RU2335549C2 - Method of plasma arc furnace charging and device for implementation of method - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: in plasma arc furnace agglomerate is preliminary melted for direct reduction of metal, then charging is carried out immediately into melt below level of metal heel with screw conveyer of charge feed; then melting of charge in crucible is performed followed by melt tapping. Charge is fed onto side/side and bottom surface of melt through holes at amount of not less, than two on the side surface at a rate facilitating forming of stationary surface of division between a solid charge and the melt, completely or partially limiting the melt and functioning as a crucible wall.

EFFECT: invention facilitates avoiding disperse charge loss with exhaust gases.

2 cl, 5 dwg

Description

Technical field

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

State of the art

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, which is subject to severe erosion during the melting process. 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 gas and the exhaust gas discharged through an opening in the roof. With the exhaust gases, a significant part of the feed mixture is carried away.

To reduce the entrainment of the charge, various methods of introducing the charge are used: compacting and pelletizing oxide fines (Kinetics of recovery and morphological evaluation of self-healing briquettes based on hematite and magnetite ores, J.Kh. Noldin et al., Steel No. 10, 2005), the use of cyclone reactors (Dust utilization from steel production in electric arc furnaces, L.N. Kuznetsov, L.A. Volokhonsky, Electrometallurgy No. 9, 2004), the supply of oxide fines directly into the arc discharge of the furnace through the internal cavity of the plasma electrode otron (Plasma-arc reduction furnaces in the structure of the energy and metallurgical complex, A.V. Nikolayev, A.A. Nikolayev, Proceedings of the Fifth Steelmakers Congress, Moscow, 1999), introduction of dispersed reagents into the melt by means of a gas jet (Application of injection technologies in electric melting ferrous metals, V.G. Dyubanov et al., Proceedings of the Fourth Steelmakers Congress, Moscow 1997, Pat. RF No. 2226219).

The above methods and devices for introducing the charge do not radically solve the problem of entrainment of material with exhaust gases. So, compacting and pelletizing dispersed materials is a complex and energy-intensive technological process. The use of various designs of cyclone devices also significantly complicates the technological scheme and also leads to significant energy costs, since these devices are based on gas thermal enlargement of the dispersed mass (melting, coagulation, particle sticking). The ablation of material from the reactor in all these methods is also significant - up to 20% and above. In addition, the supply of dispersed materials through the cavity of the electrode leads to a significant increase in the consumption of the electrode due to its chemical interaction with the oxide.

In the well-known plasma-arc installation (US Pat. RF No. 2072639 from 1992), the finely dispersed part of the charge carried out by the exhaust gas is collected using a separately installed dust precipitation chamber, in the outlet pipe of which a fine filter is equipped with filtering elements made of composite heat-resistant materials, while 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 prevent erosion of ceramics, metal water-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 method is a method of introducing a charge into a plasma-arc furnace, including preliminary melting of the agglomerated material in the furnace, introducing the charge directly into the melt below the level of the bath mirror, melting the charge in the crucible, and releasing the melt (US Pat. RF No. 2226219). According to this method, the mixture is introduced into the melt by means of high-speed gas jets through cooled molds installed in the side walls of the crucible and immersed in the molten bath. This leads to large additional energy costs as a result of the cooling of the melt by the transporting gas and, in addition, the high-velocity gas jet introduced into the melt contributes to the discharge of the dispersed charge and drops of the melt into the region above the melt and ultimately to the removal of the processed material with exhaust gases.

The closest prototype of the proposed device is a plasma-arc furnace for direct reduction of metals, including means for feeding the charge, means for creating an arc and a crucible with a molten bath (RU No. 2040548). A plasma-arc furnace is a fragment of a two-zone material processing reactor containing a melting chamber with plasmatrons, a dust-filled material hopper connected to the melting chamber through a hole in the side wall of the chamber, and a sealed charge metering hopper. The pulverized material is periodically fed through the reciprocating mechanism into the melting chamber, into the melt of the charge fed from the metering hopper to reduce dust entrainment and increase the utilization rate of pulverized materials. In this device, the charge exiting from the metering hopper above the bath surface enters the zone of high-speed gas flows. In this case, a significant part of the introduced charge does not reach the surface of the bath and is carried away from the furnace with exhaust gases. A large proportion of the energy input is lost through the walls of the crucible.

The present invention solves two technical problems: a more complete use of the supplied raw materials and reducing energy losses from the molten bath.

The main technical result of the use of the invention is to eliminate the entrainment of the dispersed charge from the furnace with the exhaust gases due to the fact that the contact of the dispersed charge with the jet streams of any gases supplied to or removed from the furnace is excluded.

This result is achieved by the fact that in the method of introducing the charge into the plasma-arc furnace for direct reduction of metals, including preliminary melting of the agglomerated material in the furnace, introducing the charge directly into the melt below the level of the bath mirror, melting the charge in the crucible and releasing the melt, the charge is introduced to the side or / the side and bottom surface of the melt, and the charge is supplied at a speed that ensures the formation of a stationary interface between the solid charge and the melt, this surface is completely or partially limits the melt and acts as a crucible wall.

Another aspect of the invention is that in a plasma-arc furnace for direct reduction of metals, including charge feeding means, arc generating means and a crucible with a melt, the side wall of which is provided with an opening, the walls / walls and the bottom of the crucible are provided with openings in an amount of not less than two on the walls located below the level of the bath mirror, with which the screw means for feeding the charge are docked.

The charge is introduced into the melt by mechanically feeding the charge below the melt bath mirror onto the side / side and bottom surface of the melt using a screw mechanism without using transporting gas. The interface between the unmelted charge and the melt partially or completely limits the melt and forms the walls of the container for the melt.

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, the 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.

Description of the drawings.

Figure 1 schematically in longitudinal section shows a plasma-arc furnace with one for clarity of the drawing by radial introduction 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 several radial inputs of the charge 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 figure 1, contains as an example a copper water-cooled 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 7 of reducing gas with a pipe 8, a hopper 9 with a charge, screw feed means for charge 10, vault 11 with a hole 12 for exhaust gas, graphite electrode 13. Power 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. The number of holes 2 should be not less than two on opposite walls of the crucible.

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.

The implementation of the invention

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” electrode, spark discharge, etc. and melt the "seed". After that, in the hole 2 serves the mixture 3 and melt it. The mixture with a screw mechanism without using transporting gas is introduced into the molten bath below the level of the bath mirror through two or more openings 2 located in the crucible walls so that the melting front of the fed mixture is mainly in a stationary state, i.e., the mixture 3 is fed at such a speed so that inside the crucible 1 in the vicinity of the holes 2 a predominantly stationary interface is formed between the solid charge and the melt and this surface completely or partially limits It melt and acted as a crucible wall. 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 an opening 4 in the side wall of the crucible 1.

Figure 3, 4 presents variants of the invention for different (non-circular) cross sections of the crucible 1 - triangular (figure 3) and hexagon (figure 4). In each face of the crucible 1, holes 2 are made, with which the mechanical means of supplying the charge are docked 10. The hole 4 for the release of metal is placed in the bottom of the crucible.

The interface surface area is at least equal to the area of the holes 2. Therefore, the contact surface of the melt 6 with the cooled crucible 1 is reduced by the value of this surface, which leads to a decrease in heat loss through the wall of the crucible. In practice, the charge entering the crucible does not remain strictly opposite the holes 2, but spreads in all directions, therefore, for small sizes of the crucible, two holes 2 on opposite walls of the crucible are enough to form a heat-insulating surface that separates a significant part of the surface of the crucible walls from the melt. The same effect occurs with the bottom arrangement of holes 2 (Fig.2, 5).

In Fig. 5, crucible 1 with a circular cross-section for example is provided with both side and bottom openings 2 for supplying charge 3. The charge 3 fed through openings 2 forms a heat-insulating layer between the melt and the crucible, wherein the number of openings 2 and the feed rate of the charge are selected from conditions for the absence of significant gaps in the heat-insulating layer created by the incoming charge.

The present invention allows to reduce the fraction of heat entering from the melt into the crucible walls and lost with cooling water, creating in many cases problems with cooling, 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 mechanical input of the charge by means of a screw mechanism below the bath mirror prevents the charge from contacting the streams of incoming and outgoing gases and, as a result, the entrainment of small fractions of the charge with the exhaust gases while guaranteeing complete melting of the incoming charge.

Thus, the present invention allows:

- to eliminate the loss of the mixture due to entrainment with 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;

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 method of introducing a charge into a plasma-arc furnace proposed in the present invention was established by us for the first time and has not been published anywhere.

Claims (2)

1. The method of introducing a charge into a plasma-arc furnace for direct reduction of metals, in which preliminary the melted material is carried out in the furnace, the charge is fed directly into the melt below the level of the bath mirror, the charge is melted in the crucible, and the melt is released, characterized in that the charge is fed to the side / side and bottom surfaces of the melt at a speed that ensures the formation of a stationary interface between the solid charge and the melt, completely or partially restricting the melt and acting as walls and crucible. 2. Plasma-arc furnace for direct reduction of metals, including means for supplying a charge, means for creating an arc and a crucible with a melt, characterized in that the walls / walls and the bottom of the crucible are made with holes with which the screw means for feeding the charge are connected, the holes being located below level of the bath mirror in an amount of at least two on the side surface.

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