RU2315813C1 - Plasma furnace used for the direct reduction of the metals - Google Patents

Abstract

FIELD: cokingless metallurgy; other industries; methods of production of the blanks by reduction of the metals oxides out of the metal-containing oxide raw in the plasma-chemical reactors.

SUBSTANCE: the invention is pertaining to the field of the coke metallurgy, in particular, to production of the blanks by reduction of the metals oxides out of the metal-containing oxide raw in the plasma-chemical reactors. In the plasma furnace the electrodes are the hollow cathode mounted on the central axis with the capability of movement, and the anode associated with the device of collection, and the magnetic field in the volume of the process chamber is formed by the magnetic system. The furnace is supplied with the means of feeding of the SHF-energy in the process chamber. The fusion mixture input device is made in the form of the being cooled internal electroconductive pipe located in the cathode cavity with a spacing and isolated from it electrically. The device of feeding of the SHF energy is made in the form of the coaxially- waveguide adaptor consisting of the rectangular waveguide, which axis and the wide wall are perpendicular to the axis of the device, and the cathode with the external tube forming the coaxial line. The external tube is located on the cover of the process chamber outside the cathode with the spacing and isolated from it electrically. At that in this spacing there is the swirler of the gas stream and in one of the walls of the waveguide there is the mounted fitting pipe for inlet of the reducing gas, and the magnet system is mounted round the external tube. The internal pipe is the second anode. In the conditions of maintaining the SHF discharge under the butt of the cathode and in the spacing between it and the internal tube in the strong axial magnetic field the electric arc excited in this spacing exits from the spacing, moves along the butt of the cathode and heats up it uniformly along the whole surface. It easies the start of the main arc, allows to maintain the diffuse nature of the arc and to ensure the decrease of erosion of the cathode and the increase of the device productivity due to the increased operational periods between the periods of the cathode replacement or the procedures of its building up.

EFFECT: the invention ensures the easy start of the main arc, maintaining the diffuse nature of the arc, the decreased erosion of the cathode, the increased productivity of the device.

9 cl, 2 dwg

Description

The field of technology.

The invention relates to non-coke metallurgy, in particular to the production of billets by reducing metal oxides from metal-containing oxide raw materials, such as dispersed ores, ore concentrates, metal-containing oxide wastes and partially reduced ores, by gaseous and dispersed reducing agents in plasma-chemical reactors, the bulk of the energy of which is introduced using an arc discharge.

The level of technology.

Devices for direct reduction of metals based on arc discharges are described in the well-known technical literature ("Industrial electric furnaces. Arc furnaces and special heating installations." / Ed. Svenchansky AD - M. Energoizdat, 1981, p. 251, 247). Typically, the device comprises a molten bath with metal and slag collection means, feed means for supplying raw materials and a plasma-forming gas, a solenoid and a working electrode located on the central axis made of graphite or tungsten. In some cases, the source material and plasma-forming gas are supplied through the cavity of the working electrode, which is usually installed in the upper part of the device, and it is the cathode of the arc plasmatron; the molten metal bath located on the bottom of the furnace plays the role of the anode.

A common drawback of these devices is the presence of a consumable electrode - a cathode, which requires a process stop to replace the cathode. Even in the case when the electrode is not replaced, but is increased and moved to the working area by means of the devices provided for this (RF patents Nos. 1781306 and 2007463), the process remains intermittent due to the need to disconnect the ore feed means from the central electrode - the cathode at the time of installation of the backup electrode and cleaning of the elements of the device, and the final material is contaminated by cathode erosion products. In addition, it is practically impossible to ensure a stably uniform stay of the processed material in the arc region due to the significant size of the molten bath mirror and random movement along the working surface of the electrode of the contracted arc spot due to the relatively low temperature of the end of the cathode. At the same time, energy costs are high for heating the gaseous medium, a significant part of the energy of which is irretrievably lost, despite attempts to reuse it ("Development of Coxless Metallurgy". / Ed. By N. Tulin, K. Mayer - M .: Metallurgy, 1987 g., Pat of Russia No. 2037524).

Replacing a graphite or ceramic bath with a bottom electrode in a metal collecting device with a metal cooled crystallizer (US Pat. No. UK 1,554162) eliminates metal contamination with the bottom electrode material, but does not solve the problem of pollution and increased consumption of the central electrode — the cathode.

In a wide variety of plasma technologies based on the implementation of nonequilibrium effects, discharge volume and controllability of the main plasma characteristics in the absence of electrodes consumed in the technological process, microwave plasma can be used (e.g. Pat. RF No. 1602376, 2149521, 2225684). The disadvantages of devices based on microwave plasma-chemical technologies are associated with low productivity of the equipment due to the small amount of energy introduced into the discharge.

The closest prototype of the invention is a plasma furnace for direct reduction of metals, containing a cooled working chamber with a lid and a device for collecting the finished product, a charge feeder, a charge input device and means for introducing reducing gas into the working chamber, a hollow cathode mounted on a central axis with the possibility of movement, moreover, the anode is combined with a collecting device, and a magnetic system (US Pat. RF No. 2007463).

In this device, the mixture and the reducing gas are introduced through the cavity of the cathode; the wear of the cathode (usually graphite) is mainly determined by two factors: chemical - due to partial ore reduction due to the electrode material and thermal - due to the evaporation of the cathode material due to its uneven heating by the ion current of the arc to the cathode. At the same time, there is a process of narrowing of the cathode cavity due to the deposition of carbon on it, formed as a result of pyrolysis when using hydrocarbons as the reducing gas. At the initial stage of the melting period, when the arc burns onto cold metal, frequent arc breaks occur (A.V. Smirnov. Controlling the movement of electrodes in an arc furnace in extreme situations. Electrometallurgy, 2001, No. 6, p.21).

SUMMARY OF THE INVENTION

The technical problem solved by the proposed device is to increase the productivity of the furnace, reducing the cost of production and increasing the stability of the furnace.

The technical result consists in reducing the erosion of the cathode and facilitating the launch mode.

This result is achieved due to the fact that the means for supplying microwave energy to the working chamber is introduced into the furnace and the charge input device is made in the form of a cooled internal electrically conductive tube placed in the cathode cavity with a gap and electrically isolated from it.

In this case, the microwave energy input means is made in the form of a coaxial waveguide transition, consisting of a rectangular waveguide, the axis and wide wall of which are perpendicular to the axis of the device, and an external tube placed on the lid of the working chamber outside the cathode with a gap and electrically isolated from it, and a gas flow swirl is installed in this gap, the magnetic system is around the outer pipe and a reducing gas inlet pipe is placed in one of the walls of the waveguide. The cathode and outer tube form a coaxial line.

In addition, dielectric fastening rings are introduced in the gap between the cathode and the inner tube, a microwave choke is installed on the coaxial waveguide junction, which is separated from the central electrode by a dielectric insulator, the inner tube is an additional (second) anode, the charge feeder is connected to the inner tube through an insulator, an additional magnetic system is installed around the product collection device, a microwave discharge initiating device is installed in the side wall of the working chamber, the furnace is equipped with an extension device anija and / or moving the cathode, and the lower end of the inner tube is recessed from the lower face of the cathode.

Our theoretical and experimental studies have shown that under conditions of maintaining a microwave discharge under the end of the cathode and in the gap between it and the inner tube — the second anode in a strong axial magnetic field, the electric arc excited in this gap leaves this gap and moves along the end cathode. As a result, the end of the cathode warms up, no pronounced arc binding is observed, and a diffuse mode of arc burning is ensured.

Terms used.

Plasma furnace - a device containing two or more electrodes between which an electric discharge is excited in a plasma-forming gas medium, controlled by gas or magnetodynamic methods, the plasma of which is used to heat the gas, melt and recover ore materials.

Feeder - a device, usually containing a bunker with the original ore raw materials and means for feeding it at a given speed.

The device for collecting the finished product - a device that is usually made in the form of a hearth or mold.

The hearth is usually a cooled metal bucket containing a protective ceramic lining, holes for the release of metal and slag; graphite masonry may be introduced between the lining and the metal of the bucket. Usually one of the electrodes of the furnace (anode) is built into the hearth.

A crystallizer is a device for recovering ore raw materials and collecting a product, a metal, in which the molten metal is cooled to a solid state to obtain a slab. In the case of slag formation, the mold is provided with an opening for its output.

A slab is a semi-finished product, which is a metal billet of rectangular cross section with a large ratio of width to height, prepared for further processing, for example, rolling, forging, etc.

The mixture is a mixture consisting of ore raw materials (ore, concentrate), alloying and refining additives.

Ore, iron ore raw materials - mineral or man-made raw materials containing one or more oxides, for example, iron of various valencies.

Coaxial - waveguide transition - a device for converting a microwave wave of a coaxial line into a microwave wave propagating in a waveguide, and vice versa. Usually consists of a coaxial line, made in the form of external and internal conductors, and located perpendicular to its axis of a rectangular waveguide. The configuration of the fields of a microwave wave excited by a rectangular waveguide in a coaxial line is determined by the ratio of the transverse dimensions of its conductors and the orientation of the walls of the waveguide relative to its axis. To prevent microwave radiation into the surrounding space from the side of the transition opposite the coaxial line, its conductors should be closed at a distance close to a quarter of the wavelength, and if necessary, provide electrical isolation between them - a device should be installed that simulates such a short circuit - a microwave choke , or a dielectric absorbent material should be placed in the gap between the conductors.

Description of the drawings.

Figure 1 schematically shows a longitudinal section of a preferred embodiment of the device.

Figure 2 presents the cross section of the device.

The device comprises a charge feeder 1, a cathode 2, a working chamber 3 with a cover 4 and a device for collecting the finished product 5 in the form of a hearth, anode 6, an internal metal cooled pipe 7, an external metal pipe 8, a coaxial waveguide transition 9 with a coaxial part 10 and a rectangular a waveguide 11, a reducing gas input 12, a solenoid 13, a gas flow swirl 14, a microwave discharge initiation device 15, mounting dielectric insulators 16, 17 and 18, a microwave inductor 19, an additional magnetic system - solenoid 20, outlet leads and the exhaust gas 21, the openings of manufacture of the finished product 22, an insulating dielectric insulator 23, dielectric window 24.

The lower end of the inner tube 7 is recessed relative to the lower end of the cathode 2, and its upper end is connected to the feeder 1 through the insulator 22. The anode 6 of the furnace is combined with the collecting device 5, the inner tube 7 is an additional (second) anode. The outer tube 8 is mounted on the cover 4 of the working chamber 3 and together with the cathode 2 forms a coaxial line connected to the coaxial-waveguide transition 9. The axis of the waveguide 11 and its wide wall are perpendicular to the axis of the device, the reducing gas input 12 is placed in one of the walls waveguide 11. A solenoid 13 surrounds the cooled external pipe 8 above the working chamber 3. In the same section, in the gap between the hollow electrode 2 and the external pipe 8, a dielectric gas flow swirl 14 is installed, simultaneously performing the role of the lock gap. The same role of the gap retainers is performed by insulators: 16 - in the upper part, 17 - in the lower part of the gap between the cathode 2 and the tube 7, 18 - between the electrode 2 and the inductor 19. The inductor 19 prevents microwave radiation into the surrounding space and can be constructed not necessarily the one presented here. For example, a dielectric material absorbing microwave energy can be placed in the gap between the cathode 2 and the extension of the outer tube above the waveguide 11.

In the wall 4 of the chamber 3 is placed the commonly used device for initiating the microwave discharge 15, made in the form of a metal pin, briefly inserted into the chamber 3. The initiation of the microwave discharge can be performed in another way (for example, by briefly touching the cathode 2 of the anode 6 with a low voltage between them, using the starting plasmatron, high-frequency breakdown, etc.). In one of the walls of the chamber 3 (in this case, in the side), exhaust gas outlet pipes 21 are installed, and a second solenoid 20 is located under the chamber 3. Window 24 seals the furnace.

The implementation of the invention.

The device operates as follows. The standard values of electric potentials are established on the electrodes: on the cathode 2 — negative, on the inner tube 7 — intermediate between the zero potential of the first anode 6 and the potential of electrode 2 (the possibility of such a potential setting on the pipe 7 is provided by its electrical isolation from other electrodes of the furnace). A charge mixture is placed on the collecting device 5 and the anode 6 and reducing gas is supplied to the region of the lower end of the cathode 2. A part of the reducing gas can be supplied through the pipe 7 together with the charge. Coolant is shaken between the outer and inner walls of the pipe 7.

Microwave energy is supplied into chamber 3, a microwave discharge device 15 initiates a microwave discharge and an auxiliary arc between the cathode 2 and the pipe 7 (additional anode). In the preferred embodiment presented here, the means for supplying microwave energy to the chamber 3 is made in the form of a coaxial waveguide transition 9 consisting of a rectangular waveguide 11 and a coaxial line 10 formed by the cathode 2 and an external tube 8 fixed to the chamber 3. However, the supply of microwave energy into the chamber 3 can also be implemented by other means, for example, a rectangular waveguide connected laterally to the wall of the chamber 3 (US Pat. RF No. 1602376), or microwave energy input units connected directly to the cover and / or bottom of the camera 3 (US Pat. No. 214 3794). In all these options, the main condition for the feasibility of the claimed technical result is provided - the creation of a microwave discharge plasma under the lower end of the cathode 2.

The plasma of the microwave discharge and the auxiliary arc, propagating towards the anode 6, partially restores the bulk of the raw material on it and melts it. The plasma of the auxiliary arc fills the entire space between the electrodes and ensures reliable excitation of the arc of the main discharge. After that, through the inner tube 7, the charge from the feeder 1 is fed into the working chamber 3.

The recovered metal is either drained through hole 22 using a hearth, or is cooled and drawn out if a mold is used.

The physical effect used in the present invention, consisting in the diffuse nature of the arc burning, in which current sampling is carried out uniformly from the entire surface of the end of the cathode 2 at a current density substantially lower than in the prototype, was possible due to the fact that the auxiliary arc in the axial magnetic field of the solenoid 13 leaves the gap between the cathode 2 and the second anode 7 under the lower end of the cathode 2 and in the presence of a microwave discharge heats it uniformly over the entire surface. If the very possibility of creating a diffuse mode of arc burning using an auxiliary arc (AS USSR No. 5434891) is known, it was possible to reliably ignite and bring the auxiliary arc under the end of cathode 2 only with the help of a microwave discharge. The uniformity of the heating of the end face of the cathode 2 is facilitated by the gas circulation created by the swirler 14.

In addition, a microwave discharge in the near-cathode region of the main arc stabilizes it, since even with possible hopping of the arc observed in known devices, the microwave discharge plasma filling this region does not allow the current to cease with a break in the main arc.

To ensure electrical isolation, the outlet pipe of the feeder 1 can be introduced into the pipe 7 with a gap, but their mechanical connection through the insulator 23 fixes their relative position.

In the proposed device, the consumption of the cathode 2 is reduced many times in comparison with the prototype and this dramatically increased the time of its continuous operation, however, the cathode 2 must be moved towards the chamber 3, albeit much more slowly than in the prototype, and as the upper end of the cathode 2 approaches the throttle replace it or build up. Given the large axial size of the device and, accordingly, the large length of the remaining part of the cathode 2, it is advisable not to replace it, but to build up a backup electrode using a device, for example, similar to the prototype. In this case, the feeder should have transverse dimensions smaller than the diameter of the cathode 2 cavity, and the moving device (not shown in the drawing) is connected to the electrode 2 in the working position. The pipe (not shown) supplying the charge to the feeder 1 is disconnected from it, and the system hoses cooling (not shown) is disconnected from the pipe 7 and taken to the side, the cathode 2 is clamped (not shown), the backup electrode is connected to the cathode 2, for example, by means of a thread intended for this at their ends, the moving device from the cathode 2 is disconnected and connect it to the backup electrode, release the cathode 2 from the retainer, return the supply pipe and hoses of the cooling system to their place and continue the process.

An additional magnetic system 20 enhances the magnetic field, which rotates the arc and molten metal on the platform 5, increasing the efficiency of the interaction of the charge with the reducing gas and the uniformity of the finished product.

The deepening of the inner tube 7 relative to the lower end of the cathode 2 prevents the main arc from jumping to the tube 7 and its destruction, and the amount of deepening is determined by the operating mode of the furnace.

Thus, the excitation of the microwave discharge provided the removal under the end of the cathode 2 of the auxiliary arc formed by the discharge between it and the additional anode 7 located in its cavity, and made it easier to start the device. In addition, in the microwave discharge plasma, the auxiliary and main arcs became stable, which ensured the stability of the furnace, while maintaining the diffuse nature of the arc ensured a decrease in cathode 2 erosion and an increase in device productivity due to an increase in the operating periods between replacements or cathode build-up procedures.

At the same time, the creation of a stable diffuse plasma formation improves the recovery process, increasing the overall productivity of the furnace and reducing the cost of production.

Claims (9)

1. Plasma furnace for direct reduction of metals, containing a cooled working chamber with a lid and a device for collecting the finished product, a charge feeder, a charge input device and means for introducing a reducing gas into the working chamber, a hollow cathode mounted on the central axis of the furnace with the possibility of its movement, anode combined with a collecting device and a magnetic system, characterized in that it is provided with means for supplying microwave energy to the working chamber, the charge input device is made in the form of a cooled internal electric wire hydrochloric tube placed in the cavity of the cathode with a gap and electrically insulated from it. 2. Plasma furnace according to claim 1, characterized in that the means for supplying microwave energy is made in the form of a coaxial waveguide transition, consisting of a rectangular waveguide, the axis and wide wall of which are perpendicular to the axis of the furnace, and forming a coaxial line of the cathode and the outer tube placed on the lid of the working chamber outside the cathode with a gap and electrically isolated from it; moreover, a gas flow swirl is installed in this gap, a reducing gas inlet pipe is installed in one of the waveguide walls, and a magnetic system is installed in district of the outer pipe. 3. The plasma furnace according to claim 2, characterized in that on the outer tube above the coaxial waveguide junction, a microwave choke is installed, separated from the cathode by a dielectric insulator. 4. The plasma furnace according to claim 1, characterized in that the inner tube is an additional anode. 5. Plasma furnace according to claim 1, characterized in that the charge feeder is connected to the inner pipe through an insulator. 6. The plasma furnace according to claim 1, characterized in that a device for initiating a microwave discharge is installed in the side wall of the working chamber. 7. The plasma furnace according to claim 1, characterized in that an additional magnetic system is installed around the collector or below it. 8. The plasma furnace according to claim 1, characterized in that it is equipped with a device for increasing and / or moving the cathode. 9. A plasma furnace according to any one of claims 1 to 8, characterized in that the lower end of the inner tube is recessed relative to the lower end of the cathode and dielectric fastening rings are introduced into the gap between it and the inner tube.

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