RU2086871C1 - Method for protection of lining of arc steel melting furnace - Google Patents

Abstract

FIELD: ferrous metallurgy; arc steel melting surfaces. SUBSTANCE: powder-like limestone flux is fed to zone of electric arcs and to under-hearth space at an angle of 10-20 deg relative to level in flow of gas jets. For realization of this method, use is made of powder-like mixture on base of limestone with particles not exceeding 0.5 mm at content of 0.1-mm fraction of no less than 70%. Blast is started when temperature of metal reaches 1300-1400 C and is continued during entire period of striking of arcs in way of melt. Intensity of flux supply is maintained within 0.3-0.8 kg/t.min. EFFECT: increased resistance of arch and stabilizing of striking of arcs. 1 dwg, 1 tbl

Description

 The invention relates to ferrous metallurgy, to the production of steel and alloys in electric arc furnaces.

 A known method of protecting the lining of the furnace from the emission of arcs by installing inside the furnace ring refractory screens / 1 /. The main disadvantages of this method of shielding should include its complexity and low technology, because it is necessary to organize the production of such rings, and installing them in the melting space will increase the melting time, and also extremely complicate the introduction of materials into the furnace and work with slag.

 There is also a method of protecting the lining from the emission of arcs, providing for shielding by supplying steam to the area of the arcs / 2 /.

 However, this method leads to a useless increase in energy consumption for heating and decomposition of water vapor. Inevitably, the saturation of the metal with the decomposition product of hydrogen; the presence of the latter in the furnace atmosphere also creates an explosion hazard. These disadvantages make this method practically unsuitable for implementation on electric arc furnaces.

 The closest to the achieved result is a method of steelmaking in an electric arc furnace, including shielding the lining from the effects of electric arcs by continuously feeding limestone flux into the working space of the furnace / 3 /. However, this method has drawbacks - delayed slag formation due to the extended supply of flux in pieces, which in this form is also not able to effectively shield the radiation of arcs.

 The proposed method is devoid of these disadvantages.

 The aim of the invention is to increase the durability of the lining of the roof and the underwater space of the furnace, as well as stabilizing the burning of electric arcs and reducing noise.

This goal is achieved in that the limestone flux in powder form is directed in a stream of gas jets into the zone of electric arcs and into the underwater space of the furnace at an angle of 10-20 ^o to the horizontal, while the flux supply intensity is maintained within 0.3-0.8 kg / t • min, and the particle size of the limestone flux is not more than 0.5 mm with a fraction of 0.1 mm not less than 70
The invention meets the conditions of patentability: it has novelty, has an inventive step, because explicitly does not follow from the existing level of technology and does not cause technological difficulties when implemented in industry.

 The method is illustrated by the attached diagram, see drawing.

 The method is illustrated by the following.

Flux injection is carried out during periods of arc burning. Limestone or flux based on it should have a particle size of not more than 0.5 mm with a fraction content of 0.1 mm of not less than 70. Such a particle size distribution ensures the formation of an effectively shielding dust cloud in the furnace. One dust and gas stream is directed into the zone of electric arcs, creating the first dust screen. In addition, the presence of calcium compounds in this zone provides a more stable burning of arcs, which means it increases the electrical efficiency of the furnace. Two other dust and gas jets direct to the arch at an angle of 10-20 ^o to the horizon. A minimum angle of 10 ^{o is} necessary for sufficient range of the jet; increasing the angle above 20 ^o can lead to mechanical damage to the lining of the arch when touching its stream.

 The intensity of flux injection should be a total of 0.3-0.8 kg / t • min (0.3-0.8 kg / t • min, this amount of flux is supplied in 1 min for every 1 ton of metal). A lower intensity limit of 0.3 kg / t • min is necessary to ensure a sufficient shielding effect. At an intensity of more than 0.8 kg / t • min, an excess amount of slag is formed in the furnace, and also the dust content of the gases released from the furnace increases.

In addition to shielding, dust and gas jets containing limestone protect the lining from overheating due to the development of an endothermic limestone decomposition reaction:
CaCO ₃ CaO + CO ₂ ;
ΔH $\genfrac{}{}{0ex}{}{\text{o}}{\text{298}}$ = 178 kJ.
Fine particles of CaO and CaCO ₃ , settling on the surface of the bath, ensure the rapid formation of active refining slag. This contributes to the effective removal of impurities from the metal of phosphorus and sulfur.

 In addition, there is no need for calcining limestone in special calcareous kilns, as this process takes place directly in the steelmaking electric furnace.

 The method is as follows.

A reduced amount of slag-forming substances is given into the filling and, after turning on the furnace, limestone flux is blown in using three lances. The intensity of injection should be increased to a maximum after the melting of most of the mixture and reaching a temperature of 1300-1400 ^o C.

One lance directs the jet into the zone of electric arcs, and the other two - up into the underwater space. Forms must be movable to set the optimal angle within 10-20 ^o to the horizon. Up to 20 materials such as coke, chamotte, fluorspar, etc. can be added to the limestone.

 The blowing intensity in the range of 0.3-0.8 kg / t • min, as well as the concentration of the powder in the carrier gas is regulated by valves on the pneumatic box.

 The flux is blown into the energy and technological periods with burning arcs, preventing the overheating of the arch, the temperature of which is constantly monitored by a thermal probe. When the oven is turned off, the purge stops.

 Testing the method in a laboratory arc furnace showed a high cooling effect of the gas-powder jet.

The test results presented in table. 1, allow us to establish the following: the range of the jet increases with an increase in the angle of inclination from 5 to 25 ^o , and an increase in the angle in excess of 20 ^o no longer causes a significant elongation of the jet, which at the same time starts to touch the arch; with an increase in the intensity of injection from 0.3 to 1 kg / t • min and with an increase in the fraction of the fraction less than 0.1 mm from 50 to 80, cooling of the arch improves, and the decrease in its temperature is instead of 40 ^o already 47-55 ^o .

 Part of the kilns at the factory should be replaced by grinding equipment to obtain powdered limestone. Screening of calcareous kilns can also be used.

 It is also important that for the purposes of steelmaking it becomes possible to use deposits of brittle, crumbly limestone, which are usually not exploited.

 Injection of limestone stabilized the burning of arcs, which in experimental melts was manifested in a decrease in the noise level from an arc discharge. This eliminates the most harmful high tones.

 It has been established that during the time of soaking in the furnace, limestone particles decompose to lime by about 70 V in an industrial furnace, where the time of soaring of particles in the gas phase is much longer, the degree of limestone dissociation should be close to 100

Claims (1)

A method of protecting the lining of an electric arc furnace from overheating, comprising supplying limestone flux to the furnace working space, characterized in that the flux in powder form is directed in the stream of gas jets into the area of electric arcs and into the underwater space at an angle of 10 - 20 ^o to the horizontal, the flux supply intensity is maintained within the range of 0.3 ^o C 0.8 kg / t min, and the particle size of the limestone flux is not more than 0.5 mm with a fraction of 0.1 mm of not less than 70%

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