller bearings 3 for the ratation around a vertical axis. The steel jacket 2 is over at variable speed a belt drive driven by the roller 4 (drive motor not shown). The lower part of the The jacket is connected to the tapping part 6 via an insulation 5. The whole furnace vessel is filled with water refrigerated 7. The furnace lining can be of various types and depends on the type of furnace to be used technical process. In a ceramic furnace, the lining consists of a Infeed 8 in the immediate vicinity of the cooled furnace jacket. This ceramic lining is made by a liquid ceramic coating 9 protected, the is held in a stable parabolic shape inside the furnace and is heated by the plasma in the furnace is. The furnace roof consists of a steel cover with a refractory lining to prevent it excessive heat loss. In the one shown in FIG

Embodiment is the heat through a Lichxbogen generated from the plasma burner 10 within the furnace cover. This burner is not after the transmitting principle started by the switch 11 (Fig.2) is closed. Having a stable Plasma has formed, the switch is opened and the circuit is then melted via the adjustable carbon anode 12. The warmth of the plasma in the furnace causes the outermost layer of the furnace lining to melt down to form a stable parabolic film held in place by centrifugal force. By If the rotation speed of the furnace is reduced, the liquid can sink and reach the tap opening 13th

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. If the centrifugal force is reduced, so 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 use a ring made of coated metal or refractory material (not shown) to avoid loss of melt at the top of the parabolic film and 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 withdraw liquid products over the top of the crucible.

The heating option shown in Fig. 1 and 2 is only one of the useful for the furnace system. Man can a direct current plasma alone according to the non-transmitting principle as in FIG. 3 indicated, 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 transmitting or non-transmitting principle between plasma torch and a fixed Electrode (Fig. 2) are generated. In this case, both direct current and alternating current can be used and the transfer can take place between two or more plasma jets (Fig. 5). At a Such an embodiment can be 3 plasma jets, 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 (Figure 4, but with 3 carbon electrodes) for very effective and economical operation, three consumable electrodes made of carbon are provided adjustable. The three-phase arc is struck between the electrodes while they are held together in the center of the furnace. After ignition of the electric arc w gens are moved apart from the electrodes and so withdrawn, that the sheet, as indicated in Figure 4B, satisfies the furnace chamber. A direct current plasma beam can be used to stabilize the arc. Once the innermost layer of the furnace lining has melted, it becomes conductive if it is not cooled. The sheet is then transferred to the thin skin of liquid on the furnace 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) enters the furnace itself is introduced. A similar embodiment can be applied to non-consuming, e.g. B. water-cooled metal electrodes, if so desired.

A variety of other forms of plasma jets with consumable or non-consumable Experts are familiar with electrodes. The use of direct current, single-phase or multi-phase Alternating current is possible. Another possible source of heat is induction heating, either through inductive heating of the furnace content itself or by introducing an inductively heated gas into the furnace will. In the first embodiment, the outer wall of the furnace must be made of insulating material (e.g. silica) exist, while the inner layers, which are initially heated by auxiliary means, become inductive are heated 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. As mentioned, the inner surface can be melted. It will last ceramic material is recharged, this is melted down and leaves the tapping for casting, z. B. for the production of fiber material or the like.

You can also put two or three materials into 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 layer under the centrifugal force. Under these The development of gas takes place under conditions which often lead to serious problems in glass production can, very quickly and the bubbles can by the action of centrifugal force very quickly in the Exit middle zone and thus 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, z. B. in the production of silicon dioxide by reacting Siiiriumtetrachlorid with oxygen.

The material used for the water-cooled furnace shell is usually metal in a parabolic, conical shape or cylindrical shape applied. There can be a liquid in the immediate vicinity of the furnace shell Product, but preference is given to a solid one. In many cases it is in contact with the furnace shell standing layer has the same or similar composition as the liquid inner layer, but it can be underneath be desirable in certain circumstances, e.g. B. because of the high thermal expansion of such materials, in between to provide a massive refractory lining. This enables a longer oven journey, since that The melt flows away inside the furnace only on the surface of the lining and the erosion occurs the refractory lining is kept small.

Just as the charging can take place continuously or discontinuously, so can the discharge be carried out continuously or discontinuously. According to one embodiment and with a corresponding configuration the furnace vessel can be charged with liquid material, then it slows down driven or the movement stopped completely, so that a step-by-step discharge is possible. At a Another mode of operation of the furnace is continuously abandoned and the liquid product continuously deducted.

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 sleeves. Other configurations are possible, e.g. B. as in FIG. 9 shown a forehearth. The liquid flow obtained in this way then goes to further processing, such as quenching to obtain metastable products, granulating, molding. 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., z. 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 Some essentials are explained below. These are simple melting processes of a 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 can be separated, furthermore metallurgical smelting, where 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 1

Melting down a refractory material, e.g. B. Clay

The furnace can be operated with any of the heating types mentioned above. The outer part of the The furnace lining is made of alumina and rests against the cooled furnace shell. The delivery can be stamped be obtained by the slip casting process with a rotating furnace. The furnace will heated with the help of a piasm or an electric arc. the innermost zone of the infeed melts. Then powdered clay is applied, in particular melts at the top and flows downwards through the furnace under gravity. A stream of droplets leaves the oven.

By setting the feed speed, the electricity and the furnace rotation speed accordingly it is possible to adjust the temperature at the furnace outlet or, if discontinuous If process control is desired, this is also possible without further ado. For melting down alumina three different heating systems can be used, 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), current intensity 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 11 opened and all the force now flows to the graphite electrode, which is in the discharge zone of the furnace is withdrawn hydraulically or via a guide thread. The electrical conditions are now 170 V, 210 A, 35.7 kW. After another minute, these parameters have changed stabilized at 110 V. 250 A. 27.5 kW. The latter data correspond to the operating status of the heated furnace. Under these conditions that is Plasma calm, and the current partly goes through the liquid ceramic mass.

Under these conditions there is a continuous feed into the furnace and a continuous exhaust of molten alumina (41.7 g / min) with an energy input of 27.5 kW corresponding to a Power-to-weight ratio of 11 kWh / kg possible. Of course, these are not the optimal values, but you can still achieve improvements in heating performance.

b) 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 the arc was ignited a free-burning arc 116 A. 141V, 16.4 kW maintained. When adjusting the

Electrodes so that the electrode tips come close to the furnace wall (Fig. 4B, without plasma torch), the arc goes over to the molten ceramic material and works steadily and calmly with it 120A, 130V, 15.6 kW. Under these conditions, the alumina lining melts and the melt exits below. The circuit between the two electrodes goes entirely through the two arcs and through the liquid refractory material. This is a very effective way of heating the contents of the oven, 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 specially designed plasma torches are inserted into the furnace lid, which can be itself made from rammed aluminum oxide. The two torches initially work in a non-transmitting manner like conventional plasma torches. After an initial heating, however, the circuit goes in such a way that only one burner works as a conventional burner with the formation of a small production plasma. The second burner works at 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. A large plasma fireball forms inside the furnace. With increasing heating of the furnace contents, an increasing proportion of the current flows between the two burners 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 50 l / min 130 V, 320A,

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. Size Oven units and improved construction lead to significant increases in efficiency

Example 2

Melting a mixture of refractories
materials

A pourable mixture of quartzite, alumina and barium oxide was produced (1500 g SiO2 <0.4mm; g Al ₂ O3 <0.13mm; 300 g 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 made with the aid of plasma up to

Melting of the innermost zone heated. This is continuously achieved by adding more powder mixture renewed with the same composition. The powder mixture reacts on the inner surface and flows as Glass off. The glass emerges at the outlet end, is quickly quenched and results in a fully reacted one Glass material. Crystallization can be brought about by appropriate heat treatment and a glass-ceramic product is obtained. Using heating with 2 plasma torches The following parameters are set during continuous operation:

Production burner:

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

works in nitrogen 50 l / rr.in, 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 reason for the absence of the 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 collect the glass as droplets. You can also run the current continuously pour off (and quench if desired), or the speed of the furnace rotation becomes periodic reduced if there is a large batch of molten glass under this batch management you get cast rods made of glass or ceramic by the melt z. B. cast in graphite molds will. These blanks can then be further processed thermally or mechanically.

Example 3 Vapor Phase Metallurgical Reaction

The furnace lining consists of a finely ground, tin-containing slag mixture, made into a casting slip using an organic Silicic acid ester as a binder. After drying and light firing using plasma heating the slag lining is strongly heated so that the innermost zone is cut off. It is then continuously further fine-grained slag is added and further heated in a neutral atmosphere volatile tin compounds are precipitated from the metal. They escape with the gas flow, the leaves the furnace after blowing in air

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 is - as above - processed into a furnace lining. The furnace is then using a DC arc drawn from the plasma jet from the furnace lid to a carbon electrode, which by tapping into the furnace chamber (Fig. 1) heated until an equilibrium is reached and no Smoke or slag escape. The furnace is then continuous with the tin-containing, finely powdered Slag charged. The vapors are either drawn off through a chimney on the lid of the In the furnace or together with the molten slag via the tap. Preferably one draws the gas atmosphere is naturally removed via the furnace lid. The feed rate 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 air cooled and then essentially pure in a cyclone or filter bag Tin oxide deposited.

The slag discharged from the tap is quenched with water, dried and analyzed 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

40

45

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 The liquid is produced under a high heat supply in a neutral or reducing furnace atmosphere Furnace wall continuously fine powdered alumina and carbon in the finest distribution in approximately supplied to a stoichiometric ratio. Aluminum oxide melts on the furnace lining, settles with it Carbon around and completely volatilized in the form of Al, AI2O and CO. The furnace gases are under quenched in inert conditions. A product is obtained which is or is free aluminum metal is reoxidized to form extremely fine aluminum oxide. It can also be very fine with others refractory powders are implemented. Carbides, nitrides or borides can be produced in this way. This example shows the complete evaporation of a batch and the carbothermal reduction of MciälloXidcn.

Example 5
Metal smelting

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 Qfen fed. Iron oxide is continuously charged, which quickly reduces to metallic iron and formed a layer of enamel that ran down over the furnace's alumina liner and at the same time formed a liquid wall to protect the lining. If desired, you can Add slag former. If the slag is lighter than iron, it forms the innermost layer and stays on the liquid iron, which in turn rests against the refractory lining. The two layers of liquid pull down through the furnace and become then separated in a forehearth or the like. The resulting pig iron can be converted to steel in the usual way are processed. If necessary, you can choose the furnace conditions directly reach a steel.

Ferro alloys can be produced in the same way by reducing the corresponding oxide mixtures. Of course, other metals and their alloys can also be smelted in this way.

The furnace system according to the invention was previously based on a crucible with a vertical axis of rotation and a parabolic, liquid wall explained. Of course, under the same conditions, the axis of rotation can also be slightly inclined to the vertical. The body of revolution of the liquid wall is then not ideally a paraboloid.

To this end, 3 Ölatt drawings

Claims (10)

Patent claims: 1. High-temperature furnace with furnace jacket rotatable around an approximately vertical axis and one refractory Lining, as well as 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 a plasma torch is arranged on the furnace cover and a counter electrode in the furnace tap for heating the furnace contents. 3. High-temperature furnace according to claim 1, characterized in that the plasma torch is arranged eccentrically in the furnace lid. 4. High-temperature furnace according to claim 2, characterized in that there are three in the furnace lid 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 Stability of the arc a direct current plasma torch is provided. 6. Application of the furnace according to one of claims 1 to 5 for melting down a Glass offset or a ceramic material by taking from the offset or the starting mixture the furnace lining produces the innermost zone of the through the heating device The infeed melts, this keeps supplying fresh raw material and finally the Draws off the melt at the discharge. 7. Application of the furnace according to claim 6 with an arc or two 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 deposition of the volatilized metal compounds from the furnace atmosphere, in particular of 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.