DE2259219A1 - HIGH TEMPERATURE OVEN AND ITS APPLICATION - Google Patents

Description

High temperature furnace and its application

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

This is e.g. the reaction temperature of a glass offset often limited by the availability of heat-resistant precious metal alloys. The temperature at which an ore will 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 complex and special devices that are used on a large scale Procedures are unsuitable, carried out.

The invention now relates to an oven system for treatment of materials at high temperatures in the form of an external

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jacket that can be rotated around a vertical axis and has a refractory lining or lining on the inside, Finally, devices for rotating the furnace system around the vertical axis as well as feeds for charging, heating options and discharge opening for the reaction mixture.

According to the invention, the melting of high-melting products in the furnace succeeds in this material through a plasma or an electric arc is heated until it melts down the furnace is rotated around a vertical axis, so that the melt forming a liquid wall coating in the form of a paraboloid of revolution on the inner surface of the furnace forms.

The furnace according to the invention is preferably continuous operated by continuously giving up material and discharging melt. A corresponding setting of Charging speed, heat supply, cooling speed, gas speed and rotation speed of the furnace are required. By changing these parameters, the residence time and working temperature as well as the discharge speed can be adjusted depending on Set wish.

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

FIG. 1 is an axial cross section through a furnace system according to the invention;
FIG. 2 shows a schematic representation of the furnace from FIG

Fig. 1 with the electrical control circuit.

Figures 3t, 4, 5 and 6 are schematic views of various Execution forms of the heating system.

Figures 7, 8 and 9 show axial sections showing the various possibilities of collection and discharge the melt can be seen from the furnace floor.

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

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Arc created by a plasma jet in the furnace roof Sacrificial anode made of carbon led into the outlet opening of the furnace will. The furnace itself "consists of the jacket 1 parabolic, cylindrical or other porin, held by the steel reinforcement 2 on roller bearings 3 for rotation about a vertical axis. The reinforcement cylinder 2 is driven via a variable speed transmission through the roller 4 (drive motor not shown). The lower part of the coat is provided with the abutment part 6 via an insulation 5. The entire furnace vessel is cooled with water. 7. The furnace lining can be of the most varied types and depends on the technological process to be carried out. With a ceramic Melting furnace, the lining consists of a lining 8 in the immediate vicinity of the cooled furnace shell, and this ceramic Infeed is protected by a liquid ceramic coating 9, which is kept stable inside the furnace parabolic porm and is heated by the plasma of the furnace. The furnace roof consists of a refractory lining Steel ceiling to avoid excessive heat loss. In the in Pig. The embodiment shown in FIG. 1 is presented by the heat a detached arc from the plasma lance 10 inside the furnace lid. This lance is not lifted off started by closing switch 11 (Pig. 2). After a stable plasma has formed, the The switch is opened and the circuit is then closed via the adjustable carbon anode 12. The warmth of the plasma in the OferT causes the outermost layer of the furnace lining to melt down forming a stable paraboloid pilm that held in place by centrifugal force. By If the rotational speed of the furnace is reduced, the liquid can sink and reach the tap opening 13. The preferred one However, the method of operation is the continuous addition of fresh goods, e.g. via charging opening 14. In this way the plussiness layer is constantly renewed and builds up inside the furnace vessel. It is made by centrifugal force kept at the delivery. If this is reduced, the melt flows off and can be discharged via 13 ".

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It is obvious that the system is self-stabilizing and that the rate of liquid discharge is dependent on the charging speed.

In some cases it is necessary to make a ring coated metal or refractory material (not shown) to prevent loss of melt at the top of the to avoid parabolic film and to ensure that all of the liquid products are discharged via the tap 13 can be. However, there are also instances where it is desirable to have liquid products over the top periphery of the crucible deduct.

The heating option shown in FIGS. 1 and 2 is only one of those useful for the furnace system. One can Direct current plasma alone in the non-lifted form (nontransferred mode) as indicated in Fig. 3, use if more intensive heating is required by the lance is mounted eccentrically on the furnace lid. However, an alternating current arc (not shown) can also be used. The arch can transmit or be lifted between the plasma lance and a fixed electrode (Fig. 2). In this case both direct current as well as alternating current, and the transmission (transfer) can take place between 2 or more plasma jets (Fig.5). In such an embodiment, 3 plasma jets, Appropriately coming from the furnace lid, operate with direct current. Three-phase alternating current is supplied to the lances 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 sacrificial electrodes are adjustable and made of carbon. The three-phase arc is struck between the electrodes while they are held together in the center of the furnace will. After igniting the arc, the electrodes are moved apart and withdrawn so that the arc, as in Fig. 4B indicated, the furnace chamber met. A direct current plasma beam

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? 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 bow will then transferred to the thin skin of liquid on the furnace wall. Then the heating takes place by resistance through the passage of current. Under these conditions a very effective one takes place Heating of the goods. If the electrodes are continuously readjusted, continuous operation is possible. It is it is not necessary to pass a gas stream into the furnace when it is operated in this way, but the Supply the desired gas atmosphere to the furnace - If necessary, can also be used with an oxidizing atmosphere in the furnace, e.g. to prevent the evaporation of components from a Glass offset. This can also be achieved with a carbon arc as 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. A similar Embodiment can be applied to non-consuming, e.g. water-cooled metal electrodes if desired.

Using a variety of other forms of plasma jets Experts are familiar with sacrificial electrodes or stable electrodes. The use of direct current, single-phase or multi-phase alternating current can be determined. Another possible one The heat source is the induction heating, either by inductive heating of the furnace contents themselves or by an inductively 'heated one Hot gas is introduced into the furnace. In the first embodiment, the outer wall of the furnace must be made of insulating material (e.g. Quartz), while the inner layers, which are initially heated by auxiliary means, have 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 The type of heating can be used to melt or react in a wide variety of ways Materials are used. In the simplest

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The embodiment is the furnace system with a ceramic material lined. As mentioned, the inner surface can be melted. Ceramic material is constantly being recharged, this is melted down and leaves the tapping point for casting e.g. for fiber material or the like.

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

Reached by the extremely high temperatures prevailing in the furnace very fast implementation and high performance, which is particularly important for glass production. The reaction takes place in a thin layer, namely as a non-viscous layer under the centrifugal force. Under these conditions the gas evolution takes place during glass production It can often lead to serious problems very quickly and the bubbles can be caused by the action of centrifugal force very much quickly enter the central zone and thus the hottest zone.

While the abandonment of solids is of greatest importance to the application of these oven system stones can also be liquid Bring in reactants and even gases under certain circumstances.

It may be desirable to treat a melt from another process, e.g. a metallurgical slag, or it may be desirable to have gaseous products on the liquid walls simply by a condensation or a To make condensation due to a chemical reaction, e.g. in the production of silicon dioxide by reaction of silicon tetrachloride with oxygen.

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The material used for the furnace shell is usually water-cooled Metal in parabolic, conical or cylindrical Form applied. A liquid product can be present in the immediate vicinity of the furnace shell, but a solid one is preferred. In many cases it is in contact with the furnace shell Layer has the same or similar composition as the liquid inner layer, but may be desirable under certain circumstances e.g. because of the high thermal expansion of such materials, a massive refractory lining is to be provided in between. This enables a longer oven journey as the Melt inside the furnace only takes place on the surface of the lining and the erosion on the refractory lining was kept small is.

Just as the charging takes place continuously or intermittently can, the discharge can also be continuous or intermittent take place. According to one embodiment and with a corresponding configuration of the furnace vessel, the furnace can be "filled" with liquid material, then it is driven more slowly or the movement is stopped completely, so that an intermittent discharge is possible, In a different mode of operation of the furnace, it is continuously fed and the liquid product continuously withdrawn.

The liquid leaves the discharge as a stream or curtain of droplets, with the droplets below at an angle to the outside exit the influence of the rotation of the discharge. This is not desirable, but one strives for a regulated current, which can be reached through a cylindrical collecting collar, which can be water-cooled, and a lining like the furnace vessel owns. Figures 7 and 8 show possibilities of such guide sleeves. Other configurations are possible, e.g. as shown in Fig. 9, a forehearth. The liquid stream thus obtained then goes to further processing, such as quenching metastable products, granulating, molding, fiber manufacturing or the like.

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As noted above, the second is important Class of products gases or vapors, these can be about a discharge can be obtained from the furnace lid or from the discharge for the liquid product. Under certain circumstances, e.g. for a metallurgical gas phase reaction, it may be necessary be able 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 following ^ some essentials are explained. These are simple melting processes of a refractory component, a Melting 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 metal melts. Based on these application examples, the different heat sources are explained.

example 1

Melting down a refractory material, ζ · Β · Alumina:

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

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By setting the gas speed accordingly, the Electricity and the speed of rotation of the furnace it is possible. set the temperature at the furnace outlet or, if intermittently If process control is desired, this is also readily possible possible. There are three possible purely for melting down alumina use different heating systems, namely:

a) transferred arc

A plasma jet was from the ceiling in non-transferred mode with argon (3 l / min), current intensity 265 A, voltage 35 V. The electrical circuit is in Pig. 2 indicated. After a minute it was the sheet is drawn off to the graphite electrode 12, which extends through the crucible from below into the furnace space, and by setting the resistance in the circuit between the anode and the switch 11. As soon as the arc is withdrawn is, the switch 11 is opened and the entire force now flows to the graphite electrode, which is in the discharge zone of the furnace hydraulically or via a guide thread is withdrawn. The electrical conditions are now 170 Y, 210 A, 35.7kW. After another minute have these parameters stabilize at 110 Y, 250 A, 27.5 kW.

the latter data according to the operating status of the heated furnace. In these conditions the plasma is 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 withdrawal of molten material Alumina (41.7 g / min) is possible with an energy consumption of 27.5 kW, corresponding to a power-to-weight ratio of 11 kWh / kg. That are of course not the optimal values, but you can still achieve improvements in the heating performance.

b) carbon arc,

Continuous melting down with the help of a coal arc as a heat source is possible. A 2-electrode direct current carbon arc unit is used for this purpose, which is inserted into the

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Furnace lid is used. The "two electrode tips will be brought together (Fig. 4A, without plasma lance) and ignited the arc. It became a free-burning arc 116 A, 141 V, 16.4 kW maintained. When adjusting of the electrodes so that the electrode tips come close to the furnace wall (Pig. 4B, without plasma lance), the arc goes over on the melted ceramic material and works stably and quietly with 120 A, 130 V, 15.6 kW. Under these conditions the alumina lining melts and the melt emerges from the bottom. The circuit between the two electrodes is complete via the two arcs and by conduction through the liquid refractory material. This is a very effective type of heating of the furnace content, this applies to both single-phase and multi-phase alternating currents

c) 2 piasma lances

In the third experimental unit, alumina can be melted down continuously with an arc drawn between 2 lances, as shown schematically in FIG.

Two specially designed plasma lances are inserted into the furnace lid introduced, which can be self-made from tamped aluminum oxide. The two lances work in first not peeled off like usual Piasmalanzen. Hach one initial heating, however, the circuit goes in such a way that only one lance than the usual lance with the formation of a small one Production plasma is working. The second lance works at a cathodic potential compared to the first. To this The electron flow goes from the cathode in the form of the second lance to the anode in the form of the first, i.e. production lance. A large plasma fireball forms within of the furnace. As the contents of the furnace heat up, an increasing proportion of the current flows between the two Lances through the melt and not so much through the gas phase, which significantly improves heat transfer.

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The following parameters result when the working method is stable:

Production lance: works in argon 40 l / min, 25V> 132 A,

3.3 kW *

Detached sheet: works under nitrogen 50 l / min,

130 V, 320 A, 42.3 kW.

Alumina charging: continuously 0.9 kg / h; Electricity consumption, based on fused alumina: 51 kWh / kg.

. It should be noted that the above data differ from small, derive sub-optimal laboratory furnace. Large furnace units and improved Construction lead to significant increases in effectiveness

Example 2

Melting a mixture of refractory materials:

A pourable mixture of quartz, alumina and barium oxide was produced (1500 g SiO ₂ <0.4 mm; 1200 g Al ₂ O, <0.13 mm; 300 g finest barium oxide) by mixing with water, and the pourable slip "in After turning the furnace overnight it was switched off. The ceramic mass, which had meanwhile solidified, was allowed to dry in the air. It was ^{lightly fired by plasma heating in situ at about 800 °} C. Finally, the fired lining is made with the help of plasma up to Melting of the innermost zone is heated. This is continuously renewed by adding more powder mixture of the same composition. The powder mixture reacts on the inner surface and flows off as glass. The glass emerges at the outlet end, is quickly quenched and results in a completely reacted glass material Heat treatment and crystallization result in a desired glass-ceramic product using heating with 2 plasma The following lances arise during continuous operation

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parameter on:

Production lance: works in argon 40 l / min, 25 V, 180 A #

4.5 kW.

Pulled sheet: works in nitrogen 50 l / min, 150 V,

300 A, 45 kW.

Feed of liquid ceramic product: 3.3 kg / h. Power consumption: 27 kWhAg

This is also a small laboratory furnace.

The possibility of producing "fully reacted glass products with a high throughput" is of particular interest Difficult to implement methods. After continuous operation for a certain period of time, the crystal-clear droplets, obtained by quenching with water, essentially free of bubbles. The blistering is a problem in known glass manufacturing processes The reason for the absence of the bubbles is that the implementation and the Melting down of the glass offset takes place high on the parabolic wall of the crucible, which is very much in one area high temperature and high acceleration due to the furnace rotation. Under these conditions, the glass has low viscosity and the Gas bubbles can easily escape by centrifugal force.

It is not necessary to collect the glass as droplets. The stream can also be poured off continuously (and quenched if desired), or the speed of the furnace rotation can be reduced periodically when a large batch of molten glass is present. Under this absolute management, cast rods made of glass or ceramic are obtained by pouring the melt into graphite molds, for example. These blanks can then be further processed thermally or mechanically.

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Example 3

Metallurgical vapor phase 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 melts. It is then continuously added further finely divided slag and in neutral Atmosphere further heated. The volatile tin compounds are precipitated from the metal. They escape with the gas flow, which leaves the furnace after blowing in air. The tin compounds are now converted into fine, voluminous tin oxide, which is contained within a cyclone or bag filter units or electrostatic dust collectors. ■

The mode of action of this procedure results from the following: A lean tin slag containing $ 2.41 tin will - like above - processed into a furnace lining. The furnace is then withdrawn from the plasma jet with the aid of a direct current arc from the furnace lid to a carbon electrode, which extends into the furnace chamber through the tapping (Pig. 1), heated to an equilibrium is reached and no smoke or slag escapes. The furnace is then continuously charged with the tin-containing, finely powdered slag, and the vapors are collected either by being drawn off through a chimney on the lid of the furnace or together with the molten slag via the tap. Preferably one draws the gas atmosphere naturally over 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 cooled with air and then deposited the essentially pure tin oxide in a cyclone or a bag filter. ..

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The slag discharged from the tap is quenched with water, dried and analyzed. Such a slag contained 0.41 % tin under these conditions, from which it can be seen that 83 ⁰ A of the original tin content of the slag could be obtained in this way. The yield shows that approximately 100 % of the volatile tin compounds could be recovered in the cyclones or bag filters. The electricity demand in a small furnace was 505 kWh / kg tin.

In the same way lead- and zinc-containing slugs can be processed under reducing conditions, so that one can get out the furnace atmosphere can receive the metal oxides. In some cases it is advantageous to have this vapor phase reaction in the presence of sulfides, chlorides or other substances to 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 completely evaporated from the liquid state. the The furnace lining was produced from a material containing alumina by slip casting. With high heat supply at neutral or reducing furnace atmosphere becomes the liquid furnace wall continuously fine powdered alumina and carbon in the finest Distribution supplied in an approximately stoichiometric ratio. Aluminum oxide melts on the furnace lining, reacts with carbon and completely volatilizes in Form of Al, A ^ O and CO. The furnace gases are under inert Conditions deterred. A product is obtained which is free aluminum metal, or it is reoxidized too extraordinarily fine alumina. It can also be implemented with other very fine refractory powders. Carbides, Nitrides and borides can be produced in this way. This example shows the complete evaporation of a batch

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and the carbothermal reduction of metal oxides.

Example 5

Metal smelting:

The furnace was lined with a refractory material, for example aluminum oxide, magnesite or the like. Natural gas is fed into the furnace as a reducing agent with a high supply of heat and a reducing atmosphere. Iron oxide is charged continuously, which was reduced very quickly to metallic iron and formed a layer of melt "that runs down over the aluminum oxide lining of the furnace and at the same time forms a liquid wall to protect the lining. If desired, slag forming agents can be added Slag lighter than iron, it forms the innermost layer and remains on the liquid iron, which in turn rests on the refractory lining. The two liquid layers pull down through the furnace and are then separated in a forehearth or the like ^1. If necessary, a steel can be obtained directly by appropriate selection of the furnace conditions.

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 has so far been on a Seal with a vertical axis of rotation and a parabolic, liquid one Wall explained. Of course, under the same advance. The axis of rotation may also be inclined slightly to the vertical. The solid of revolution of the liquid wall is then not ideal a paraboloid.

Patent to Proverbs 309824/1079

Claims (9)

Claims 1. High-temperature furnace with furnace jacket rotatable around one about vertical axis and a refractory lining as well as means for rotating the furnace, for charging and for tapping and means for heating the furnace contents, characterized in that the liquid melting or Reaction product from the material to be processed forms a liquid wall of the furnace, 2. High-temperature furnace according to claim 1, characterized in that the means for Heating of the furnace contents is a plasma lance on the furnace lid and a counter electrode is provided in the furnace tap. 3. High-temperature furnace according to claim 1, characterized in that as a means for heating in the Furnace cover a plasma torch is provided, in particular eccentric to the furnace cover. 4. High-temperature furnace according to claim 2, characterized in that as heating means in the furnace lid 3 carbon sacrificial electrodes are provided and these can be adjusted accordingly for igniting the arc are mounted. 5. High-temperature furnace according to claim 4, characterized in that to improve the stability of the arc means for a direct current plasma jet are provided. . '■ ϊ 309824/1079 * U-42. 345 6. Application of the furnace according to claim 1 to 5 for melting down of a glass offset or a ceramic material. by making the furnace lining from the offset or the starting mixture produces the innermost zone through the heating means the infeed melts and this repeatedly feeds fresh raw material and finally the melt at the discharge deducts, "·. 7. Application of the furnace according to claim 6 with "an arc or 2 plasma lances as heating means, one being the working lance and the other being the cathodic potential owns. 8. Use of the furnace according to claim 1 to 5 for smelting of metal-containing slag by separating the volatilized metal compounds from the furnace atmosphere, in particular of Tin, zinc or lead, 9. Use of the furnace according to claim 1 to 5 for metal volatilization under carbothermal reduction, 10 * Use of the furnace according to claims 1 to 5 for the smelting of metal-containing materials, such as ores, optionally with slag formers, 4/1079 ' Blank page