SU1750433A3 - Method of blasting melt in bottoms steel smelting unit - Google Patents

Abstract

Usage: in the steel industry. An increase in the productivity of the hearth steelmaking unit is achieved by optimizing the position of the tuyere (F) in the course of finishing (D). SUMMARY OF THE INVENTION: The first 20-40% of the duration of period D is purged when the nozzles Φ are located above the metal-slag (M – W) interface at a distance of 6–8 given calibers (PC). The nozzles F are then installed at the interface of the M-III, the content of iron oxides in the slag is measured and blown with oxygen until 50-70% of the iron oxides are reduced from the slag, after which the blowdown is carried out at the position of the nozzles F at a distance of 2-4 pcs above the boundary section m-sh. 1 hp ff, 2 tab.

Description

The invention relates to ferrous metallurgy, in particular, to methods for melt blowing in open-hearth furnaces and double-bath steel-making units, and can be used in steelmaking in electric furnaces.

There is a method of purging the melt with oxygen through multi-nozzle lances immersed to the metal-slag interface (M-W) or into the metal.

The disadvantage of this method is a decrease in the yield of the liquid metal due to the constant position of the tuyere during the purge.

There is also known a method of purging the melt with oxygen with a variable position of the tuyere along the course of the purge.

However, the incomplete use of the possibilities of intensification of the process

the use of gaseous oxygen does not allow for maximum performance of the unit at a given oxygen consumption.

The closest to the claimed technical essence and the achieved result is a method of smelting high carbon steel in a two-bath furnace, including blowing metal with buried oxygen, heating of slag with oxygen-oxygen burners and preliminary deoxidation of metal, and during carbon 0.2-0.4% above the average decay in the finished steel 20-30% of the oxygen consumed for purging is served above the slag surface

However, the method does not provide the maximum performance of the unit at a given oxygen consumption.

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The aim of the invention is to increase the productivity of a steelmaking unit by reducing the length of the finishing period.

The goal is achieved by the fact that according to the method of melt blowing in the bottom steelmaking unit, which includes supplying gaseous oxygen through arched water cooled tuyeres during the periods of blowing and finishing to the M-Sh interface, raising the tuyeres during the finishing period above the M-Sh interface, conducting a winding period , in the first 20-40% of the period of completion, the purging is carried out when the nozzles of the tuyeres are located above the M-Sh boundary at a distance of 6-8 given calibers, then the tuyere nozzles are installed at the M-Sh interface The content of iron oxides in the slag is measured and purged with oxygen until 50-70% of the iron oxides are reduced from the slag, after which the purge is carried out with the position of the tuyere nozzles at a distance of 2–4 given calibers above the M-III interface, and during the melting are the boundary of the section M-Sh.

In order to successfully carry out slag formation processes that determine the duration of finishing, it is necessary to satisfy two conditions: the presence of active solvents of lime in the slag and the high temperature of the metal and slag. The solution of these problems is achieved by immersing the tuyere in the slag, i.e. its location above the boundary of the section M-Sh. The result of this effect is the intense oxidation of iron, accompanied by a rapid rise in temperature and slag saturation with iron oxides. In this case, rapid dissolution of lime is achieved, and at the beginning of the finishing operation, an active homogeneous slag is formed, which has a high desulfurization and dephosphorizing potential. However, in carrying out this operation for less than 20% of the duration of refining, the processes of heating and slag saturation with iron oxides are not sufficiently accelerated to noticeably increase the productivity of the unit. When performing this operation for more than 40% of the time spent on refining, overheating of the bath and the high content of iron oxides in the slag lead to the release of metal and slag from the furnace, which makes it necessary to reduce the heat load, stop the blowing, cool down the bath and eventually furnace performance. When the tuyere is positioned less than b of the above calibers of oxygen nozzles above the M – W limit, the bath heating acceleration is practically not observed, and when it is raised to a height of more than 8 of the calibers, the use of iron oxidation heat to heat the metal decreases, which is caused by the intensive dispersion of slag and removing it from the working space of the furnace. In both cases, the capacity of the unit is reduced,

0 After the termination of the first period of finishing, carried out at the high position of the tuyere, the bath is prepared for the main finishing period, i.e. active slag formed and provided

5 high metal temperature. To realize the advantages achieved at the beginning of the refinement, the tuyere is lowered onto the M-Sh boundary. At the same time, due to the high temperature of the metal, the rate of oxidation of carbon increases, which leads to intensive mixing of the bath, improvement of its heating by heat of the plume, acceleration of the processes of refining from harmful impurities. In this way, all major processes are accelerated. flowing in the bath: heating, desulfurization and dephosphorization, carbon oxidation, which is a decisive condition for increasing the productivity of the unit. However, the forcing of these processes is observed only in a limited period of refinement, which in each case is determined by the decrease in the content of iron oxides in the slag. With continued purging through tuyeres located at

5 at the interface of the M-III, after the content of iron oxides decreases by more than 70% of their content at the time of the tuyeres immersion at the interface, the mixing of metal and slag in significant

The degree of retardation is due to a decrease in the intensity of the oxidation of carbon at the boundary between the metal and the slag, which occurs due to the oxygen contained in the iron oxides.

five

This slows down the refining processes, complicates the transfer of heat and atmospheric oxygen to the metal through the slag and leads to a decrease in the productivity of the furnace.

Upon termination of the blowdown at the interface of the М-Ш, before the reduction of 50% of iron oxides contained in the slag at the time of immersion, the potential accumulated by the bath during the first period of refining, i.e. the processes of stirring, heating, de-shaping and removing carbon are still intense, and the tuyeres are raised, reducing the intensity of carbon oxidation and mixing

This leads to a loss of productivity of the unit.

After the slag oxidation decreases and the slag bath boils down, it is necessary to intensify this process, which is the basis for rapid refining and bath heating; This is achieved by re-raising the tuyere over the M-Sh boundary. In this final period of finishing, the bath is already sufficiently heated, and to oxidize carbon there is no need to blow oxygen directly into the metal. The process is stable due to the transfer of atmospheric oxygen, oxygen dissolved in the metal, and blown oxygen passing through the slag, passing into the metal through the slag. When the tuyeres are raised in the third period of fine-tuning by less than 2 calibrations of oxygen nozzles, the under-slag boiling of the bath is not intensified, and when the tuyere is raised to a height of more than 4 calibers, excess iron oxides enter the slag, which thermodynamically inhibits desulfurization. In addition, this reduces the rate of oxidation of carbon by reducing the efficiency of direct interaction of the oxygen jets with the liquid metal. In both cases, the productivity of the unit decreases.

An illustration of the above scheme is the timing of two heats held in a 300-ton open-hearth furnace using the proposed () and known (II) methods (Table 1).

Example. Steel of grade B, the St of ZSP was smelted in a 300-ton open-hearth furnace, which operates a scrap ore process with an oxygen bath blowing. After the previous smelting was completed, scrap was filled (150 tons), lime was charged (18 tons), the charge was heated for 40 minutes, molten iron was poured (180 tons) and oxygen purging was started at 3000 m / h after three six-water water cooled tuyeres with a nozzle diameter of 12 mm (the reduced nozzle diameter is 29.4 mm). The heat regime of the furnace during the pilot heats corresponded to the instructions and did not change from melting to melting. Blowing started immediately after cast iron was cast, lowering the tuyere as the charge melted to the border of the section MW, Complete melting of the bath was recorded visually by stopping the spouting of the metal at the sites of non-melted scrap metal. When carrying out the bottoms of the proposed method at the time of termination

the spouting of the metal (i.e., at the moment of the start of finishing) the tuyeres were raised above the boundary of the М-Ш section to a certain height and held in this position for some 5 times, then lowered onto the interface and the tuyeres were raised again at the end of the finishing.

When conducting melting as in the prototype, tuyeres were at the interface

0 M-Sh throughout the refinement.

The position of the M – III boundary was determined by the electrocontact method, for which one of the tuyeres was isolated from the metalwork. An ohmmeter was installed between the isolated tuyere and the metal structures. When the tuyere was in the furnace atmosphere, the resistance in the chain of the tuyere metal structure was 140000-350000 Ohm.

0 When the tuyere was in the slag, the resistance was 150-230 Ohm (the circuit was closed through the slag). When the lance hit the metal, the resistance was 2–7 Ω (the circuit was closed 1 through the metal). Co5 supplied a diagram of the movement of the tuyere with sharp fractures in the resistance diagram, determined the position of the M-Sh interface. Then, the selsyn was used to install all the tuyeres in the desired position. Taking into account the fact that the position of the M-Sh boundary during the smelting changes somewhat, the determination of the position of the boundary was made every 7 minutes, making, if necessary, Adjustments to the tuyeres position.

5 Accuracy of installation of tuyeres + 1 cm.

The efficiency of the purge method was estimated by the finishing time, which was determined from the moment the metal flow was stopped (the end of

0) until the temperature of the metal reaches 1620 ° C, the carbon content is 0.2%, and the phosphorus content is 0.025%.

At the moment when all the above parameters reached the required values (the blower was stopped, the metal was aged in the furnace for 10 minutes (non-purge period for self-depletion of the bath) and the metal was released into the ladle, where it was deoxidized. In all cases

0 steel was assigned according to GOST 380-71 without limitation of use,

Table 2 shows the results of the experimental heats using the proposed and known methods of melt blowing,

5 of which during the whole refinement of the tuyere were located on the border of the section M-Sh.

Thus, the implementation of the proposed method with simultaneous hit of all its parameters in the proposed limits provides a significant increase in the performance of the unit by reducing the length of the adjustment.

Claims (2)

Claim 1. Method of melt blowing in the bottom steel-making unit, including supplying gaseous oxygen through the water-cooled tuyeres during the periods of blowing and finishing at the metal-slag interface, raising the tuyeres during the finishing period above the metal-slag interface, conducting a sweep period, that, in order to increase the productivity of the furnace by reducing the length of the refining period, five The first 20-40% of the finishing time period is carried out at the position of the tuyere nozzles above the metal-slag interface at a distance of 6-8 given calibers, then the tuyere nozzles are installed at the metal-slag interface, the content of iron oxides in the slag is measured and blown with oxygen until 50–70% of iron oxides are reduced from slag, after which the purge is carried out with the position of the tuyere nozzles at a distance of 2–4 given calibers above the metal – slag interface. 2. Method pop. 1, characterized in that the metal-slag interface is defined along the smelting. Table I Table