RU2449026C1 - Melting method of iron-carbon by-product in other steel making furnace - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to ferrous metallurgy and can be used during manufacture of iron-carbon by-product in arc-type steel-making furnace (ASF) of high specific power for further melt processing at furnace-ladle facility. Method involves preparation and supply of the charge containing carbon-bearing material (CBM), metal junk and lime, its melting in ASF bath so that iron-carbon by-product is obtained and hot metal is tapped to steel-pouring ladle. At that, CBM amount is specified depending on the carbon amount required for melting of iron-carbon byproduct, which is calculated depending on bath boiling duration and carbon oxidation rate during melting process.

EFFECT: invention allows reducing CBM consumption specified during melting and charging by 1-3 kg/t of metal junk and thus reducing the melting process duration and specific electric power consumption by 4 kW·h/t.

2 tbl, 1 dwg

Description

The invention can be used in ferrous metallurgy in the production of iron-carbon melt in an arc steelmaking furnace (DSP) of high specific power for subsequent processing on a ladle-furnace (ACP) unit.

At present, in domestic and foreign part-time metallurgical factories (mini-factories) for the smelting of iron-carbon melt (intermediate) used for the production of steel on automatic gearboxes, chipboards are used, the specific power of which is 0.8-1.0 MVA / t and above, while most of the technological operations are carried out from the furnace to maximize the use of the power of the electric furnace transformer. Carbon-containing materials (USM) and lime are added to the chipboard mixture in order to organize the boiling of the metal bath during oxygen purging and early slag formation, which makes it possible to combine the energy and oxidation periods of smelting to a large extent, and, thanks to the use of ACP, it is possible to release the intermediate from the chipboard immediately after the melting of the scrap and overheating of the melt to the desired temperature. Boiling a chipboard bath allows you to achieve:

- homogenization of the melt in temperature and chemical composition;

- degassing to remove hydrogen and nitrogen from the melt;

- increase the surface of the interaction of metal and slag to intensify the processes of oxidation of impurities and the assimilation of non-metallic inclusions in the slag.

After the metal is discharged from a modern chipboard, it is subjected to inert gas purging at the ACP, which makes it possible to fully degass and remove non-metallic inclusions from steel outside the furnace; therefore, the carbon in the charge of a modern chipboard should be sufficient to ensure boiling of the metal during melting after the appearance of a liquid bath and until the end of the smelting, but not more than this amount, it can accelerate the dissolution and melting of scrap in a liquid bath due to intensive mixing of the melt and reduce the consumption of USM and acid kind.

A known method of producing a melt in a chipboard by melting steel scrap with full oxidation for subsequent processing of metal in a ladle, in which coke, cast iron or electrode fight is used to charge carbon melting, based on the calculation that from 0.3 to 0.5% carbon. For large furnaces, these amounts can be slightly reduced. The oxidation of this amount of carbon is required for metal degassing. To fulfill this condition, the carbon content in the charge should be 0.3-0.5% higher than the lower limit in steel of a given grade [see, for example, Povolotsky D.Ya., Roshchin V.E., Ryss M.A. et al. Electrometallurgy of steel and ferroalloys: a Textbook for high schools. Ed. 2nd, rev. and add. - M .: Metallurgy, 1984, S. 341-365].

When calculating the charge according to the specified method, the capacity of the chipboard and its equipment with means for the intensification of smelting are not taken into account by parameters that significantly affect the rate of carbon oxidation. This can lead to an increase in oxygen consumption, USM, melting time and, as a result, a decrease in productivity and yield.

Also known are methods of smelting iron-carbon intermediate in particleboard with a capacity of 100-150 tons for subsequent processing on automatic gearboxes, which consist in the melting of steel scrap or metallized pellets with the addition of USM in the loading basket in an amount of 7 to 20 kg / t [see, for example, 1 ) A. Pujadas, J. McCauley, M. Iacuzzi. EAF Energy Optimization at Nucor-Yamato Steel // Iron and Steel Technology. July. 2004. P. 104-112. English .; 2) A. Faessel, J.L. Roth. The Use of Coal in the EAF // Revue de Metallurgie-CIT. 1996. No. LP. 69-73. English .; 3) Kabluka V.V., Kulakov V.V., Matus V.M. et al. Implementation of the melting intensification system in DSP-100 ESPTs Ural Steel LLC // Metallurg. 2005. No9. S.56-57].

The disadvantage of these technologies is that the calculations do not take into account the carbon contained in the metal part of the charge, and the duration of the boiling bath. In this case, with an excess of carbon, the melting time increases due to the need to oxidize it, with a lack of carbon it can increase the energy consumption due to insufficient mixing of the bath, and when the carbon content in the melt is less than 0.1%, intense oxidation of iron begins, which reduces the yield of metal .

The technical result from the use of the proposed method is to reduce the duration of the smelting of iron-carbon intermediate in the chipboard, reducing the consumption of carbon-containing materials (USM) specified in the chipboard during melting and blending, and oxygen consumption for decarburization.

The technical result is achieved by determining the required technologically justified amount of USM before the start of smelting, depending on the duration of boiling the metal bath, smelting mass, decarburization rate and technology for the production of iron-carbon intermediate.

The calculated amount of carbon is added in the form of coke, anthracite, cast iron or electrode fight, during the filling of chipboard, in the first loading basket. Smelting is carried out according to one-slag technology with full oxidation. The mixture is composed of carbon scrap, USM and lime. Oxygen burners are used as a means of melting intensification in particleboard in the initial period of charge melting, oxygen purging after the appearance of a liquid bath, and blowing of a powdered trigger for foaming slag. After melting the entire loaded charge, the melt is adjusted in temperature and chemical composition. At the end of production, a liquid residue (“swamp”) is left in the furnace in an amount of 10-15% of the chipboard capacity.

A diagram of the process of production of iron-carbon melt in the chipboard for subsequent processing on the automatic gearbox is presented in figure 1.

The proposed method consists in the preparation and filling of a charge containing a carbon-containing material (USM), scrap and lime, its melting in a chipboard bath to obtain an iron-carbon intermediate and the release of heat in a steel-pouring ladle, while the amount of USM is set depending on the amount of carbon (C _d ), kg, necessary for the smelting of iron-carbon intermediate, calculated depending on the duration of the boiling bath and the oxidation rate of carbon during the smelting process in the ratio

where τ _to - the duration of the boiling bath, min;

V _ok - the average melting rate of carbon oxidation, kg / min;

[With _{p / p} ] - the required carbon content in the intermediate product,%;

[With _{p / p0} ] is the carbon content in the intermediate of the previous heat,%;

[C _w ] - carbon content in the chipboard scrap,%;

G _b , G _b0 - mass of liquid residue at the outlet of the heat and the previous heat, kg;

G _p - the mass of heat, kg;

To _p - coefficient of consumption of scrap.

As a rule, during the serial operation of chipboard, the carbon content in the intermediate from smelting to smelting changes insignificantly, therefore it is advisable to take [С _{п / п} ] ≈ [С _{п / п0} ], which allows us to simplify the ratio (1):

The duration of the boiling bath can be measured on the existing chipboard by monitoring the progress of the heat. The duration of the boiling of the bath can also be estimated by the relation (2), taking into account that the boiling process begins some time after the bath is purged with oxygen. Purge begins, usually after the appearance of a liquid bath.

where τ _e , τ _t - the duration of the periods of melting, respectively, energy and technological, min;

To _to - a coefficient depending on the duration of the boil, 0 ... 1.

The coefficient K _{k is} chosen from 0 to 1, depending on the duration of the boiling bath.

Given the features of modern technology, we can take (τ _e + τ _t ) = τ _e .

The duration of the energy period of the heat can be determined from the following ratio.

where W _{e / e} - power consumption for melting, kW · h;

S _n - rated power of the transformer, MVA;

cosφ is the power factor;

To _them is the coefficient of utilization of the rated power of the transformer.

As an example of the method, the technologically justified amount of carbon required for smelting the iron-carbon intermediate was calculated in a chipboard with a capacity of 35 tons of the State Unitary Enterprise "Foundry-rolling plant", Yartsevo (LPZ).

The product (cosφ · K _nm ) for a chipboard with a capacity of 35 tons, according to the results of processing production data, is 0.81, and the average carbon oxidation rate is 0.02% / min, which corresponds to a mass decarburization rate of 7 kg / min (V _ok ).

The energy consumption for melting in DSP-35 is on average 15.2 MW · h (W _{e / e} ); the furnace is powered by an electric furnace transformer with a rated power of 25 MBA (S _n ). The duration of the energy period was calculated by the ratio (3)

Assuming that the oxygen purge at LPZ start of melting of about 50% scrap factor K equal _to 0.5.

Therefore, the duration of the boiling bath, according to expression (2), will be

τ _k = 45 · 0.5 = 22.5 min.

The decarburization rate, as indicated above, is about 7 kg / min. According to production data, the mass of the melt at the outlet is about 33 tons (G _p ), the scrap consumption rate is about 1.07 (K _p ). Given that the mass of the “swamp” from melting to melting differs insignificantly, and also that the concentration of carbon in the “intermediate” at the outlet is usually about 0.1%, and in the carbon scrap - about 0.3%, according to the ratio (1.1 ) determined the amount of carbon needed for melting.

Thus, about 4.4 kg / t of pure carbon must be added to the chipboard DSP-35.

To confirm the technical result, more than 70 experimental swimming trunks were carried out in the chipboard. When conducting experiments, the required content of the USM in the mixture was determined by the expression (1.1). Lump graphite in the amount of 4.0-5.0 kg / t of loaded scrap was used as a trigger for all melts. In addition to the USM, carbonaceous scrap and lime in an amount of about 35 kg / t of scrap were loaded into the furnace before melting.

The average performance of DSP-35 LPZ during experimental swimming trunks is presented in Table 1.

Tab. one The average performance of DSP-35 State Unitary Enterprise "Foundry-rolling plant", Yartsevo, during the experimental melting Indicator (specific - per t of "intermediate") Value Specific energy consumption, kW · h / t 445 Specific oxygen consumption, m ³ / t 17.4 Duration of work under current, min 44.1 Melting time, min 64.1 Specific consumption of natural gas, m ³ / t 3.0

For comparison, the average values of the performance indicators of DSP-35 LPZ are given (Table 2). For most of the melts analyzed, 6–7 kg / t USM in the form of lump graphite and 35–40 kg / t lime were added to the chipboard mixture.

Tab. 2 Average performance of DSP-35 State Unitary Enterprise "Foundry-rolling plant", Yartsevo (results for May and October 2009) Indicator (specific - per t of "intermediate") Value Specific energy consumption, kW · h / t 449 Specific oxygen consumption, m ³ / t 18.0 Duration of work under current, min 44.5 Melting time, min 66.5 Specific consumption of natural gas, m ³ / t 3.0

Thus, the application of the method allows to reduce the duration of melting for a time of about 2.4 minutes, specific energy consumption by 4 kW · h / t, USM consumption by 1-3 kg / t of scrap, oxygen consumption by 0.6 m ³ / t intermediate. At the same time, in experimental swimming trunks, there was no increase in energy consumption and duration of operation “under current” due to a decrease in the incoming part of the heat balance due to a decrease in the mass of carbon in the filling.

Claims (1)

A method for smelting an iron-carbon intermediate in an arc steel-smelting furnace (DSP) for subsequent processing on a ladle-furnace (ACP) unit, including the preparation and filling of a charge containing carbon-containing material (USM), scrap and lime, its melting in a DSP bathtub to produce an iron-carbon intermediate and the production of melting in a steel pouring ladle, characterized in that the number of USM is set depending on the amount of carbon, (C _d ), kg, necessary for the smelting of the iron-carbon intermediate calculated in the dependent depending on the duration of the boiling bath and the rate of carbon oxidation during smelting, according to the ratio

where τ _to - the duration of the boiling bath, min;
V _ok - the average melting rate of carbon oxidation, kg / min;
[With _{p / p} ] - the required carbon content in the intermediate product,%;
[With _{p / p0} ] is the carbon content in the intermediate of the previous heat,%;
[C _w ] - carbon content in scrap,%;
G _b , G _b0 - mass of liquid residue at the outlet of the heat and the previous heat, respectively, kg;
G _p - the mass of heat, kg;
To _p - coefficient of consumption of scrap.

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