RU2063598C1 - Electric resistance furnace - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: electric furnace has heat-insulated housing with inner refractory lining and graphite tubular heater, current supply devices, charge heating and melting reservoir formed by inner surface of graphite hearth heater and graphite hearth and connected with iron accumulating and preheating reservoir by hearth flue fitted with shut-off fittings; this reservoir is formed by inner surface of lined walls of furnace housing, outer surface of graphite hearth heater and graphite hearth and is connected with metal refining and finishing reservoir by means of flue fitted with shut-off fittings; this reservoir is bounded by refractory lining of furnace. Several graphite hearth heaters may be arranged inside furnace housing; their number shall be multiple to three; they are connected to electric supply circuit by star connection; graphite hearth closes heaters from below, phase conductors are connected to upper portion H and neutral wire of graphite hearth heaters is connected to graphite hearth; metal refining and finishing reservoir is tight and is provided with plasma unit for preheating and feeding oxygen, refining and alloying additives. EFFECT: enhanced efficiency. 12 cl, 2 dwg

Description

 The alleged invention relates to the field of metallurgy.

 Known designs of furnaces for the recovery of metals from their compounds by heating these compounds / oxides, sulfides, etc. / and in a mixture with a reducing agent / coal, coke, etc. /, in which heat is released as a result of combustion / oxidation / of the same reducing agent. This type of furnace is a casing lined from the inside with refractory masonry. The furnace usually has a device for loading the charge and the release of metal and sludge, supplying a reducing agent and removing gaseous products of combustion and other reactions / 1,2 /.

 The disadvantage of this type of furnace is the inability to strictly separate control of the temperature and atmosphere in the furnace. Despite the sometimes used soda cleaning of fuel supplied to the furnace from impurities, the fuel always contains compounds in which elements harmful to the process are present, such as sulfur, phosphorus, etc. that degrade the quality of the metal, or even make it impossible to smel it.

 Also known are the designs of electric furnaces for smelting metals, including arc, induction and resistance furnaces / 3, p.111 /. Electric furnaces favorably differ from fuel furnaces in the ability to maintain a given atmosphere in the furnace and in the absence of metal pollution from the products of fuel combustion. Only with the use of electric furnaces it was possible to obtain high-quality steels, to melt non-ferrous metals / titanium, aluminum, etc. / 4 /.

High-temperature electric furnaces with a working temperature above 1250 ^o C, working without a protective atmosphere or vacuum, are made with heaters from carborundum and molybdenum disilicide / 4,5 /. Heaters of this type are easily destroyed, require a special mode of heating and cooling. In furnaces with a protective environment, heaters made of refractory metals / molybdenum and tungsten / and graphite have become widespread. Due to the high cost of the furnace with tungsten and molybdenum heaters, they are used only when the presence of graphite in the furnace is unacceptable.

 A known design of a shaft electric furnace with a graphite heater / 5, p.32, 6, p.149 /. The furnace contains a housing with thermal insulation with an internal refractory lining, inside of which is placed a graphite tubular heater equipped with a current supply device. The furnace contains only one chamber for placing a vessel for heating and melting the charge in the form of a crucible inside the tube cavity and a loading device, therefore, it can only serve for crucible melting of metals, which is characterized by an extremely low productivity.

 The disadvantage of this device is its low performance.

 The closest in technical essence and the achieved result is an electric resistance furnace for smelting steel from an iron ore charge, containing a thermally insulated body lined with refractory, underneath, a graphite heater with current supply devices located in the inner cavity of the lined body, a melting space and a loading device connected to the melting space / 6 /. Under the known device is made of non-conductive material, therefore, heat in the furnace is released by passing current between the electrodes immersed in slag, which is a disadvantage, because the electrical resistance of the slag during melting is constantly changing due to changes in its chemical and phase composition, in accordance with this, the thermal parameters of the melting are constantly changing, which makes the process unstable. This is indicated by the data given in the mentioned book on fluctuations in the content of carbon (0.5-4%) and silicon / 0.1-13% / in the smelting. Therefore, in a furnace of known design, it is possible to smelting only ferrous metal, which needs subsequent refinement. Such a refinement in the known device is impossible, because it is not equipped with additional containers for its implementation.

 The present invention proposes, in contrast to the known device, to make a graphite heater made in the form of a pipe under it from an electrically conductive material, in particular graphite. In this case, the melting space is formed by the inner surface of the graphite heater and the hearth and is connected by a hearth channel equipped with shutoff valves with a capacity for accumulating and heating cast iron, which is limited by the inner surface of the lined walls of the furnace body, the outer surface of the graphite heater and the hearth, the latter being a channel with a shutoff fittings with a container for refining and finishing metal, limited by the refractory lining of the furnace body. 2 Inside the furnace body, Several tubular graphite heaters with a multiple of three included in the power circuit to a “star” were installed, with the heaters closing at the bottom, phase conductors connected to the top of the heaters, and the neutral conductor connected to the bottom of the furnace.

 The metal refining and lapping capacity is sealed and equipped with a plasma installation for heating and supplying oxygen, refining and alloying additives.

 The stated constructive solution allows, in contrast to the known one, to solve the problem of stabilizing the temperature of the iron reduction process, because heat is released not in a slag layer of variable electrical conductivity, but in a graphite heater, which has constant electrical resistance during melting. The organization of additional containers for the accumulation and heating of cast iron, refining and finishing of metal allows stabilizing the chemical composition and obtaining the metal of the necessary substance.

 The proposal is illustrated by drawings, where in FIG. 1 shows the appearance of the design of the furnace in a three-phase embodiment. In FIG. 2 shows a diagram of the connection of heaters with their number equal to three.

 The electric furnace is a housing 1 with thermal insulation 2, inside of which are placed heaters 3 in the form of vertically arranged graphite pipes. The upper device for current supply 4, connected to one of the phases of the power source, is made in the form of a system of bushings filled with graphite grains or graphitized fabric with the possibility of elongation of the pipe due to thermal expansion, for example, as described in the source / 5 /. The lower current supply is provided by adjoining the end of the pipe to the conductive hearth of the furnace 5, made of graphite and connected to the neutral conductor of the voltage source. The cavity of the graphite pipe and under the furnace form a container for heating and melting the charge "a". In turn, the walls of the pipes 3, under the furnace 5, the walls of the furnace 2 form a container for the accumulation of metal "b". Adjacent to this tank is a tank for refining and fine-tuning metal “c”, connected to tank “b” with channel “g”. Tanks “a” and “b”, in turn, are connected by a hearth channel “d” equipped with a shut-off device 6. The tank “c” is lined with carbon-free material and equipped with a plasma torch 7 and nozzle 8 for supplying an inert gas or oxidizing agent as necessary oxygen or air. In the lining of the tank there is a channel "e" for the release of finished metal. Tanks "b" and "c" channel "g" are connected and the hole in the channel can be blocked by shutoff valves 6a.

 Like channel "d" in the lining of the tank "b" there are channels with a locking device (not shown) for the release of slag into the tank "G" of the cart 9. The furnace is also equipped with collectors 10 for the removal of gaseous products of metal reduction reactions. In the upper part of the tank "a" there are devices for loading charge materials made in the form of funnels 11 and 12 with a lock chamber "z" located between them. The inlet and outlet openings of the lock chamber are overlapped by return cones 13 and 14 provided with actuators 15 and 16.

 Graphite under 5 closes the heaters 3 from the bottom, the phase conductors are connected to the top of the heaters 3, and the neutral conductor is connected to the bottom of the furnace 5, thereby achieving a star connection. A feature of the hearth channel "d" is that it is made in the form of a siphon, which on the side of the tank "b" ends with a sleeve 17, the height of which is determined from the following considerations. In the tank "a" metal is gradually reduced and flows into the channel "d". At the same time, slag is formed in tank "a". In the accumulation mode in the tank "b" of metal slag should not fall into the tank "b", but should remain in the tank "a".

 For three heaters / FIG. 2 / graphite under 5 is connected to the neutral conductor "O", and the phase conductors "a", "b", "c" are connected respectively to graphite heaters 3a, 3b, 3c. This avoids phase imbalance in the supply network.

 Electric furnace works as follows. The charge materials are fed into the receiving funnel 11 with the airlock chamber “z” open at the top. After filling the next portion of the charge, the drive 15 is closed by the drive 15 with the cone 14 and the camera inlet is opened by the drive 16 and the output hole previously closed by the return cone 14 is opened. The charge falls into the funnel 12 and then into the tank "a", where it is heated by passing current through the current lead 4, graphite tube 3. Due to the high temperature of the heater, the heater graphite interacts with atmospheric oxygen to form carbon monoxide, which creates a reducing atmosphere inside and outside the heaters a. During heating and melting of a charge, its components interact with atmospheric carbon and carbon of heaters, resulting in the reduction of a metal, for example, iron from iron ore. The reduction reactions proceed in this case very intensively, because the influence of the reducing agent and heat generation are concentrated in a small volume and intensified by magnetic fields. The metal formed during melting flows through the channels "d" and when the shut-off device 6 is open, through the sleeve 17 it enters the tank "b", bounded on the outside by the lining 2 and the housing 1 and heated by the external contour of the pipes 3. The furnace gases are discharged through the manifold 10. Required the melt level in the tank "a" is supported by the height of the sleeve 17.

 To reduce the carburization of the metal from the lining and reduce wear under the furnace 5 can be protected by a skull.

 As the melt progresses, metal builds up in the lower part of vessel "a", and then in vessel "b". Slag, as a lighter component of the melt, accumulates in the tank "a". After the accumulation of the required amount of metal, the latter through the channel "g" after opening the shut-off device 6a is passed into the tank "in". This container is lined with carbon-free material, therefore it is possible to carry out decarburization operations by introducing an oxidizing agent. A plasma torch can be used to maintain temperature. By supplying nitrogen, nitriding can be performed, or other types of processing of liquid metal. After bringing the metal to the desired composition, the latter is released through the casting channel "e" into the casting ladle. After the metal is drained into the tank “into”, the channel “g” is closed and the slag remaining in the furnace is drained through the channel system into the tank “g” of the slag carrier 9.

 The charge is reloaded into the furnace and the cycle repeats.

 The technical result from the application of the claimed design is the stabilization of the temperature regime of the melting course, due to the maintenance of constant resistance of the fuel element.

Claims (3)

 1. An electric resistance furnace for smelting steel from an iron ore charge, comprising a thermally insulated body lined with refractory, underneath, a graphite heater with current supply devices located in the inner cavity of the lined body, a melting space and a loading device connected to the melting space, characterized in that under is made of graphite, a graphite heater made in the form of a pipe rests on under, the melting space is formed by the inner surface of the graphite heater and a hearth and is connected by a hearth channel equipped with shutoff valves, with a capacity for accumulating and heating cast iron, which is limited by the inner surface of the graphite heater and a hearth, the latter tank being connected by a channel with shutoff valves to a tank for refining and finishing metal, limited by the refractory lining of the furnace body.  2. The electric furnace according to claim 1, characterized in that several tubular graphite heaters are installed inside the furnace body with a multiple of three, included in the power circuit to a "star", and underneath closes the heaters from below, phase conductors are connected to the top of the heaters, and the neutral conductor attached to the hearth of the furnace.  3. An electric furnace according to claim 1, characterized in that the metal refining and lapping tank is sealed and equipped with a plasma installation for heating and supplying oxygen, refining and alloying additives.

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