RU2007676C1 - Plasma furnace - Google Patents

Abstract

FIELD: plasma engineering. SUBSTANCE: plasma furnace comprising lined bath and roof with holes for the passage of plasma generators is characterized in that the plasma generators are made in the form of at least two telescoping graphite tubes with high-melting insulating coating on the surface. Pipes are installed in a spaced relation to each other for the flow of plasma-generating gas. EFFECT: improved design. 2 dwg

Description

 The invention relates to metallurgical plasma and arc furnaces in which an electric arc is used to heat and melt the charge. In particular, the arc was used to form a gas plasma that carries out heating.

 Known arc metallurgical electric furnaces containing a lined tank, consisting of a bath for melting metal, walls and a vault, through which graphite electrodes are introduced into the lined tank in the form of rods capable of independent vertical movement. Heating and melting of the charge is carried out by an electric arc burning between a conductive charge and electrodes.

 The disadvantages of the arc furnace is poor heat transfer from the electric arc to the metal in the bath, since the heating is largely localized in the arc burning area, which is small compared to the size of the furnace bath.

 An additional disadvantage of the arc furnace is the strong noise arising from the burning of the arc, which has a harmful effect on the staff serving the furnace.

 The second additional disadvantage of the arc furnace is the emission of gases from the working space of the furnace into the workshop room, which pollutes the workshop and the surrounding space. The emission of gases occurs mainly through the gap between the electrodes and the lining of the roof of the furnace, through the holes into which the electrodes are introduced.

 Also known is a plasma furnace adopted for the prototype, containing a lined tank, consisting of a bath for melting metal (crucible), the walls of the lined tank and a vault through which plasmatrons are introduced into the lined tank. The disadvantage of these furnaces is the short life of the plasmatrons (several hundred hours), due to the rapid destruction of the electrodes of the plasma torches under the influence of an arc discharge.

 An additional disadvantage of plasma furnaces is the need to use expensive and scarce tungsten alloys for plasma torch cathodes.

 The second additional drawback of plasma furnaces is the operation of direct current plasmatrons, which requires the use of powerful rectifiers in the power system, which significantly complicates the equipment.

 The third additional drawback of plasma furnaces is the difficulty in obtaining plasma of oxidizing gas (oxygen, air), which is necessary to ensure carbon burnout if a lot of pig iron is loaded into the initial charge.

 Due to these shortcomings, plasma furnaces are not widely used in metallurgy.

 The aim of the present invention is to increase the efficiency of plasma furnaces by eliminating the above disadvantages, using plasmatrons of a special design.

 This goal is achieved due to the fact that the plasma furnace contains a lined bath and a vault with openings for the passage of plasmatrons and differs in that the plasma torches are made in the form of at least two graphite tubes coaxially inserted into one another with a refractory insulating coating on their surface, and the pipes are installed one into another with a gap for the passage of a plasma-forming gas.

 The essence of the invention lies in the fact that graphite tubes with a refractory insulating coating coaxially inserted one into another form plasmatrons that do not contain expensive and scarce tungsten alloys. An arc or several arcs burning at the ends of pipes, as well as in arc metallurgical furnaces (1), can be maintained during operation on both alternating and direct currents. In this case, one or several different plasma-forming gases, including air or oxygen, can simultaneously be passed through the gaps between the tubular electrodes.

 In FIG. 1 shows a diagram of a furnace device, a longitudinal section; in FIG. 2 is a diagram of a device and an arrangement of tubular graphite electrodes forming a plasmatron, a longitudinal section.

 The furnace consists of a bath 1, in which a layer of molten metal 2 is formed, covered with a layer of slag 3. The bath is covered with a vault 4 resting on the walls 5. Plasmatrons 6 formed by tubular graphite electrodes are introduced into the furnace through the vault. To prevent the emission of gases from the furnace into the surrounding space around the plasmatrons 6, seals 7 are made of fibrous material, for example carbon fiber. Gas or several gases are simultaneously supplied to the plasma torches 6 through pipes 8. Like graphite electrodes in arc furnaces (1), the plasma torches 6 are equipped with devices for their independent vertical movement. For removal of exhaust gases, pipes 9 are used, connected to a dust cleaning gas system and a waste gas heat recovery system (for example, for household needs).

 For loading the charge, filling windows are the same as in open-hearth furnaces.

 The plasma torch (Fig. 2) consists of two graphite tubes 10 and 11 coaxially inserted into one another, coatings from the inner and outer surfaces with a thin layer 12 of refractory insulating material (for example, a layer of fine aluminum oxide 0.5-1.0 mm thick). Between the pipes there is a gap 13 for passing a plasma-forming gas. To align the pipes relative to each other, refractory insulating gaskets 14 (for example, of ceramic based on alumina) are used in the form of rings in which holes 15 are made around the circumference for transmitting plasma-forming gas. To expand the functionality of the plasma torch through the inner hole 16 of the pipe 11 can also be supplied with gas, or the same as in the gap 13, or another. Metal current leads 17 and 18 are tightly mounted on the pipes 10 and 11. The inner surface of the current lead 17 and the outer surface of the current lead 18 are coated with an electrical insulation layer 19. FIG. 2, this insulation is shown only on the current lead 18. This insulation is already sufficient for reliable operation of the plasma torch.

 Conductors 20 and 21 are used to supply voltage or direct current. The pipes 22 and 23 are used to introduce gases into the plasma torch. In this case, the pipe 23 passes through an electrically insulating seal 24. Gas enters the pipes 22 and 23 through pipes 8 from gas injection devices.

 In FIG. 2 shows the simplest construction of a plasma torch formed by two coaxially inserted graphite tubes. However, to increase the power of the plasma torch, it can be made in the form of several coaxially inserted one into the other with a gap of graphite tubular electrodes, in the gap between which several different plasma-forming gases or the same gas flows. At the ends of the pipes, several electric arcs burn. In particular, in this way from 6 pipes it is possible to create a plasmatron operating on a three-phase alternating current.

 Since the surface of the tubular electrodes is coated with a layer of refractory electrical insulation that is inert with respect to gases flowing in the gaps between the pipes, oxidizing (air, oxygen), inert (argon, nitrogen) or reducing (e.g. hydrogen) gases can be passed through the plasma torch, which is essential expands the capabilities of the claimed furnace.

 The design of the plasma furnace (Fig. 1) is similar to the design of the open-hearth furnace. As in open-hearth furnaces, the charge is loaded through filling windows. After loading the charge, the windows are closed and gas or gases are supplied through pipes 8, plasmatrons 6 are ignited, and the charge is heated and melted, as in previously known plasma furnaces adopted as a prototype. Ignition of the plasma torches is carried out either by short-term contact of the ends of the tubular electrodes of the plasma torch with a conductive charge, as in arc furnaces (1), or by briefly supplying high voltage and high frequency, as is done when igniting the arc in high-pressure discharge lamps. To obtain high voltage with high frequency, you can use the widespread Tesla transformer.

 Depending on the composition of the charge being loaded, the composition of the gas blown into the plasma torches can be different. Accordingly, the method of operation of the furnace may change.

 The simplest option for the furnace is to load the bath 1 with molten iron with the addition of scrap metal, as when loading converters. In this case, the plasma-forming argon gas is blown through the plasma torches 6 through the gap 13 (Fig. 2), and air or oxygen is supplied through the internal channel 16 of the pipe 11. It is possible that air or oxygen can also be used as a plasma-forming gas. The gas (or gases) entering the furnace at a high speed breaks through the slag layer 3 (Fig. 1) and the oxygen interacts with the molten metal, as in converters with an overflow, resulting in carbon burnout from cast iron and steel. Since the gas coming from the plasma torches is very hot, the proportion of scrap used in smelting can be much larger than in converters.

 If scrap metal with slag additives is used as a charge, then one or more inert gases (for example, argon, nitrogen) are blown through plasmatrons 6. All other smelting operations are the same as in the case of loading cast iron with scrap. The acceleration of steel smelting in this case is achieved due to the rapid heating of the charge and therefore, that there is no need to carry out the decarburization of the melt.

 The proposed plasma furnace allows to obtain metal, in particular steel, directly from ore oxides subjected to preliminary enrichment. In this case, the enriched ore with slag-forming additives is loaded into the furnace, and argon is passed through the gap 13 (Fig. 2) as a plasma-forming gas, and reducing gas (for example, hydrogen) is passed through the channel 16. The metal is recovered from the ore and melted, and the waste rock goes to slag. In this version of the work, the process of producing cast iron for the production of steel or iron pellets with direct reduction of ore with the aim of their subsequent remelting in arc furnaces to produce high quality steel is eliminated.

 In all versions of a plasma furnace, metal is released, as in open-hearth furnaces, through an outlet.

 In all versions of the plasma furnace, the resulting steel is subjected to after-furnace treatment to improve quality.

 Using plasmatrons (Fig. 2), the electric arc furnaces for steelmaking (1) can easily be converted into the plasma furnace depicted in FIG. 1. For this, together with conventional carbon electrodes, the plasmatrons shown in FIG. 2, and provide for a gas exhaust system through pipes similar to pipes 9 in FIG. 1. At the same time, arc furnaces will be transformed into high-performance, modern, plasma-free non-noise and non-polluting plasma furnaces for the production of high-quality steel and special alloys.

 An important advantage of the plasma furnaces of FIG. 1, it is possible to carry out the reconstruction of open-hearth furnaces without large capital expenditures and turn them into high-performance plasma furnaces. To do this, through the arch of open-hearth furnaces, the plasmatrons depicted in FIG. 2 and arrange them as shown in FIG. 1. At the same time, the quality of steel will improve due to the removal of the main sources of sulfur during open-hearth melting - fuel burned in open-hearth furnaces.

 In the CIS countries, about 60% of all steel is smelted in open-hearth furnaces. Therefore, the reconstruction of open-hearth furnaces in order to increase their productivity and improve the quality of steel is one of the most important tasks of metallurgy. The proposed plasma furnace solves this problem.

 The economic effect of using the new plasma furnace is very large, but it is currently difficult to quantify it. (56) Voskoboinikov V.G. et al. General metallurgy. M., Metallurgy, 1985, p. 284.

Claims (1)

 A PLASMA FURNACE containing a lined bath and a vault with openings for the passage of plasmatrons, characterized in that the plasmatrons are made in the form of at least two graphite tubes coaxially inserted into one another with a refractory insulating coating on their surface, the pipes being installed one into the other with a gap for passage of plasma-forming gas.

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