RU2388832C2 - Procedure for mixing steel in ladle - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: procedure consists in mixing liquid steel by effecting it with impact pressure pulsations of blasting gas, when duration of pulses of maximal and minimal pressure of blasting gas is specifically set for each purger. Each purger operates under independent mode parallel-simultaneously with other facilities or independently from them. Implementation of the disclosed procedure facilitates total mixing of whole cross section of the ladle and whole volume of steel in the ladle with alloying additives and ferroalloys introduced into steel, also facilitates maximal withdrawal of non-metallic inclusions while maintaining uniformity of a slag layer.

EFFECT: upgraded quality of steel.

2 dwg, 2 tbl, 4 ex

Description

The proposed method relates to the field of metallurgy, in particular to the production of steel during processing in a ladle during the process of exhausting from a steel-smelting furnace and in out-of-furnace installations with steel purging with gas.

A known method of mixing steel in a ladle, carried out by purge gas through one or two purge tuyeres at a constant pressure of the supplied gas (Metallurg, 2004, No. 2). The disadvantages of this method are weak mixing, not covering the entire volume of the bucket due to the formation of a stable vertical flow of a mixture of gas and metal, and violation by the flow at the outlet of the continuity of the slag layer with exposure of the steel surface.

A known method of mixing steel in a ladle, including purging the steel from below with a gas or gas-powder mixture through the provided purge devices, at least one of which is offset from the vertical axis of the bucket towards its wall (RU 2197540 C2, published 2003.01.27). The movement relative to the steel of the purge devices in the horizontal plane is carried out by swinging rotation of the bucket relative to its vertical axis. However, mixing in this case does not cover most of the volume of the bucket, which reduces the efficiency of the method.

A known method of mixing steel in a ladle, including purging the steel with gas through at least two blowing tuyeres with a gas supply through each tuyere continuously with different intensities, which is changed according to a sinusoidal law (RU 2304172, published 2007.08.10). The method accelerates the process of mixing metal in a steel pouring ladle, which allows to reduce the processing time of the metal, to reduce the consumption given during the processing of metal materials.

The disadvantage of this method is that the sinusoidal law predetermines a smooth change in the purge gas supply intensity, which also smoothly changes the nature of the gas-metal mixture flows formed above the tuyeres with the formation of steady-state vertical flows, not ensuring full coverage of the bucket cross-section.

Closest to the proposed method according to the principle of variable purge gas supply is a method of mixing steel in a ladle with a purge of steel from below through gas through two purge devices, in which the purge is carried out alternately - first through one device, then through another located on the other side of the bucket (RU 2208054 C1, published 2003.07.10). Moreover, in the purge device, through which no purging is currently carried out, pressure is maintained to prevent metal from flowing into it.

The disadvantages of this method are as follows:

- steel mixing is not complete, since only at the moment of switching the purge gas supply from one device to another, stable vertical two-phase gas-metal flows are destroyed. Further, until the next switch, an expanding two-phase vertical flow is established above the devices, which does not cover the entire volume of metal in the ladle;

- modes of mixing water with gas purging, created in a cold ladle model with cold water and proposed by this method for purging and mixing molten steel in a ladle, cannot reflect the real processes occurring in a real ladle with real steel melted to + 1600 ° С. In real liquid steel, gas blown from below, at constant or periodically constant pressure of the purge gas, 5-8 seconds after the purge is turned on, steady vertical flows of gas-liquid mixture arise with practically no intensive lateral movements, poor coverage of the entire section of the bucket and insufficient mixing of steel ;

- the following drawback is a consequence of the previous one: due to the occurrence of steady-state vertical flows of a mixture of gas with steel with an insignificant cross-section, these flows when they exit onto the steel surface break the continuity of the specially induced slag layer in the form of so-called “spots” and create steel contact that is contrary to the technology with the atmosphere.

The basis of the invention is the technical problem, which consists in improving the quality of steel by ensuring uniformity of the composition of the melt by intensively mixing it in the entire volume of the ladle, as well as by reducing the sulfur content in the melt by removal of sulfur compounds by the purge gas bubbles.

To solve this problem in a method of mixing steel in a ladle, including continuously purging steel from below with gas at different intensities through at least two purging devices, according to the invention, purging gas is supplied to each purging device or to one of them when closed (s ) other device (s) in the mode of shock pressure pulsation, while the duration and intensity of the pulses of the maximum and minimum purge gas pressures are set individually for each device TWA, and each device works in independent mode or in parallel-simultaneously with other devices.

Through one device with another device closed, purge gas is supplied in the specified mode in emergency cases, for example in an emergency.

The process of blowing liquid steel from below with gas occurs according to the following laws of hydrodynamics of a gas-liquid system, when "... when a gas jet flows into a liquid, a more or less significant gas plume forms, which then breaks up into bubbles and creates its continuation in the form of a gas-liquid mixture stream." (Kutateladze S.S., Styrikovich M.A. / Hydrodynamics of gas-liquid systems. / Monograph. / M.: Energy. 1976. - Chapter 4-10.)

The difference between the method is that the purge gas is supplied to the molten steel in the mode of shock pulsation of pressure, not allowing the creation of a more or less significant gas torch (steady vertical flow), is crushed into bubbles at an early stage and covers the lowest layers of molten steel.

A feature of the proposed method is that gas is supplied to each purge device in the mode of shock pressure pulsation. Moreover, for each purge device, the maximum Pmax and the minimum Pmin pressure and the supply duration Pmax and Pmin are individually set. The intensity (flow rate, l / min) is always associated with the pressure drop across the purge device (or the pressure in front of the purge device), and since the pressure in the supply process is set to pulsating, the intensity also changes during the gas supply through one purge device. Since the pressures Pmax and Pmin for each purge device are set individually and with different durations, the intensity of gas supply through each purge device is different.

If we consider the gas supply in shock pressure pulsation mode (see the graph of figure 2), for example, for two purge devices, and compare with the gas purge mode according to a sinusoidal law, as in the prototype, then the differences of the proposed method from the known (prototype) are visible. In the proposed method for mixing steel in a ladle, a change in pressure is the main reason for changing the intensity of gas supply, and in the prototype method another principle for changing the intensity of gas purging is a change in gas flow according to a sinusoidal law. Table 1 gives the values of Pmax and Pmin for plotting the pressure supply of the two purge devices.

The invention is illustrated in figure 1, which shows a bucket with stirred steel and devices for supplying a purge gas.

The method is as follows.

In the process of releasing steel from the steelmaking furnace, the ladle 1 is filled with steel 2, on the surface of which a layer of liquid-moving highly basic slag 3 is induced to prevent contact of the steel with the atmosphere and absorption of impurities.

The pulsating supply device 4 (Fig. 1), powered by constant-pressure purge gas from the (workshop) network, in accordance with a given pulse duration of high and low pressure, creates a shock pulsation of the gas pressure at the outlet of one, two or more channels, through which the gas it is supplied to the purge devices 5 and then to the molten steel in the bucket 1. The pulse duration is selected in such a way that at a minimum and maximum pressure the steady-state vertical flow of a gas-liquid mixture does not have time to form. The gas flow from the purge device “breaks up” into a much denser medium (liquid steel) into discrete components (bubbles), expanding in the horizontal direction and covering the maximum volume of the bucket, as evidenced by the absence of “spots” of bare steel and uniform boiling of the entire induced highly mobile highly basic fluid slag 3.

Such a supply of purge gas in the mode of shock pressure pulsation is carried out during the release of steel from the furnace into the bucket.

Then the ladle with steel is transferred to the out-of-furnace steel processing unit (hereinafter referred to as “OVOS”), where the treatment is also performed with gas purging from below with gas in an automatic gas supply mode with shock pulsation of pressures.

Then the steel from the ladle is discharged into the intermediate ladle of the continuous steel casting installation, where it is also subjected to gas purging from below in the same mode of purging gas supply.

The method can be implemented by known devices. For example, as a device for supplying pressure in pulsation mode, gas flow distributors commonly used in industry having high speed can be used. When testing the method, the applicants used distributors with a switching time of 8 ms (0.008 sec), which made it possible to realize pressure supply in shock mode. Switching, the distributor connects the purge device either to the line with pressure Pmax, or to the line with pressure Pmin.

An industrial controller (in the case of an electrically controlled distributor) or a control device that implements the same functions and is assembled from elements of industrial pneumatic automatics operating on gas used in gas can be used as a control device for a distributor (a device that sends signals to switch the distributor at certain intervals) purge (in the case of a valve with pneumatic control, which was implemented by the applicants).

Conventional pressure reducing valves for gaseous media can be used to generate pressures Pmax and Pmin.

The following are examples of the method with the known and proposed modes of purging molten liquid steel from the bottom of the gas through a purge device located in the bottom of the bucket. In all the regimes, a layer of liquid-moving highly basic slag was induced on the surface of the steel, designed to prevent contact of liquid steel with the atmosphere and the absorption of impurities removed from the steel, including sulfur.

Example 1 (known method)

Smelted steel - Steel 20A, Steel D.

Purge through two devices from the bottom with gas continuously at first when steel is released from the furnace into the ladle, and then during the treatment at the air-blast furnace (ladle furnace). The purge was carried out with constant pressure gas from the workshop network without a pulsating feed device. Before the release, the sulfur content in the furnace averaged 0.031. Bucket filling time 10 ... 15 min.

During the purge, a break in the slag layer in the form of so-called “spots” with a diameter of about 300 mm and a bucket diameter of 3000 mm was visually observed. "Spots" are formed above the vertical vertical gas supply devices located in the bucket bottom, which indicates the occurrence of steady vertical flows of a mixture of gas and steel with insignificant coverage of the bucket cross section and, accordingly, incomplete mixing of the volume of steel in the bucket. After filling the bucket and completing the purge, the sulfur content averaged 0.021. Subsequent treatment for air treatment with a similar purge gave an average sulfur content of 0.014. The mode provides a decrease in sulfur by 2.2 times.

Example 2 (known method)

Smelted steel - Steel 20A.

Discharge from the furnace to the bucket, then treatment for air pollution control.

Steel was purged from below through gas through two purge devices located on different sides of the bucket, in turn - first through one of the devices, then through the other. At the same time, in the purge device through which no purge was currently carried out, pressure was maintained to prevent metal from flowing into it. The period of changing the supply of full pressure in one or another device was changed from 10 to 50 seconds. In any case, the shift (reverse) period after 5 ... 8 sec. On the surface of the slag layer in the bucket there was a break of the slag ("spot"), which indicates the formation of steady vertical flows in the bucket. Sulfur content: in the furnace before the release, on average, 0.030, in the bucket after the treatment for air pollution control, on average 0.017. 2.3 times lower sulfur content.

Example 3 (the proposed method)

Smelted steel - Steel 20A, Steel D.

Purge — through two devices from the bottom, gas continuously with different purge gas supply rates in the shock pulsation pressure mode, while the maximum and minimum duration of the purge gas pressure pulses were set individually for each purge device, and each device worked independently in parallel with the other and regardless of him.

The purge mode was initially performed when steel was released from the open-hearth furnace. Then the same bucket was transferred to the air defense system. The time of release of steel from the furnace 10 ... 15 minutes The processing time for UVOS technology is about 45 minutes.

During the purging process, a rupture of the slag layer was not observed; the slag was subjected to vibrational vibration on the entire surface.

In total, 8 heats were produced in the experiment. The analysis results showed the following sulfur content:

table 2

Melting In the oven After graduation Ablation Decline one 0,026 0.018 0.005 5.2 times 2 0,029 0.019 0.010 2.9 times 3 0,033 0.013 0.008 4.1 times four 0,039 0.012 0.008 4.9 times 5 0,041 0.017 0.008 5.1 times 6 0,032 0,022 0.004 8 times 7 0,027 0.017 0.003 9 times 8 0,029 0,021 0.005 5.8 times

Example 4 (the proposed method with a single gas supply device)

Pulsating steel gas purging was carried out through one device in the mode of shock pulsation of the purge gas pressure in the process of steel discharge from the open-hearth furnace.

During the purging process, a breakdown of the slag layer was not observed; there was a general oscillation of the surface of the slag layer, which implies the creation of a gas-steel mixture flow with a significant coverage of the ladle cross section and sufficient mixing of the volume of steel in the ladle. This mode is usually not used in the technological process, however, it can be used in an emergency when one gas supply device is working.

The results of examples of modes of mixing steel in a ladle showed the greatest efficiency of the proposed method with a gas supply in the mode of shock pressure pulsation according to example 3.

Using the proposed method allows to cover with mixing the entire cross section of the ladle and the entire volume of steel in the ladle with alloying additives and ferroalloys introduced into the steel, as well as to ensure maximum removal of non-metallic inclusions without violating the continuity of the slag layer.

Using the proposed method of mixing in the production of steel during processing in the ladle during the process of exhausting from the steelmaking furnace and in out-of-furnace plants with steel gas purging provides the following technical results:

- the formation of steady-state flows of purge gas in a mixture with liquid steel is excluded, thereby violating the continuity of the slag layer, exposure of the steel and its contact with the atmosphere;

- the slag layer is subjected to vibrational vibrations on the entire surface in the bucket, which allows you to enter the necessary materials not in the "spot", as forced to perform on out-of-furnace steel processing plants (ladle furnace), but in any place on the surface of the slag, and the given materials are easily and quickly penetrate through a layer of oscillating slag into steel, where they mix;

- the bucket cross-section is maximally covered by purge gas bubbles, compounds of oxides, sulfides, silicates, sulfur, and other nonmetallic inclusions are removed by gas bubbles from steel and absorbed by porous liquid-moving highly basic slag over its entire area on the surface of the steel in the bucket;

- intensive mixing of the entire volume of steel in the ladle with alloying additives and ferroalloys introduced into the steel is carried out;

- the uniformity of the composition of the molten steel is stabilized in the entire volume of the ladle, which subsequently positively affects the quality of crystallization of liquid steel in the process of continuous casting.

As a result, the method provides a significant increase in the quality of steel, which is determined by the intensity of desulfurization, since a decrease in sulfur content is one of the main indicators of the quality of steel.

Table 1 sheet 1 P max P min T max T min T step fifteen 3 0.5 2 0.008 Time 0 0.008 0.016 0.024 0,032 0.04 0,048 0.056 0,064 0,072 0.08 0,088 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 0,096 0.104 0,112 0.12 0.128 0.136 0.144 0.152 0.16 0.168 0.176 0.184 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 0.192 0.2 0.208 0.216 0.224 0.232 0.24 0.248 0.256 0.264 0.272 0.28 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 0.288 0.296 0,304 0.312 0.32 0.328 0.336 0.344 0.352 0.36 0.368 0.376 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 0.384 0.392 0.4 0.408 0.416 0.424 0.432 0.44 0.448 0.456 0.464 0.472 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 0.48 0.488 0.496 0.504 0.512 0.52 0.528 0.536 0.544 0.552 0.56 0.568 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 0.576 0.584 0.592 0.6 0.608 0.616 0.624 0.632 0.64 0.648 0.656 0.664 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 0.672 0.68 0.688 0.696 0.704 0.712 0.72 0.728 0.736 0.744 0.752 0.76 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 0.768 0.776 0.784 0.792 0.8 0.808 0.816 0.824 0.832 0.84 0.848 0.856

Table 1 sheet 2 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 0.864 0.872 0.88 0.888 0.896 0.904 0.912 0.92 0.928 0.936 0.944 0.952 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 0.96 0.968 0.976 0.984 0,992 one 1.008 1.016 1,024 1,032 1,04 1,048 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 1,056 1,064 1,072 1,08 1,088 1,096 1,104 1,112 1.12 1,128 1,136 1,144 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 1,152 1.16 1,168 1,176 1,184 1,192 1,2 1,208 1,216 1,224 1,232 1.24 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 1,248 1,256 1,264 1,272 1.28 1,288 1,296 1,304 1,312 1.32 1,328 1,336 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 1,344 1,352 1.36 1,368 1,376 1,384 1,392 1.4 1,408 1,416 1,424 1,432 Pressure 1 3 3 3 3 3 3 3 3 3 3 3 3 Pressure 2 four four four four four four four four four four four four Time 1.44 1,448 1,456 1,464 1,472 1.48 1,488 1,496 1,504 1,512 1,52 1,528 Pressure 1 3 3 3 3 3 3 3 3 fifteen fifteen fifteen fifteen Pressure 2 four four four four four four four four four four four four Time 1,536 1,544 1,552 1,56 1,568 1,576 1,584 1,592 1,6 1,608 1,616 1,624 Pressure 1 fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen Pressure 2 four four four four four four four four four four four four Time 1,632 1,64 1,648 1,656 1,664 1,672 1.68 1,688 1,696 1,704 1,712 1.72

Table 1, sheet 3 Pressure 1 fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen Pressure 2 four four four four four four four four four four four four Time 1,728 1,736 1,744 1,752 1.76 1,768 1,776 1,784 1,792 1.8 1,808 1,816 Pressure 1 fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen Pressure 2 four four four four four four four four four four 13 13 Time 1,824 1,832 1.84 1,848 1,856 1,864 1,872 1.88 1,888 1,896 1,904 1,912 Pressure 1 fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen Pressure 2 13 13 13 13 13 13 13 13 13 13 13 13 Time 1.92 1,928 1,936 1,944 1,952 1.96 1,968 1,976 1,984 1,992 2 2,008 Pressure 1 fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen 3 Pressure 2 13 13 13 13 13 13 13 13 13 13 13 13 Time 2,016 2,024 Pressure 1 3 3 Pressure 2 13 13

Claims (1)

A method of mixing steel in a ladle, including purging the steel from below with gas continuously at different intensities through at least two purge devices provided, characterized in that the purge gas is supplied to each purge device or to one of them when other purge devices are closed in shock mode pressure pulsations, while the duration and intensity of the pulses of the maximum and minimum purge gas pressures are set individually for each device, and each device works It runs in parallel-simultaneously with other devices or independently in independent mode.

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