EP0292469B1 - Process and apparatus for high-temperature chemical operations - Google Patents

Abstract

Method for melting or melt reducing chemical mixtures at temperatures which exceed the melting temperatures of highly-refractory linings. The method requires the steps of pressing the chemical mixture into bars and arranging the bars to form a cavern having a defined geometry. The cavern surrounds a centrally located high energy density radiation source. The portion of the bar facing the radiation source melts at a certain melting rate. The cavern geometry is maintained by radially advancing the bars toward the radiation source at the same rate as the melting rate.

Description

The present invention relates to a method and to an apparatus for carrying out hot-chemical processes, in particular a melt and / or melt reduction of batches from metallurgical dusts, ores and other materials which can be melted and / or melted, such as e.g. SiO₂, MgO, TiO₂, Ta₂O₅ or the corresponding metals, at working temperatures above the melting temperature of the refractory lining.

It is not possible to carry out hot chemical processes in temperature ranges which are above the melting temperature of the known refractory bricks with the currently available methods. In addition, the currently common smelting and smelting reduction processes have a high energy requirement and, due to the rod discharge contained in the exhaust gases, lead to a serious impairment of the environment, provided that additional equipment which is not expensive is provided. The smelting of smelter dust in large quantities also encounters considerable difficulties.

In DD-A5-215 803 (EP-A-118 655) an attempt has already been described to achieve a rapid melting and a quick reaction between charge material components in a shaft furnace with the supply of electrical energy by the fact that the upper one between one Covering the shaft furnace penetrating, centrally arranged plasma torch and a counter electrode passing through the bottom of the shaft furnace, a plasma torch is formed, and that the charge material is introduced concentrically around the plasma torch, a protective wall of solid charge material components being piled up on the inner wall of the furnace and the charge material being deposited on the inside Inside the protective wall in the area of the plasma torch.

However, this procedure does not allow the plasma torch to be guided in a targeted manner to melt and / or chemically react the wall formed. Continuous operation of such a shaft furnace is not feasible. The waste gases formed during the reaction must be removed by the Möller, which has further disadvantages this procedure, for example with regard to the condensation of exhaust gas components.

The present invention has now set itself the task of a method and an apparatus for carrying out hot chemical processes, in particular a melt and / or melt reduction of mixtures of metallurgical dusts, ores and other, meltable and / or melt-reducible materials, such as e.g. To provide SiO₂, MgO, TiO₂, Ta₂O₅ or the corresponding metals, with or with which hot-chemical processes can be carried out in temperature ranges that are far above the melting temperature of known refractory bricks. At the same time, hot-chemical-physical reactions should be mastered safely without having to accept a process-technical restriction of the reaction temperatures. Furthermore, as a significant advantage over previously known methods, considerable energy savings and the greatest possible prevention of dust discharge with the exhaust gases are to be achieved.

These objectives are achieved under the procedural aspect of the present invention in that, in a process of the type mentioned at the outset, the mixture to be melted and / or reduced is pressed into blocks with a defined composition, and these are formed around a radiation source having a longitudinal extension, with the formation of a defined cavity geometry high energy density are arranged and the defined cavern geometry is maintained by radially advancing the batch blocks against the centrally arranged radiation source in accordance with the course of the melting and / or melting reduction process.

In the process according to the invention, the batch pressed into blocks thus simultaneously represents the reaction medium and the “lining” of the metallurgical reaction vessel. Depending on the melting rate, the blocks are pressed in such a way that the cavity geometry around the radiation source, for example a plasma torch, remains constant. For this purpose, the batch blocks are advanced radially against the centrally arranged radiation source to the extent that the melting and / or melting reduction process takes place. The plasma torch is held within the cavern by suitable measures, as will be explained in more detail below.

Guide elements are preferably used for the exact supply of the batch blocks to the energy source. The feed material which has been brought into a block form is expediently dried, a certain dimensional stability and cold pressure resistance of the blocks having to be maintained on account of the requirements of the feed system.

When the method according to the invention is applied to the smelting of metallurgical dusts, the procedure can advantageously be as follows, for example from the starting materials shown in the table below:

The feedstocks listed in Table 1 are expediently mixed well with about 9% by weight of water, pressed into blocks of a suitable size and then dried. The dried blocks are arranged radially around a central radiation source with the help of guiding elements which ensure an exact supply of the batch blocks, a cavern with a defined geometry being formed around this radiation source, for example a plasma torch. According to an advantageous embodiment of the invention, the plasma torch can be designed in the manner described in AT-PS 376 702. After igniting the plasma torch emanating from a graphite electrode using argon gas, the argon is used to introduce hydrocarbons and / or finely dispersed graphitin into the plasma torch. The carbon (graphite) is converted into the gas phase by the high plasma temperature and the reduction process is accelerated by ionization of the carbon gas. Furthermore, the burn-up of the graphite electrodes is largely held back by the highly ionized carbon gas atmosphere. After the plasma torch has been ignited between the electrodes, the batch blocks surrounding the plasma torch in a cavernous manner begin to melt. As the blocks melt, they are pushed in from the outside so that the geometry of the caverns remains the same. During the melting process, the hot chemical reaction of a direct reduction takes place at the same time.

Since in the present case this reaction takes place in the absence of air, in addition to argon as the plasma gas at the prevailing high temperatures, only carbon monoxide and hydrogen can be produced as exhaust gases. This gas can be recycled using known technology.

The heavy metal components contained in the feed material evaporate in the process taking place and can for the most part be condensed in a gas exhaust hood or in condenser elements installed in the gas exhaust pipe.

The liquid iron produced in this process can be tapped continuously, and the slag produced is also continuously drained off.

The method according to the invention is also suitable for smelting of sludge resulting from iron ore extraction, for example from the sludge resulting from Erzberg in Styria, Austria. Table 2 below shows the average values of the sludge analysis of iron ore:

As the table above shows, the composition of this sludge already constitutes a self-sufficient Möller. After the addition of carbon according to the stoichiometric requirements, this feed material can be pressed into appropriate blocks and fed to the smelting reduction according to the invention in the process described above. The relevant design and maintenance of the cavern geometry during the entire process is of essential importance for the execution of the method according to the invention.

According to the above principle, all types of metallic ores can be reduced by hot chemical means. In the same way, all melting processes that take place at very high temperatures can be carried out with the method according to the invention. The processing of filter dust and slag residues from incineration plants, such as waste incineration plants, is of particular interest. which can be melted down to such an extent that evaporating heavy metals can be recovered by partial condensation and any remaining trace elements are incorporated into the glass-ceramic end product, from which they can no longer be leached.

A particularly interesting application is the method according to the invention for the direct reduction of bauxite to metallic aluminum. For this purpose, finely ground bauxite is mixed well with carbon in accordance with the stoichiometric requirements and is pressed and dried in the blocks described above and dried in this way and brought to the radiation source that a defined cavern geometry arises and is maintained in the course of the further reactions. After the plasma torch is ignited, the bauxite mixture is melted on the surface, the iron xoid being reduced first and collecting in the collecting vessel to form an iron sump which is saturated with aluminum and enriched with carbon. The aluminum oxide initially occurs as a melt flow (melt mullite) and is mainly converted into aluminum carbide (Al₄C₃) by further energy supply at temperatures> 2,000 ° C according to 2 Al₂O₃ + 9C → Al₄C₃ + 6 CO, from Al³⁺ - and C⁴⁻ ions (heat of formation Δ H = -49.9 kcal / mol). With slow cooling from 1,500 ° C down to about 660 ° C, Al₄C₃ decomposes into metallic aluminum and carbon in the form of graphite, corresponding to Al₄C₃ → 4 Al + 3C. There can also be a reaction of the carbide with Al₂O₃ approximately after the reaction Al₄C₃ + Al₂O₃ → 6Al + 3CO.

In order to achieve a complete conversion of the Al₂O₃ or melting mullite present, the procedure is advantageously as follows:
The initially obtained as a melt flow (melt mullite) Al₂O₃ is driven under the action of the hot gas (CO / H₂ gas) towards a refining vessel, with the formation of aluminum carbide and its subsequent disproportionation. Remaining, unreacted Al₂O₃ melt is in turn returned to the reaction zone in order to achieve complete conversion. In the area of the refining zone, metallic aluminum with a maximum carbon content of 0.05%, a silicon content of about 1%, a titanium content of about 1% and a further contamination with iron of a maximum of 1.8% is tapped. From the below iron, which is saturated with aluminum and enriched with carbon, is continuously drawn off from the reaction basin located in the reaction zone.

As already mentioned at the beginning, the plasma torch is held within the cavern in the method according to the invention. In order to be able to take full advantage of the high energy density of a plasma torch, it would be necessary to guide the plasma torch exactly within the defined cavern. Furthermore, to optimize the melting and reduction process, it would be essential to adhere as precisely as possible to the energy required, i.e. the enthalpy of fusion and the enthalpy of reduction, to carry out the hot-chemical processes, and to optimally adapt the gasification enthalpy of the graphite in the plasma torch to the total energy supplied to the plasma torch . This task can only be solved unsatisfactorily with conventional plasma torch technology. This conventional technology provides that a plasma torch is built up between two electrodes, a top and a bottom electrode, and / or between a top and two or three side electrodes. The plasma torch can burn out a cavern on one side within the furnace, since it cannot be guided in a controlled manner.

A further advantageous embodiment of the method according to the invention now makes it possible to achieve the above-mentioned task of precisely maintaining the energy input and controlled guidance of the plasma torch within the defined cavern by the fact that between the main electrode, the head electrode, which extends into the cavern, and a number of Radial electrodes (a to h), which are arranged directly under the cavern, the plasma torch is ignited. The radial electrodes are charged with a base load for ionizing the gas atmosphere by means of thyristor control, while the main load is distributed over the thyristors via thermocouples, which are attached to the front edge of the control system, in such a way that the uniform melting rate within the cavern surface is ensured.

A further, advantageous embodiment provides that the melted material which is collected in the collecting vessel, via a bottom electrode arranged in the collecting vessel, which is controlled via a bath temperature measurement, can also get an energy input from the radial electrodes so that the bath temperature can be kept constant.

According to a further aspect, the present invention relates to a device for carrying out the method described at the outset with a centrally arranged cavity of defined geometry formed by blocks of meltable and / or melt-reducing batch, radially arranged guide elements for feeding the batch blocks to the center, one below arranged in the cavern, with vents for the molten metal and the liquid slag, a central electrode arrangement, a cover arranged above the cavern, a gas exhaust hood and a gas exhaust pipe.

Exemplary embodiments of the device according to the invention are shown in the accompanying drawings. 1 shows a cross section through an embodiment of the device according to the invention, while FIG. 2 shows a top view of this device. 3 and 4 represent a cross section or a top view of a further device according to the invention which is particularly suitable for the direct reduction of bauxite. In FIG. 5 a further embodiment of the device according to the invention is shown in a schematic diagram, with which embodiment the Energy input exactly adhered to and the plasma torch can be guided within the defined cavern in a controlled manner.

In these drawings, the cavern 1 is formed by the mixture to be melted and / or melt-reducing, which is supplied in the form of pressed blocks 11 from the outside radially inwards. The radially arranged guide elements 2 ensure an exact feed of the batch blocks to the center. In the receptacle 3 under the cavern 1 there are the fume cupboards for the molten metal and for the liquid slag at suitable points. 4 denotes the upper electrode, the lower electrode 10 is arranged on the bottom of the collecting vessel 3. 5 represents the top cover of the reaction vessel, 6 and 7 are the exhaust hood and the exhaust pipe, respectively. 8 and 9 each designate a connecting channel which leads from the collecting vessel 3 to another collecting vessel (3 '), FIG. 1, 2, serving as a refining vessel, or to two such collecting vessels (3', 3 "), FIG. 4, which are also connected to one another by a channel (9). In FIG upper or head electrode 4 on the required power and gas supply and can be moved with a carriage or the like in the vertical direction. Immediately below the cavern 1, a number of radial electrodes (a to h) are arranged in a horizontal plane, which can be moved forwards and backwards in the radial direction and are preferably rotatable about the respective radius. A bottom electrode 10 can be provided in the collecting vessel below the cavern 1.

By carrying out the method according to the invention, it is possible to convert the oxidic components of the mixture directly into a melt flow and to carry out the reduction to metals from the liquid phase. The advantage of this technology over the conventional method is that e.g. the Fe₂O₃ can be reduced to Fe not only via the detour via Fe₃O₄ and FeO, but directly via the melt flow Fe₂O₃ to Fe, whereby the presence of a favorable mixture gap can be exploited where iron in pure form without contamination by carbon, silicon, manganese, Phosphorus etc. is obtained and is in equilibrium with liquid Fe₂O₃, see ULLMANN'S ENCYCLOPEDIA OF TECHNICAL CHEMISTRY, 4th edition, volume 10, page 334.

Claims (9)

1. Method for carrying out hot-chemical processes on mixtures comprising foundry dusts, ores and other melting and/or melt-reducible materials at working temperatures which exceed the melting temperature of highly refractory linings, characterized in that the mixture which is to be melted and/or reduced and which is of defined composition, is pressed into bars and these are arranged, to form a defined cavern geometry, around a longitudinally extending source of radiation of high energy density, and the defined cavern geometry is maintained by radially advancing the bars of the mixture toward the centrally-arranged source of radiation according to the progress of the melting and/or melting-reduction process.
2. Method according to claim 1, characterized in that a plasma jet is used as the source of radiation of high energy density.
3. Method according to claim 2, characterized in that, after the ignition by means of argon gas of a plasma jet, which originates from a graphite electrode, hydrocarbons and/or finely dispersed graphite is/are introduced with this gas into the plasma jet.
4. Method according to any one of claims 1 to 3, characterized in that guide elements are arranged for the precise advancing of the mixture bars.
5. Method according to any one of claims 1 to 4, characterized in that SiO₂, MgO, TiO₂, Ta₂O₅ or Al₂O₃ or the corresponding metals are subjected to a melting reduction process or melting process.
6. Method according to any one of claims 1 to 5, characterized in that a plasma jet is erected between a top electrode, which projects into the cavern, and a plurality of radial electrodes, which are arranged immediately below the cavern, and these are loaded with a basic load for the ionization of the gas atmosphere, while the main load is distributed to the radial electrodes in such a way that a uniform melting rate within the cavern surface area is ensured.
7. Method according to claim 6, characterized in that, additionally, a bottom electrode, which is arranged in the collecting basin for the melting stock, for the stabilization of the bath temperature is supplied with an energy input by the radial electrodes.
8. Apparatus to carry out the method according to any one of claims 1 to 7, comprising a geometrically-defined cavern (1) formed by bars of melting and/or melt-reducible mixture, radially-arranged guide elements (2) for advancing the bars of mixture towards the centre, a collecting basin (3) which is arranged below the cavern (1) and which is provided with outlets for the metal melt and the liquid slag, a central electrode arrangement (4), a covering (5) arranged above the cavern (1), a gas hood (6) and a gas-vent pipe (7).
9. Apparatus according to claim 8, characterized by at least one additional collecting basin (3') serving as clarification zone, which basin is in communication with the collecting basin (3) below the cavern (1) or with other collecting basins (3") via connecting passages (8, 9).

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