RU2318876C1 - Apparatus for direct reduction of metals - Google Patents

Abstract

FIELD: coke free metallurgy, namely production of continuously cast billet by direct reduction of metal from metal containing oxide raw material.

SUBSTANCE: reduction is performed by means of gaseous and dispersed reducing agents in plasma-chemical reactors in which main part of energy is introduced by means of arc discharge. Apparatus includes unit for supplying reducing gas and charge, electric ac furnace, unit for moving and changing working electrode and magnetic system. Electric arc furnace includes reactor with cooled walls, two different polarity electrodes mounted coaxially relative to vertical axis of reactor and unit for collecting ready product. In cavity of upper working electrode cooled tube joined with working electrode is mounted. Annular turnings are formed on outer surface of working electrode. Unit for collecting ready product is in the form of metallic cooled crystallizer. Charge and reducing gas are fed through cooled tube preventing penetration of charge onto working electrode and its rapid consumption. It is possible to use any gaseous reducing agent including natural gas at temperature lower than its pyrolysis temperature.

EFFECT: possibility for producing homogenous metal with small content of impurities.

4 cl, 2 dwg

Description

Technical field

The invention relates to non-coke metallurgy, in particular to the production of a continuously cast billet by reducing metals, not only iron, from metal-containing dispersed oxide raw materials such as ores, including partially reduced ores, ore concentrates and metal-containing oxide waste, gaseous and dispersed reducing agents in plasma-chemical reactors, the main share of the energy into which is introduced using an arc discharge.

State of the art

As is known, a method in which iron is produced by reducing iron ore bypassing blast furnace production is classified as a “direct reduction method”. Methods of direct reduction of metals and corresponding devices based on arc discharges are described in the well-known technical literature ("Industrial Electric Furnaces. Arc Furnaces and Special Heating Units." Edited by AD Svenchansky - M .: Energoizdat, 1981, p. 251, 247). Typically, the device contains a molten bath with means for collecting metal and slag, means for supplying feedstock - a charge and a working gas, a solenoid and a working electrode located on the central axis made of graphite or tungsten. In some cases, a charge and a working gas are supplied through a working electrode, usually located in the upper part of the device, and it is an arc discharge cathode; the role of the anode is played by a molten metal bath located on the bottom of the furnace.

A common disadvantage of these devices and methods is the presence of a consumable cathode electrode, the limited volume of the melting chamber, and the intensive destruction of its lining upon contact with oxide melts. This requires a periodic shutdown of the process for the release of metal, replacement of the cathode and walls of the melting chamber of the reactor, protected by graphite or ceramic lining (for example, Russian patents Nos. 2022491, 2072639, No. 2002930).

Even in the case when the electrode is not replaced, but increased by means of devices provided for this (RF patents Nos. 1781306 and 2007463), the process remains intermittent due to the limited capacity of the furnace and the need to disconnect the charge supply means from the cathode during the installation of the backup electrode and the final material is contaminated by the products of erosion of the furnace lining.

Replacing a graphite or ceramic lining in a metal collecting device with a baking electrode with a metal cooled mold (US Pat. Great Britain No. 1054162) in known devices does not completely solve the aforementioned problem due to the increased consumption of the working electrode and metal contamination by its erosion products.

The closest prototype of the present invention is a device for direct reduction of metals, containing means for supplying reducing gas and a charge, an electric arc furnace with means for collecting the finished product, including a reactor with cooled walls, two bipolar electrodes placed coaxially on the vertical axis of the reactor, one of which (upper working the electrode) is made hollow and articulated with a cooled pipe, a device for moving the working electrode and the magnetic system surrounding the reactor (US Pat. RF No. 2007463). In this device, the second electrode (anode) is a molten bath placed in a ceramic crucible, reducing gas and a charge are supplied to the reactor through a hollow working electrode, a cooled pipe is installed outside this electrode and serves to seal the chamber and cool the working electrode, the reactor and the hearth are equipped with graphite and ceramic masonry, and a device for moving and building was introduced to build up the working electrode.

Despite the measures taken, this device failed to combine the requirements for lowering the temperature of the supplied gas to prevent its pyrolysis and maintaining a high temperature of the end of the working electrode, which is necessary to reduce its erosion due to the presence of sedentary contracted spots.

SUMMARY OF THE INVENTION

The present invention solves the technical problem of improving the quality of the metal and increasing the productivity of the process of its production.

The main technical result of the use of the invention is to increase the duration of the periods of operation of the furnace between replacements of the working electrode, to reduce the consumption of material of the working electrode and to use any gaseous reducing agent without the risk of coking of the input channel.

In addition, the problem of reducing pollution of the finished product by erosion materials of the working electrode, reactor screen and furnace lining is additionally solved.

This result is achieved by the fact that the cooled pipe is installed inside the working electrode, and annular grooves are made on the outer surface of the electrode. The lower end of the pipe is recessed relative to the lower end of this electrode by an amount of 1-1.5 of the diameter of the electrode cavity, the ratio of the external and internal diameters of the working electrode is selected from a ratio of 3-5. As a means of collecting the finished product used metal cooled mold. The graphite screen is removed.

Terms and definitions used.

An arc furnace is 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.

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

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

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.

Synthesis gas is a gas mixture whose main components are carbon monoxide and hydrogen.

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

Iron ore raw materials - mineral raw materials containing one or more iron oxides of various valencies.

Poor ore raw materials - raw materials with a metal content of less than 60%.

Rich ore raw materials - raw materials with a metal content of about 70%.

Description of the drawings.

Figure 1 schematically shows a variant of the device in longitudinal section.

Figure 2 shows the cross section of the device in the plane aa.

The device comprises a charge feeder 1, a reducing gas source 2, an arc furnace reactor 3 with metal cooled walls 4 and a vault (cover) 5, including a hollow working electrode 6 with annular grooves 7 on its outer surface, a means for collecting 8 finished product (crystallizer) with the collection platform 9 on the drive rod 10 in the receiving chamber 11 and the cooled pipe 12. To move and change the working electrode 6, as well as the movement of the pipe 12 is the drive 13. In the wall 4 of the reactor 3 there is a pipe 14 for exhaust gas, and ug reactor 3 - a magnetic system in the form of a solenoid 15. Between the electrode 6 and the cover 5 of the reactor 3 is installed a seal 16 from an insulating material.

External to the reactor 3 part of the electrode 6, the pipe 12 and the moving device 13 are separated from the surrounding space by a casing 17 mounted on the cover 5 through an electrical insulator 18.

The pipe 12 serves as a channel for supplying the charge and reducing gas from the feeder 1 and the gas source 2 to the reactor 3 and is installed in the cavity of the working electrode 6. The lower end of the pipe 12 is located at a distance of 1-1.5 of the inner diameter of the working electrode 6 from its lower end.

The working electrode 6 and the pad 9 are the electrodes of the reactor 3, their polarity can be either direct (the working electrode 6 serves as the cathode) or the reverse (the working electrode 6 serves as the anode). The ratio of the outer and inner diameters of the electrode 6 is in the range of 3-5, the width and depth of the annular grooves 7 are 0.1-0.2, and the interval between them is 0.5-1 of the outer diameter of the electrode 6.

The implementation of the invention.

The operation of the device with the direct polarity of the electrodes of the reactor 3 is illustrated. A metal “seed” is loaded onto the collection site 9, voltage is applied to the electrodes of the reactor 3 and an arc discharge is excited therein using one of the known methods, for example, by briefly touching the “seed” working electrode 6 using the starting plasmatron, high-frequency breakdown, etc. Pipe 12 is supplied with reducing gas and at relatively low relative to the nominal values of the arc current and voltage induce on the site 9 "swamp" of metal "seed". Then set the operating parameters of the installation: the induction of the magnetic field of the solenoid 15, the magnitude of the arc gap between the electrode 6 and the molten metal on the site 9, the magnitude of the arc current, the flow rate of the reducing gas through the pipe 12 and the reactor 3 from the gas source 2.

After pointing the "swamp", i.e. melt at the site 9, the feeder 1 through the pipe 12 into the reactor 3 serves a mixture consisting of ore raw materials (ore, concentrate), alloying and refining additives. The mixture of charge and gas enters the melt, while the mixture is restored to metal. The reduced metal as a heavier fraction is lowered into the lower part of the mold 8 on the platform 9, where a hard shell of the billet is formed - an ingot, for example a slab, which is pulled from the mold 8 by the pulling mechanism (not shown) as the metal accumulates using the rod 10 into the finished metal receiver 11. The exhaust gas is discharged through the pipe 14.

The cooling of the gas supply channel (pipe 12) allows you to feed natural gas into the reactor 3 at a temperature below the gas pyrolysis temperature, which does not require its conversion. Moreover, due to the fact that the area of thermal contact of the pipe 12 and the working electrode 6 can be placed far enough from the lower end of the electrode 6, the temperature of the latter can be ensured taking into account the need to form a diffuse arc spot on the end of the electrode 6, characterized by a uniform and reduced production of the electrode material 6.

The annular grooves 7 on the outer surface of the electrode 6 increase the longitudinal thermal resistance of the electrode and increase the temperature of the lower end of the electrode 6 and the formation of a diffuse spot, as well as reduced heat transfer to the pipe 12 in the area of thermal contact. When the ratio of the diameters of the electrode 6 is less than three, the current density in it increases, which causes its increased consumption, and when the ratio of the diameters of the electrode is more than five, the possibilities for placing the reagent supply channel (pipes 12) in it are greatly reduced.

Placing the lower end of the pipe 12 at a distance from the lower end of the electrode 6 larger than 1.5 of the diameter of its cavity leads to a significant hit of the charge on the working electrode at high temperature (about 3000 ° C), and its increased wear, and when removed less than 1, 0 the diameter of the cavity of the electrode 6 increases sharply the probability of jumping the discharge arc to the pipe 12 and its destruction.

The use of a cooled pipe 12 in the cavity of the electrode 6 allows you to deliver the mixture and cold reducing gas to the device for collecting the finished product - crystallizer 8 - in the axial zone of the reaction volume of the plasma arc. Due to the axial magnetic field of the solenoid 15, the azimuthal rotation of the arc and the molten bath is ensured, which leads to uniform heating and active interaction with the reducing gas of the entire mass of the incoming charge and to obtain a homogeneous metal. In this case, it is necessary to limit the transverse dimensions of the means of collecting the finished product and ensure its effective cooling. These conditions are most consistent with the use as a means of collecting metallic cooled mold 8.

The implementation of the mold 8 from an electrically and thermally conductive material chemically resistant to oxide melts and its effective cooling in the presence of an axial magnetic field prevents it from being burned by an arc discharge, eliminates ceramic lining and graphite masonry, and ultimately produces a metal of the required composition with a small content of harmful impurities.

Using the device 13 for moving and building up the working electrode 6, similar to the prototype, allows the process to be practically continuous. With a large wear of the electrode 6, the feeder 1 and the gas source 2 are disconnected from the pipe 12, the pipe 12 is removed from the electrode cavity 13 by the device 13, then the working electrode 6 is fixed by the clamping mechanism (not shown) of the device 13, and it is expanded with a spare electrode using a thread at the ends of both electrodes connect the spare electrode to the displacement mechanism of the replacement device, release the electrode 6 from the clamp, and continue the process. During the build-up, the working electrode 6 is not removed from the volume of the reactor 3 and the arc discharge is not de-energized.

Thus, the present invention allows:

- use any gaseous reducing agents: synthesis gas, hydrogen, unconverted natural gas due to the supply of reagents to the reaction volume of the furnace through a cooled metal pipe 12;

- reduce the consumption of the working electrode 6 by eliminating its contact with the charge when it is fed into the working space of the reactor 3 and the formation of a diffuse cathode spot by increasing the temperature of the end face of the electrode 6;

- to obtain a homogeneous metal with a low content of impurities (for example, carbon) due to the use of gaseous reducing agents and the rejection of the use of coke, and using a metal mold 8 and a magnetic field to ensure uniform heating and effective interaction with the reducing gas of the entire mass of the incoming charge and to exclude the contact of the melt with ceramic lining;

- increase the time of continuous operation of the device by reducing the start-up time, reducing the consumption of the electrode 6 and the use of a cooled metal mold 8, practically not subject to wear.

The invention can be used at the enterprises of metallurgy and engineering for the direct production of cast metal billets from dispersed ore materials using gaseous and dispersed reducing agents, including unconverted natural gas and hydrogen.

The environmental indicators of the proposed method and device are significantly higher than that of analogues: coke is not consumed, agglomeration and pelletizing of ore raw materials are not required, it is possible to work on hydrogen and on raw natural gas.

Test melting with the reduction of dispersed ore and ore concentrate was carried out on a direct-polar experimental arc plant with a graphite electrode and using methane (an analogue of natural gas) as a reducing agent. With a plasma arc power of 70 kW, a direct reduction process was carried out to obtain iron in the form of an ingot with a diameter of 100 mm with a total impurity content of not more than 1.5%.

The possibility of realizing all the effects accompanying the process of supplying a charge and a reducing gas to the reactor through a cooled pipe with metal reduction in a molten bath proposed in the present invention was first established by us and has not been published anywhere.

According to the prepared terms of reference, the metallurgical complex enterprise manufactured a pilot plant in accordance with the invention at an arc power level of 0.2 MW.

Claims (4)

1. A device for direct reduction of metals, containing means for supplying a reducing gas and a charge, an electric arc furnace with means for collecting the finished product, including a reactor with metal cooled walls, two bipolar electrodes placed coaxially with the vertical axis of the reactor, while the upper working electrode is hollow and articulated with a cooled pipe, a device for moving and changing the working electrode and a magnetic system surrounding the reactor, characterized in that the cooled pipe is installed in the cavity a working electrode with the possibility of supplying reducing gas and a charge thereto to the reactor, the lower end of the chilled pipe being buried relative to the lower end of the working electrode, and circular grooves are made on the outer surface of the working electrode. 2. The device according to claim 1, characterized in that the lower end of the cooled pipe is recessed relative to the lower end of the working electrode by an amount of 1-1.5 diameter of the electrode cavity. 3. The device according to any one of claim 1 or 2, characterized in that the ratio of the external and internal diameters of the working electrode is 3-5. 4. The device according to claim 1, characterized in that the means for collecting the finished product is made in the form of a metal cooled crystallizer.

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