RU61283U1 - PLASMA ARC FURNACE - Google Patents

Abstract

The essence of the utility model lies in the fact that in a plasma-arc furnace, including mechanical means for supplying the charge, means for creating an arc and a crucible with a melt, the walls or / and the bottom of the crucible are provided with openings located below the level of the mirror of the bath, with which the means of supplying the charge are docked. This allows the charge to be introduced into the melt by feeding the mixture below the melt bath mirror onto the side and / or lower surface of the melt in the form of a stream of condensed phases without using a transport gas. Moreover, the interface between the unmelted charge and the melt partially or completely limits the melt and forms the walls of the crucible. The proposed utility model solves two technical problems: a more complete use of the supplied raw materials and reduction of energy losses from the melt pool. The main technical result of using the proposed utility model is to exclude the entrainment of the dispersed charge with exhaust gases from the furnace due to the fact that at the stage of introducing the dispersed charge its contact with any gases supplied to or removed from the furnace is excluded. Additionally, the task of reducing the consumption of the electrode is solved.

Description

The utility model relates to non-coke metallurgy, in particular, to devices for direct reduction of iron group metals from dispersed oxide raw materials by gaseous and dispersed reducing agents.

Known plasma-arc furnace with a molten bath for metal recovery (Tsvetkov Yu.V., Panfilov SA "Low-temperature plasma in the recovery process", M., Nauka, 1980, p.232). The furnace has a ceramic crucible and a plasmatron introduced into the working space of the furnace through its arch. The plasma arc burns directly on the melt located in the ceramic crucible. The melt acts as an anode; current is supplied to it through a hearth electrode. The charge is introduced from above onto the bath mirror. In the case of metal reduction, a plasma-forming gas, which is a necessary chemical reagent, is supplied to the furnace, while the recovery process is accompanied by a large amount of both the supplied to the furnace and the exhaust gas discharged through an opening in the roof.

The furnace has the following disadvantages:

1. With the exhaust gases, a significant part of the feed mixture is carried away.

2. Crucible ceramics chemically interacts with the melt, polluting it.

3. The use of ceramic crucibles in the reduction of metal oxides requires frequent shutdown of the process to replace or repair the crucible due to the high erosion of ceramics during the smelting process.

To eliminate the first drawback, cyclone reactors are used (Dust utilization from steelmaking in electric arc furnaces, L.N. Kuznetsov, L.A. Volokhonsky, Electrometallurgy No. 9, 2004) or devices for introducing dispersed reagents into the melt by means of a gas jet (US Pat. RF No. 2226219)

The listed charge input devices do not radically solve the problems of material entrainment with exhaust gases. So, the use of various designs of cyclone apparatus complicates the technological scheme and leads to significant energy costs, since these devices are based on gas thermal enlargement of the dispersed mass (fusion, coagulation, particle sticking). The ablation of material from the reactor reaches 20% and higher.

In the patent of the Russian Federation No. 2226219, the crucible walls at a level above the melt bath are provided with holes with tuyeres inclinedly inserted into them, the lower ends of which are lowered into the melt. The mixture is introduced into the melt using high-speed gas jets through cooled tuyeres immersed in the melt bath. This leads to large additional energy costs as a result of cooling the melt by the transporting gas. In addition, a high-velocity gas jet introduced into the melt facilitates the discharge of the dispersed charge and droplets of the melt into the region above the melt and, ultimately, entrainment of the processed material with exhaust gases.

In a well-known plasma-arc installation (US Pat. RF No. 2072639 from 1992), the finely dispersed part of the charge carried away by the exhaust gas is collected using a separately installed dust precipitation chamber, in the outlet pipe of which a fine filter is equipped, equipped with filter elements from composite heat-resistant materials, the charge is fed through an opening in the lid, and the walls and bottom of the reactor chamber are protected by ceramic lining. The use of filters made of composite materials complicates and increases the cost of the design, and the presence of ceramic reactor protection has the same disadvantages as in other known devices.

To eliminate the second and third drawbacks, metal cooled crucibles are used (“Industrial Electric Furnaces. Arc Furnaces and Special Heating Units.” Edited by Svenchansky AD, M., Energoizdat, 1981). In this case, however, the heat loss through the crucible wall increases substantially.

The closest prototype of the proposed device is a plasma-arc furnace, including means for feeding the charge, means for creating an arc and a crucible with a molten bath (Plasma-arc reduction furnaces in the structure of the energy metallurgical complex, A.V. Nikolayev, A.A. Nikolayev, Proceedings of the Fifth Congress of Steelmakers . 1999). The molten bath is formed in a cooled copper crucible connected to one of the poles of the power source. The plasma arc burns between the surface of the bath and a hollow graphite electrode introduced through the arch of the furnace and connected to the other pole of the power source. The charge is introduced into the furnace through an axial channel in the electrode. In this case, the charge is fed to the surface of the bath in the area of the electrical arc binding.

In this device, the mixture leaving the channel of the electrode above the surface of the bath falls into the zone of high-speed gas flows. Moreover, a significant part of the introduced charge does not reach the surface of the bath and is carried away from the furnace with waste

gases. In addition, a mixture consisting mainly of metal oxides, passing through a channel of a graphite electrode, chemically interacts with graphite and causes erosion of the electrode. Chemical interaction is endothermic and is accompanied by a decrease in the temperature of the electrode, which violates the stability of the plasma arc.

The use of a cooled copper crucible in this device made it possible to improve the quality of the melted metal, however, the heat losses from the molten bath to the crucible walls increased significantly.

The essence of the utility model is that the charge is introduced into the melt by feeding the mixture below the melt bath mirror to the side or / and lower surface of the melt in the form of a stream of condensed phases without the use of a transport gas. Moreover, the interface between the unmelted charge and the melt partially or completely limits the melt and forms the walls of the crucible.

The proposed utility model solves two technical problems: a more complete use of the supplied raw materials and reduction of energy losses from the melt pool.

The main technical result of using the proposed utility model is to exclude the entrainment of the dispersed charge with exhaust gases from the furnace due to the fact that at the stage of introducing the dispersed charge its contact with any gases supplied to or removed from the furnace is excluded. Additionally, the task of reducing the consumption of the electrode is solved.

This result is achieved by the fact that in a plasma-arc furnace, including the charge supply means, the means for creating an arc and the crucible with the melt, the walls or / and the bottom of the crucible are provided with openings located below the level of the mirror of the bath, with which the mechanical means of supply of the charge are docked.

The introduction of the charge into the melt can be carried out in radial and axial versions. In a radial design, the charge inlet openings are located in the side walls of the crucible, and in the axial design, the input openings are not necessarily coaxial in the bottom of the crucible along its axis.

Terms and definitions used

Plasma arc - an electric arc burning in the gas supplied to the discharge gap.

Plasma-arc furnace - a device containing one or more electrodes for forming a plasma arc and a crucible with a processed material, heating,

melting and chemical-thermal treatment of which is carried out using a plasma arc.

Oxide raw materials - ores, concentrates and industrial substances based on metal oxides.

A mixture is a mixture consisting of oxide raw materials, alloying and refining additives and, in some cases, a solid reducing agent.

Condensed phase - a substance in a solid or liquid (but not gaseous) state.

Description of the drawings.

Figure 1 schematically in longitudinal section presents a plasma-arc furnace with a radial input of the mixture into the melt.

Figure 2 schematically in longitudinal section shows a furnace with an axial introduction of the mixture into the melt.

Figure 3-4 shows the options for crucibles in cross section with radial inputs of the mixture into the melt.

Figure 5 shows a variant of the crucible in cross section with radial and axial inputs of the charge into the melt.

The device shown in Fig. 1 comprises a water-cooled copper crucible 1 with a side opening 2 for introducing a charge 3 and a bottom opening 4 with a locking device 5 for releasing a melt 6, a source of reducing gas 7 with a pipe 8, a hopper 9 with a charge, mechanical (for example , auger) charge supply means 10, vault 11 with a hole 12 for exhaust gas, a graphite electrode 13. Electricity is supplied to the crucible 1 and electrode 13 through terminals 14 and 15, the plasma arc 16 burns between the melt 6 and electrode 13.

In the device shown in figure 2, the hole 2 for introducing the mixture into the melt 6 and the means for feeding the mixture 10 are placed in the bottom of the crucible on the vertical axis of the furnace or in alignment with it. The hole 4 for draining the melt is placed in the crucible 1 on the side.

Implementation of a utility model.

The operation of the device when the charge is radially introduced into the melt is illustrated (Fig. 1). In the crucible 1, a metal “seed” is loaded in the form of an agglomerated material of such a mass that, when it is melted, the melt level 6 is higher than the holes 2. Using the locking device 5, close the hole 4, apply voltage to the electrode 13 and the crucible 1 through terminals 14 and 15, a plasma-forming gas is supplied (to the channel of the electrode 13, if it is hollow), a plasma arc 16 is excited between the electrode 13 and the “seed” 16 using one of the known methods,

for example, by briefly touching the “seed" with the electrode, spark discharge, etc. and melt the "seed". After that, in the hole 2 serves the mixture 3 and melt it. A mixture consisting only of condensed phases is introduced by mechanical means 10 without using a transport gas into the melt bath below the level of the bath mirror through one or more openings 2 located in the crucible walls so that the melting front of the fed mixture is in a stationary state, i.e. . the charge 3 is supplied at such a speed that inside the crucible 1 in the vicinity of the holes 2 a stationary interface forms between the solid charge and the melt and the interface between the melt and the solid charge completely or partially limits the melt and serves as the wall of the crucible.

The area of this surface is at least equal to the area of the holes 2. Thus, the contact surface of the melt 6 with the cooled crucible 1 is reduced by at least the size of this area, which leads to a decrease in heat loss through the wall of the crucible. To prevent the increase in the level of the melt 6 above the permissible periodically or constantly by a predetermined amount, open the hole 4 and release the molten metal.

The operation of the device with the axial introduction of the charge into the melt (figure 2) occurs in a similar way. Metal is produced through hole 4 in the side wall of the crucible.

The proposed design allows to reduce the fraction of heat entering from the melt into the walls of the crucible, which is lost with cooling water and creating problems with cooling in many cases, and to increase the fraction of heat useful for heating and melting the incoming charge acting as a “sacrificial wall”, which significantly reduces energy costs for metal production. The introduction of the charge below the bath mirror prevents contact of the charge with the streams of the incoming and exhaust gases and, as a result, the entrainment of small fractions of the mixture with the exhaust gases while guaranteeing complete melting of the incoming shield.

With the elimination of the contact of the charge with the working electrode, one of the main causes of its erosion is eliminated.

Thus, the present invention allows:

- to eliminate the loss of the charge due to the ablation of part of it with the exhaust gases;

- reduce the energy intensity of the process by reducing the heat transfer surface of the melt with the cooled metal crucible as a result of partial or complete replacement of this surface by the melting surface of the mixture;

- improve the environmental performance of the furnace by reducing dust emissions in

atmosphere;

- reduce the consumption of graphite electrode due to the exclusion of its contact with oxide raw materials.

The invention can be used at the enterprises of metallurgy and mechanical engineering for the direct production of metal in the form of castings, metal powders and granules from dispersed oxide raw materials using gaseous and dispersed reducing agents.

The energy and environmental indicators of the proposed method of introducing the charge into the plasma-arc furnace is significantly higher than that of the analogues: it does not require agglomeration of fine oxide raw materials, gas is not used to transport the charge.

The possibility of realizing all the effects that accompany the use of the proposed device for introducing a charge into a plasma-arc furnace was first established by us and has not been published anywhere.

Claims (1)

Plasma-arc furnace, including means for supplying a charge, means for creating an arc and a crucible with a melt, characterized in that the walls and / or bottom of the crucible are provided with openings located below the level of the mirror of the bath, with which the mechanical means of supplying the charge are docked.