KR100826907B1 - Refining method of molten steel - Google Patents

Abstract

A refining method of molten steel is provided to improve productivity of a converter by preventing non-ignition generated in the early stage of refining, reduce the maintenance cost by preventing flattening of a lace nozzle, and reduce the management cost of the facilities by preventing facility degradation due to small explosion within facilities. A refining method of molten steel comprises: a slag skimming step(S20) of setting up a converter tilting angle for slag skimming according to life of a furnace body and operational circumstances of a converter to determine a residual slag amount; a converter inner wall coating step(S30) of determining the amount of a coating agent charged into the converter and the flow rate of nitrogen ejected into the converter according to a condition of the remained slag in the slag skimming step; and a conventional blowing step(S60) of adjusting the height of a lance and the supply pressure of oxygen correspondingly to thickness of a residual slag layer estimated according to the remained slag amount. The refining method further comprises a tapping completing step(S10) prior to the slag skimming step. The refining method further comprises an additional slag skimming step(S40) and an iron scrap/hot metal charging step(S50) between the converter inner wall coating step and the blowing step. The refining method further comprises a tapping step(S70) after the blowing step.

Description

Refining method of molten steel}

1 is a flowchart showing a molten steel refining method in a general converter,

2 is a flow chart showing a molten steel refining method in the converter according to the present invention,

3 is a graph showing the upsetting pattern of the blowing step according to the present invention,

4 is a drawing comparing the initial blow point of the comparative example and the embodiment,

5 is a graph comparing the number of occurrences of small explosions in Comparative Examples and Examples,

6 is a graph comparing the number of visible dusts generated in Comparative Examples and Examples.

The present invention relates to a molten steel refining method, and more particularly, in order to determine the amount of slag remaining in the converter during refining, to set the tilt angle when the slag is disposed in accordance with the life of the body and operating conditions, according to the state of the remaining slag The present invention relates to a molten steel refining method that can correct the amount of coating agent and nitrogen flow injected during slag coating, improve the initial refining pattern and prevent unignition, and improve the coating efficacy of the converter inner wall.

In general, the molten steel refining method performed in the converter, when the tapping of the molten steel produced in the pre-operation process is completed as shown in FIG. 1 (during tapping step; S1), a predetermined amount of slag is firstly disposed (slag first) Exclusion step: S2), after establishing the converter, injecting a coating agent such as dolomite and light dolomite, and then spraying high pressure nitrogen on the upper part using a lance to apply a certain amount of coating agent to the confectionery as a whole, and then using the remaining residual slag While tilting back and forth to coat the road part and the tapping side (electric converter inner wall coating step; S3).

After this operation (S3) is completed, the slag is secondarily discharged to leave the proper amount of slag necessary for refining (slag secondary discharging step; S4). Injecting the protective lime, and charging the scrap iron and molten iron (scrap iron / molten iron charging step; S5) and starts blowing by spraying oxygen using a lance (blowing step; S6). During the refining operation, the coolant and the preparation are added by heat balance, and the working time is generally about 17 minutes.

Then, when the drilling process (S6) is completed, the tapping, which is the step of transferring the molten steel in the ladle (tapping step; S7), at this time to adjust the components and temperature according to the steel type. When all the molten steel is discharged and slag is discharged, finishing the tapping is a series of tasks to be completed, and the above-mentioned operations are repeated continuously.

Ignition occurs in the blowing process (S6), "ignition" refers to the oxygen supplied from the lance penetrates the molten iron through the residual slag layer of a certain thickness.

This ignition does not occur normally, the phenomenon that the supply of oxygen after the start of the blow start, but the oxidation reaction does not occur in the molten iron for more than a certain time is called "unignition".

The non-ignition usually occurs because oxygen injected from the lance does not penetrate the residual slag layer. For this reason, a technique for maintaining a constant amount of slag remaining in the converter is important, but it is not limited to the life of the body, the operation situation, and the state of the residual slag. As a result, the degree of slag exclusion was different and it was very difficult to maintain a constant amount of residual slag after exclusion.

If the unignition persists as described above, oxygen introduced into the exhaust gas duct reacts with the existing carbon monoxide remaining in the duct, causing a small explosion in the duct or the dust collector.

As dust generated by the small explosion was discharged, visible dust, which is the main cause of air pollution, was generated, and facility deterioration occurred due to internal explosion, thereby increasing facility management costs. In addition, when the non-ignition occurs, the oxygen injected from the lance is reflected by the slag in the furnace to cause wear of the nozzle portion of the lance to generate a lance puncture, resulting in lower productivity and increased maintenance costs.

The present invention has been made to solve the above problems, to prevent the non-ignition occurs during the initial refining to improve the converter productivity by the blow stop, to prevent the puncture of the lance nozzle, to reduce the maintenance cost, small inside the facility The aim is to provide a method of refining molten steel that can reduce facility management costs by preventing deterioration of equipment.

In the molten steel refining method according to the present invention for achieving the above object, in the molten steel refining method, the slag excretion step of determining the residual slag amount by setting the converter tilt angle for slag exclusion according to the furnace life and operation conditions; A converter inner wall coating step of determining an amount of coating agent and a nitrogen flow rate injected according to the state of slag remaining in the slag discharging step; And a blowing step of adjusting the lance height and the oxygen supply pressure according to the thickness of the residual slag layer estimated according to the amount of the remaining slag.

In the slag exclusion step, when the number of furnace bodies is used 500 times or less, the tilt angle of the converter is maintained at 99 ± 0.5 degrees. When the number of furnace bodies is used more than 500 times, the tilt angle is gradually increased as the number of furnace bodies is increased. It may be desirable to increase the setting.

In addition, the tilt angle of the converter in the slag excretion step is any one of the operating conditions of when the furnace is now attached in large quantities, when the tapping time exceeds 7 minutes, the end point oxygen temperature of more than 600 degrees, when re-refining, deodorizing, slag viscosity If it is, it is preferable to correct the set tilt angle by +1 to +3 degrees, and to correct the set tilt angle by -1 degrees when the departure time is 4 minutes or less.

And, the coating agent to be charged in the converter in the converter inner wall coating step is the dolomite and light dolomite, the loading amount of the fresh dolomite gradually increases between 500 ~ 1500kg as the dissolved oxygen content of the molten steel, The loading amount is characterized by gradually increasing between 1500 ~ 2500kg as the dissolved oxygen of the residual slag increases.

In addition, the nitrogen flow injected in the converter inner wall coating step is characterized by gradually increasing between 800 ~ 1000N ㎥ per minute as the amount of dissolved oxygen in the molten steel increases.

And, the blowing step is to form a odor pattern to adjust the lance height and oxygen supply pressure over time, the height of the lance and oxygen supply until the initial 3% time point of the process of the honche pattern up to the initial 30% By lowering the pressure, the flash point size up to the initial 3% time point is formed to be smaller than the initial 30% time point.

Hereinafter, the preferred embodiment of the molten steel refining method according to the present invention.

Figure 2 is a flow chart showing a molten steel refining method in the converter according to the present invention, the molten steel refining method according to the present invention as shown in Figure 2 is completed tapping step to finish the molten steel blown in the previous operation process (S10); Slag discharging step (S20) for excluding the slag remaining after the tapping; A converter inner wall coating step (S30) of charging the converter with a coating agent, spraying nitrogen, and tilting the converter to coat (repair) the inner wall of the converter using the coating agent, nitrogen, and residual slag; Scrap metal and molten iron charging step (S50) to put the protective lime for the protection of the old wear at the time of charging the steel, and to load the scrap iron and molten iron; Blowing step (S60) for performing the blowing by injecting oxygen using a lance; Completion of the blow is made including a tapping step (S70) for discharging the molten steel ladle.

At this time, after the converter inner wall coating step (S30) may further include a slag additional excretion step (S40) for leaving the slag of the appropriate amount required for refining.

1. Lecture completed S10 )

The molten steel produced during the pre-operation process is pulled out, and the molten steel is completed. The remaining slag amount in the converter is usually 25 to 30 tons at the completion of the molten steel.

2. Slag  Exclusion stage ( S20 )

When the tapping is completed, the slag in the converter is discharged to a certain amount. At this time, when the discharge is completed, the converter inner wall coating step (S30) and the blowing step (S60), which are described below, are preferably performed by maintaining the amount of the remaining slag at about 15 tons.

As described above, in order to maintain the amount of residual slag after completion of discharge in a variety of environments, the residual slag amount is kept constant by setting and excluding the tilt angle of the converter for slag exclusion according to the life of the furnace and the operation situation.

In the slag exclusion step (S20), the tilt angle of the converter is maintained at 99 ± 0.5 degrees when the number of use of the furnace body is 500 times or less, and when the number of use of the furnace body exceeds 500 times, the tilt angle is gradually increased as the number of use of the furnace body is increased. It would be desirable to set it up.

The reason why the tilt angle is increased and set as the number of use of the furnace body increases is that the aging method is accumulated as the number of use of the body is increased, and the amount of slag remaining varies according to the aging method. To reduce the amount of slag remaining.

For this reason, if the number of use of the furnace body exceeds 500 times, it would be desirable to set the tilt angle as shown in Table 1 below, and the following conditions are the optimum conditions obtained through several experiments.

division Number of furnace bodies used (times) 500 or less 501-1000 1001-2000 2001-3000 3001-4000 4001-6000 6001 or more Tilt angle (degrees) 99 ± 0.5 100 ± 0.5 101 ± 0.5 102 ± 0.5 103 ± 0.5 104 ± 0.5 105 ± 0.5

Further, the converter tilt angle is more preferable to perform slag exclusion by correcting the tilt angle according to the refinement operation situation based on the tilt angle shown in Table 1 above.

The tilt angle correction value of the converter according to the refining operation situation is shown in Table 2 below.

Item At the time of a lot of attachment now Time End point oxygen temperature Retraining Deemed It's a slag viscosity. 4 minutes or less More than 7 minutes 600-700 700 or more Correction angle +2 degrees -1 degree +1 degree +1 degree +2 degrees +2 degrees +2 degrees +3 degrees

The conditions of Table 2 are also the conditions derived to satisfy the optimum conditions to make the residual slag amount constant through several experiments.

If the reason for increasing or decreasing the tilting angle as shown in Table 2 described below.

When there is a large amount of current in the furnace, even if the slag is discharged at the tilt angle set by the furnace, the worker is not discharged as much as the target slag amount, and as the amount of residual slag increases, the tilt angle is increased to reduce the deviation. For sake.

The correction of tilt angle according to the tapping time is not only the molten steel tapping into the ladle during tapping, but also the slag flows out. The longer tapping time is, the less tapping flow, the less slag outflow, and the shorter tapping time, the more tapping taps. As the slag outflow increases, the long tap time increases the tilt angle, and the short tap time decreases the hardness angle to reduce the deviation.

The correction of the tilt angle according to the end point oxygen temperature increases the T.Fe in the slag as the end point oxygen temperature increases, so the volume of the slag increases. As the end point oxygen temperature increases, the hardness angle increases so that the amount of residual slag remains constant. This is to maintain.

In addition, since the volume of slag increases because the amount of T.Fe in the slag increases even during re-treatment, the tilting angle is increased to maintain the amount of the remaining slag constant.

In addition, during the deodorization, iron and oxygen in the present reaction react to increase T.Fe and increase the volume of slag, so that the tilt angle is increased so that the amount of the remaining slag is kept constant.

Since the slag viscosity again FeO is present in the slag because the presence of a large amount of slag, in order to improve the coating property in the converter inner wall coating step (S30) to increase the amount of coating agent by the amount.

3. Coating of inner wall of converter S30 )

Excluding the residual slag in accordance with the converter tilt angle obtained in Table 1 and Table 2, and then the coating agent is charged, the nitrogen is injected, the converter is tilted to apply nitrogen spray coating and residual slag coating.

In this case, the amount of coating agent charged into the converter and the injected nitrogen flow rate are preferably determined according to the state of the remaining slag.

When the coating agent is used together with the dolomite (dolomite) and light dolomite (dolomite), in the slag discharging step (S20) when the amount of residual slag is maintained to about 15 tons, the standard dosing of the raw dolomite is 1 ton, light dolomite The standard dosage of is preferably 2 tons.

However, the input amount of the raw dolomite and light dolomite is preferably corrected based on the reference dose according to the state of the residual slag (determined by the dissolved oxygen amount (ppm) of the molten steel), and the correction amount of the coating agent is shown in the following table. 3 is shown.

Item Coating Slag state (estimated ppm) Saint Dolomite Light dolomite Dry (less than 450) Standard-500 kg Standard-500 kg Low dryness (450 ~ 500) Standard-500 kg Standard input amount Medium (500-600) Standard input amount Standard input amount Drug property (600 ~ 700) Standard + 500 kg Standard input amount Physical property (over 700) Standard + 500 kg Standard + 500 kg Retraining Standard + 500 kg Standard + 500 kg Deemed Standard + 500 kg Standard + 500 kg

In addition, in the case of nitrogen injected into the converter, as in the coating agent, the reference flow rate of nitrogen injected into the converter is preferably 800 Nm3 / min when the amount of residual slag is maintained at about 15 tons in the slag discharging step (S20).

However, it is preferable that the injection flow rate of nitrogen is also corrected based on the reference flow rate according to the state of the remaining slag as in the coating agent, and the injection flow rate correction value of nitrogen is shown in Table 4 below.

Item Nitrogen injection flow rate Dry (less than 450) Standard flow Low dryness (450 ~ 500) Standard flow Medium (500-600) Standard flow Drug property (600 ~ 700) Standard flow rate + 100N㎥ Physical property (over 700) Standard flow rate + 200 N㎥ Retraining Standard flow rate + 200 N㎥ Deemed Standard flow rate + 200 N㎥

The correction values of the coating agent and nitrogen shown in Tables 3 and 4 are also optimum conditions obtained through several experiments so that nitrogen spray coating and residual slag coating can be carried out correctly.

As shown in Table 3 and Table 4, the amount of coating and the injection flow rate of nitrogen increases as the state of the slag goes from dry to physical properties, which is because the state of slag changes from dry to physical properties. ppm) increases, and the amount of T.Fe in the slag is determined according to the amount of dissolved oxygen. As the amount of dissolved oxygen increases, the amount of T.Fe increases.

And, the slag fluidity varies according to the amount of T.Fe. If the amount of T.Fe is small, the slag fluidity decreases, and thus the amount of slag remaining in the furnace increases, so that unsettling occurs during the initial refining work. The amount of the coating agent is corrected as shown in Table 3, and the amount of slag remaining is fixed by correcting the injection flow rate of nitrogen as shown in Table 4 to prevent unignition.

4. Slag  Additional exclusion stages ( S40 )

After the nitrogen spray coating and the residual slag coating may further include a slag additional excretion step (S40) for further exclusion of slag in order to properly adjust the amount of slag remaining in the converter.

By performing the slag additional exclusion as described above, the amount of residual slag is kept constant to prevent unignition during refining, and it is preferable to keep the amount of residual slag remaining in the converter about 13 to 15 tons.

5. Scrap metal / molten iron S50 )

When lime is charged, the protection lime is added to protect the old abdomen. Since the protection lime causes a problem of increasing the amount of residual slag, it is preferable to constantly input the amount of the protection lime.

Charge the lime and the molten iron after adding protective lime. Then, the residual slag layer is formed on the molten iron.

6. Drilling stage ( S60 )

When charging of scrap metal and molten iron is completed, oxygen is blown in using a lance and a blow start is started.

At this time, the height of the lance (gap from the hot water surface to the bottom of the lance) and the amount of oxygen blown are important factors for the ignition to occur preferably during the blowing process. And, the height of the lance and the delivery flow rate should be adjusted to each other organically over time, for this reason, the upsetting pattern is provided.

Figure 3 is a graph showing the pattern of the height and the transmission flow rate of the lance during the blowing step (S60) according to the present invention, in the present invention as shown in Figure 3 the height of the lance to the initial 3% during the process to 220cm And a pattern for maintaining the oxygen supply pressure at 550 Nm 3 / min.

At the time when the process passes 3%, the height of the lance is raised to 240cm, and the flow rate is increased to 850 Nm3 / min to maintain the process up to 30% of the time. The firing point (the contact surface between molten iron and oxygen jet) is made smaller (to close the hot water surface and the lance), and the oxygen injected is concentrated, so that the residual slag layer can be easily drilled to facilitate the contact with the molten iron. .

If the height of the lance is less than 220cm, the nozzle portion of the lance may be damaged by the oxygen sprayed initially. If the lance is more than 220cm, the flash point is relatively large, so that the residual slag layer cannot be easily penetrated, and thus the frequency of unignition occurs. Increases.

This concentration of oxygen is injected to penetrate the residual slag layer, and after 3% of the process, the lance is increased to 240cm while raising the flow rate to 850N㎥ / min together with the height of the lance to increase the ignition to make it desirable. .

After 30% of progression, the upsetting pattern is the optimum condition obtained through several experiments to make the ignition desirable.

7. Lecture stage S70 )

The ignition is preferably made in the blowing step (S60) so that when the blow is completed, the molten steel produced into the ladle is pulled out.

Hereinafter, the preferred embodiment of the present invention will be described in comparison with the comparative example.

EXAMPLE

While proceeding a series of refining process according to the above-described preferred embodiment of the present invention, the tilt angle, coating amount and nitrogen injection flow rate were determined according to the values determined by Tables 1 to 4, and the blowing is shown in FIG. It proceeded according to the smell pattern.

The shape of the flash point at the beginning of the blow (3% progress point), the number of small explosions and the frequency of visible dust generation were observed in the duct or the dust collector.

[Comparative Example]

While proceeding a series of refining process according to the above-described preferred embodiment of the present invention, the tilt angle was tilted to 99 degrees on average, and the coating agent was charged with 1000kg of fresh dolomite, 2000kg of light dolomite, and the nitrogen injection flow rate was 800Nm3 / min. While maintaining the pressure, each correction value was determined by the operator's experience value according to the operation situation, and the blow was maintained at the height of the lance 220cm until the initial 3% of the blow out pattern shown in Figure 3, the oxygen supply pressure It did not include the pattern to maintain the 550Nm 3 / min, the height of the lance was maintained 240cm until the initial 30% of the blowing, and the uptake pattern was maintained to maintain the delivery flow rate at 850Nm 3 / min.

The shape of the flash point at the beginning of the blow (3% progress point), the number of small explosions and the frequency of visible dust generation were observed in the duct or the dust collector.

The results of the above [Examples] and [Comparative Examples] are as follows.

4 is a drawing comparing the initial firing point of the comparative example and the embodiment, Figure 5 is a graph comparing the number of small explosions of the comparative example and the embodiment, Figure 6 compares the number of visible dust generation of the comparative example and the example It is a graph.

First, as shown in FIG. 4, the firing area of the embodiment is narrower than that of the comparative example, as shown in FIG. 4, so that the injected oxygen is concentrated in a narrow area and the residual slag layer is easily drilled.

And, as shown in FIG. 5 as a result of confirming the number of small explosions generated in the duct or dust collector by comparing the comparative example and the example, the annual comparative example generated 185 times, while the example is generated 20 times Significantly decreased more than 160 times a year.

In addition, as shown in FIG. 6, when the number of visible dusts was confirmed by comparing the comparative example and the example, the annual comparative example was generated 36 times, whereas the example was generated only three times, which is significantly reduced more than 30 times a year. It was.

As described above, the present invention sets the tilt angle according to the service life and operating conditions of the converter in the residual slag discharging step, and sets the coating agent and the nitrogen flow rate according to the remaining slag state of the converter in the converter inner wall coating step, and at the same time, blows it in the drilling step. By improving the initial intake pattern, it is possible to prevent unignition, thereby improving converter productivity and reducing the maintenance cost of the lance.

In addition, there is an effect that can prevent a small explosion in the facility according to the prevention of unignition, and to improve the efficacy of the converter inner wall coating to reduce the equipment management cost.

Claims (12)

In the molten steel refining method, The tilt angle of the converter is set to 99 ± 0.5 degrees, and when the number of use of the furnace body exceeds 500 times, the tilt angle is gradually incremented by 1 degree after 500, 1000, 2000, 3000, 4000, and 6000 times. The slag discharging step of increasing and setting the amount of residual slag; The amount of the coating agent and the injected nitrogen flow rate are determined according to the state of the slag remaining in the slag discharging step, wherein the coating agent is chlorinated dolomite and light dolomite, and when the dissolved oxygen content of molten steel is less than 500 ppm 500kg, 1000kg when the dissolved oxygen content of the molten steel is 500 ~ 600ppm, 1500kg when the dissolved oxygen content of the molten steel exceeds 600ppm, the loading amount of the light dolomite is 1500Kg, dissolved oxygen amount of the molten steel is less than 450ppm 2000kg at 450 ~ 700ppm, 2500kg when dissolved oxygen exceeds 700ppm, and injected nitrogen flow rate is 800N㎥ per minute when dissolved oxygen is less than 600ppm, and dissolved oxygen is 600 ~ 700ppm 900Nm 3 / min, when the dissolved oxygen content of the molten steel exceeds 700ppm and the inner wall coating step of spraying at 1000Nm / min; Forming a refreshing pattern to adjust the lance height and oxygen supply pressure as time passes, while maintaining the height of the lance at 220cm until the initial 3% of the process of the refreshing pattern, the oxygen supply pressure to 550N㎥ / min A molten steel refining method comprising a blowing step comprising a holding pattern to maintain. delete delete The method of claim 1, The tilt angle of the converter in the slag excavation step corresponds to any one of the operating conditions of when the furnace is now attached in large quantities, when the tapping time exceeds 7 minutes, when the end point oxygen temperature is higher than 600 degrees, when re-refining, deodorizing, and slag viscosity occur When the molten steel refining method characterized in that for correcting +1 ~ +3 degrees. The method of claim 1, And the tilt angle of the converter in the slag exclusion step corrects the set tilt angle by -1 degree when the tapping time is 4 minutes or less. delete The method of claim 1, The molten steel refining method characterized in that the loading amount of the raw dolomite charges 1500 kg when the operation condition is in the re-scavenging or de-airing situation. The method of claim 1, The molten steel refining method, characterized in that the loading amount of the light dolomite is added to 2500kg when the operation conditions are re-refining or de-airing. delete The method of claim 1, The molten steel refining method, characterized in that the nitrogen flow rate is 1000N ㎥ per minute when the operating conditions are re-blowing or de-coiling. The method of claim 1, Molten steel refining method characterized in that to maintain the height of the lance to 240cm, the oxygen supply pressure to 850Nm3 / min from the initial 3% time point to the initial 30% time point during the progress of the intake pattern in the blowing step. delete

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