SU1482956A1 - Method of blasting the bath with oxigen in oscillating open-hearth furnace - Google Patents

Abstract

The invention relates to ferrous metallurgy and solves the problem of increasing the productivity of rolling steel-smelting units operating on high-phosphorus pig iron. The purpose of the invention is to increase productivity by synchronizing the decarburization and deformation processes. The essence of the method is that, starting from the moment lime build up and ending when the metal temperature reaches 1500-1560 ° C, during the second period of scrap melting, oxygen jets are introduced below the metal level periodically with a frequency of 1-4 cycles per hour, and the duration Blowing under the level is 50-80% of the cycle time, and for the remaining 20-50% of the cycle time, oxygen is supplied to the slag-metal interface. This technology ensures the synchronization of the processes of oxidation of carbon and phosphorus, which ensures an increase in the productivity of the steel-smelting unit by an average of 4 tons per hour. 1 tab.

Description

The invention relates to ferrous metallurgy, in particular to the production of steel in the bottom steel-smelting units during the redistribution of high-phosphorus pig iron.

The purpose of the invention is to increase productivity by synchronizing the processes of decarburization and de-phosphorization.

The essence of the method is as follows. The beginning of the second period of the metal melting in the open-hearth furnace is characterized by lime rising in the melt

At the moment lime starts to rise, the viscosity of the furnace slag rises sharply. At the same time, slag acquires a heterogeneous structure. Under the conditions of a deep purge with oxygen, when oxygen jets are supplied below the metal level, these phenomena are aggravated by the low content of iron oxides in the slag.

As a result of these processes, the oxidation of phosphorus significantly lags behind the oxidation of carbon, which leads to the need to increase the duration of the finishing melting and reduce the productivity of the furnace. The alternate introduction of oxygen jets to the slag – metal interface and under the metal level allows

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to carry out intensive decarburization of the metal with a high content of iron oxides in the furnace slag, which ensures optimal thermodynamic and kinetic conditions of metal dephosphorization. An increase in the content of iron oxides in the slag is provided when oxygen jets are introduced at the slag-metal interface. The high content of iron oxides in the slag contributes to the rapid dissolution of lime, a decrease in the viscosity of the slag, an increase in the oxidizing potential of the slag, which, together with the high basicity of the slag, leads to an increase in the rate of metal dephosphorization. At the same time, when oxygen jets are fed alternately below the metal level and at the slag-metal interface, the oxidation rate of carbon decreases somewhat, which leads to almost simultaneous production of specified concentrations of carbon and phosphorus in the metal before the melting

In the case of the onset of periodic displacements of oxygen jets before lime build-up, the rate of carbon oxidation decreases without a noticeable increase in the metal's dephosphorization rate, which is due to the low basicity of the slag during this period. At the same time, the finishing time is increased due to the need to remove excess carbon when the required phosphorus content in the metal is reached, and an increase in the finishing time leads to a decrease in furnace productivity.

In the case of the onset of periodic displacements of oxygen jets after lime build-up, the metal decarburization process is ahead of its dephosphorization, which leads to an increase in the finishing time due to the need to remove excess phosphorus content in the metal and a decrease in furnace productivity.

Thus, the best option for the onset of periodic movements of oxygen jets is the moment lime occurs.

When the frequency of the introduction of oxygen jets below the metal level less than one cycle per hour, the oxidation of carbon and phosphorus is not synchronized, since the oxidation of phosphorus lags behind the oxidation of carbon following

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effect of low slag oxidation. With a frequency of introducing oxygen jets below the metal level for more than four cycles per hour, the oxidation rate of phosphorus in the metal exceeds the oxidation rate of carbon. In both cases, the furnace productivity decreases due to an increase in the duration of the finishing operation, caused in the first case by the need to oxidize excess phosphorus in the metal, and in the stunt case, the excess carbon in the metal.

The cycle of the periodic injection of oxygen jets under the metal level consists of the following phases: purging with oxygen under the metal level; moving the jets on the border of the slag - metal-, blowing on the border of the slag - metal, moving the jets under the metal level.

The duration of the movement of the oxygen jets enters the duration of the purge below the level, since at this time the purge does not stop. Thus, the cycle of moving oxygen jets consists of two phases: oxygen blowing under the level and oxygen blowing at the slag-metal interface.

With a purge duration under the metal level of 50% of the cycle duration, the oxidation of carbon lags behind the dephosphorization of the metal, and with a duration of more than 80% of the duration of the phosphorus oxidation cycle, it lags behind the oxidation of carbon. In both cases, the capacity of the furnace is reduced. The same applies to the duration of the blowdown at the border of the slag - metal not less than 20% and more than 50%.

Example. VstZsp steel is smelted in a 400-ton swing open-hearth furnace using a scrap process. In the rear wall of the furnace, 14 oxygen tuyeres are installed, through which oxygen is supplied with a total flow rate of 1200 and protective gases — argon (200 m / h) and natural gas (400). After the cast iron is cast, the furnace is tilted towards the rear wall, while the tuyeres are immersed in the melt to a depth of 200 mm. In the course of melting, the inclination of the furnace periodically changes, with the oxygen jets introduced into the melt moving to the slag-to-metal interface or below the metal level. In the course of research, the time of the beginning and end of the periodic rocking of the furnace (movement of oxygen jets), the frequency of change of the point of entry of oxygen jets (below the metal level and at the metal-slag boundary) and the duration of the blow under the metal level and at the metal-slag boundary are changed. The remaining technological parameters are kept approximately constant. The heat mode of the furnace corresponds to the heat engineering instruction, the iron consumption is 280 tons, scrap metal - 100 tons, iron ore - 80 tons, limestone - 40 tons, and up to 16 tons of lime are placed in the furnace during the period of refining.

The parameters by which the efficiency of blowdown with different operating parameters is estimated are the actual phosphorus content in the metal with the average carbon content in the metal before production and the furnace productivity, t / h.

Conducted three series of experienced swimming trunks.

In the first series, the periodic injection of oxygen jets under the level of the metal and on the metal-ishak border began before lime began, the second from the moment lime rose, and in the third 10 minutes after lime began. The results of the experimental heats are presented in the table. The numerator shows the actual phosphorus content in the metal with the average carbon content in the metal, in the denominator - the furnace productivity (t / h).

During steelmaking under the same conditions using the prototype technology, the furnace productivity is 40.0 t / h, the oxidation of carbon is significantly ahead of the dephosphorization, which

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leads to the need to increase the duration of refinement.

A statistical analysis of the results of industrial melts carried out during the redistribution of high-phosphorus iron in swinging open-hearth furnaces showed that, all other things being equal, the furnace performance is determined by the length of the refining period, which in turn depends on the degree of synchronization of carbon and phosphorus oxidation processes in the metal. The minimum finishing time and maximum furnace productivity are achieved subject to the simultaneous production of predetermined concentrations of phosphorus and carbon in the metal before the release of the heat.

Thus, the synchronization of the decarburization and dephosphorization processes provides an increase in the furnace productivity of 4 t / h.

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Claims (1)

Invention Formula A method of purging the bath with oxygen in a swinging open-hearth furnace, including the supply of oxygen to the bath through tuyeres installed in the rear wall of the furnace in the first and second melting period, characterized in that, in order to increase productivity by synchronizing the decarburization and defoscopy processes, oxygen in the second melting period, periodically served under the level of the melt and at the metal-slag interface with a frequency of 1-4 periods of 1 h, and the duration of oxygen supply under the level is 50-80% of the duration of ne Rhoda.