KR101485530B1 - Method of refinig molten steel - Google Patents

Abstract

According to an embodiment of the present invention, there is provided a method of refining a molten iron, comprising the steps of completing the ladle furnace produced in the previous refining step, tilting the converter to exclude a part of the slag generated in the previous process, Charging a charcoal to be used in the present process, charging the charcoal, and discharging the slag generated by the cigarette after the cigarette is introduced into the slag remaining in the converter The phosphorus in the charcoal can be easily removed. That is, after partially disposing the slag accommodated in the converter where the previous process is completed, the lime CP is added to another slag remaining in the converter to increase the amount of Fe 2 O 3 produced in the slag, By vaporizing phosphorus by phosphorus, phosphorus can be partially removed prior to the first blowing, thereby increasing the talline ratio.
Accordingly, it is possible to reduce the amount of CaO injected into the molten iron in the primary refining step, thereby reducing the cost of CaO consumed in refining the molten iron.
Further, by controlling the process environment, the entire process can be stably performed, and the problems caused by the component control mistake can be solved in the past, and the quality of the finally produced product can be improved.

Description

[0001] METHOD OF REFINING MOLTEN STEEL [0002]

The present invention relates to a method for scouring a molten iron, and more particularly, to a method for scouring a molten iron which can easily remove molten iron.

In general, the phosphorus (P) component contained in molten steel is segregated in the cast steel during continuous casting, causing quality defects, and particularly cracking of the material under extreme environments, adversely affecting the product. As a result, under extreme conditions, materials such as pressure vessels and pipes are mainly used for ultra-low-strength steels which are resistant to stress corrosion cracking caused by hydrogen organic cracking or sulfides.

On the other hand, the steelmaking process proceeds in the order of the iron pre-treatment process, the converter refining process, the secondary refining process, and the continuous casting process.

At this time, the converter refining process charges hot metal and scrap into the converter and blows oxygen (O ₂ ) gas of high purity through the lance, so that the carbon and impurities in the charcoal are converted into the oxide of CO gas or slag The molten steel from which impurities have been removed through this process is called molten steel.

The slag layer formed in the reaction of removing the oxide form of the slag actively reacts with the molten iron by stirring action by the impact energy of the off-gas (N ₂ , Ar) and pure oxygen to stably remove the impurities in the molten iron, Lt; / RTI > plays a very important role in removing and stabilizing the component (P).

Conventionally, for the process of removing the phosphorus (P) component, the phosphorus phosphorus is removed while the double slag operation and the talline operation are performed, and the basicity of the slag is an important factor in reacting with phosphorus (P).

However, due to the characteristics of the steelmaking operation, molten steel is produced using the same equipment. Therefore, even if all of the slag in the previous operation is discharged, the slag remaining in the converter is generated, There is a problem that a variation in the curing process is caused to cause a component control mistake.

Also, in the process of double slag operation and talline operation as in the prior art, nitrogen (N) is neglected in the production of low-grade low-carbon steel, which is a damper. At this time, in order to suppress and prevent the generation of nitrogen, it is required to input a large amount of CaO into the charcoal line, which causes a failure of goods due to the input of CaO and a cost increase in the CaO source.

KR 2000-0020060 A1

The present invention provides a molten iron refining method capable of easily removing iron phosphorus through controlling the basicity of slag.

The present invention provides a charcoal refining method capable of increasing the content of T.Fe (Total Fe) in a charcoal line before charcoal.

The present invention provides a charcoal refining method capable of reducing the amount of CaO (burnt lime) to be charged at the time of refilling of charcoal.

The present invention provides a charcoal refining method capable of improving the quality of a product to be produced.

According to an embodiment of the present invention, there is provided a method of refining a molten iron, comprising the steps of completing the ladle furnace produced in the previous refining step, tilting the converter to exclude a part of the slag generated in the previous process, Charging a charcoal to be used in the present process, charging the charcoal, and discharging the slag generated by the cigarette after the cigarette is introduced into the slag remaining in the converter .

The additive may include a lime CP having a CaO content of 50% or more.

The amount of slag remaining in the converter in the step of mixing may remain within 50% of the slag generated in the previous step.

The basicity of the slags in the converter can be adjusted to 4.5 or more to 5.5 or less.

The additive may be charged in an amount of 10 to 15% of the amount of slag remaining in the converter.

The step of blowing the charcoal includes a primary winding process and a secondary winding process, and the primary winding and the secondary winding can be performed with a time lag.

Before the step of charging the charcoal, it is possible to perform a step of injecting dolomite into the converter and blowing an inert gas to coat the inner wall of the converter.

According to the embodiment of the present invention, it is possible to easily remove the phosphorus (P) in the charcoal accommodated in the converter later by controlling the basicity of the slag by introducing the lime CP into a part of the slag generated in the previous step have. That is, after the slag accommodated in the converter where the previous process is completed is partially discharged, the basicity of the slag is controlled by introducing the lime CP into another slag remaining in the converter.

In this way, when the lime CP is introduced into the slag, the amount of Fe ₂ O ₃ is increased because the concentration of Fe in the slag is increased, and the reaction of phosphorus (P) and Fe ₂ O ₃ is increased to increase the talline ratio have.

Further, since the basicity of the slag is controlled in the curing process after the charcoal is charged in advance and a portion of the CaO (burnt lime) to be added to increase the amount of T.Fe can be replaced with the lime CP, The cost can be reduced.

Further, by controlling the process environment by controlling the slag basicity before the blowing, the whole process can be stably performed, and the problem caused by the component control mistake can be solved in the past, and the quality of the finally produced product can be improved.

1 is a diagram showing a typical converter and lance.
2 is a flowchart illustrating a method of scouring a charcoal according to an embodiment of the present invention.
Fig. 3 is a diagram showing the refining method of Fig. 2 in order.
Fig. 4 is a graph showing the behavior of [P] in the molten iron until the completion of the first refining according to the input of the lime CP.
5 is a graph showing the relation between the comparative example and the embodiment according to the slag ion ratio of the residual slag.
FIG. 6 is a graph showing the talline ratio of the molten iron and the firing rate of the lime CP at the time of feeding after the lime CP is charged according to the primary winding time.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be apparent to those skilled in the art that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know. Wherein like reference numerals refer to like elements throughout.

FIG. 1 is a flowchart showing a method of scouring a charcoal according to an embodiment of the present invention. Fig. 2 is a diagram showing the refining method of Fig. 2 in order. 3 is a view showing a comparison between a conventional scouring method and a scouring method according to the present invention.

The converter 100 and the lance 200 used in the present invention are generally used in a steelmaking process and will be briefly described.

Referring to FIG. 2, the converter 100 includes a vessel having an inner space in which molten iron and scrap iron are received. The vessel 100 is open at its upper side and is provided at its side with a discharge port 110 through which molten steel is discharged. The darts 110 are provided with darts (not shown). The darts are formed in a funnel shape so as to close the lances 110 though a plurality of slots are not shown, And a protrusion connected to a lower portion of the head and inserted into the opening.

Here, the lance 200 is inserted into the furnace of the converter 100, and oxygen for refining the molten iron is taken in. A nozzle (not shown) for injecting an inert gas for stirring the molten steel is inserted into the lower portion of the converter 100.

Referring to FIG. 1, a method of refining a molten iron according to an exemplary embodiment of the present invention includes the steps of completing ironing of molten steel produced in a previous operation (S100), tilting a converter, (S300) of charging the molten iron into the slag remaining in the converter (S300), charging the molten iron to be used in the present ironing process (S400) (S500, S700), and discharging the slag produced by the blowing after the blowing (S600). And the above-described series of steps are repeated and repeated.

In step S100, the molten steel produced during the previous operation is introduced and the molten steel is poured. The amount of the residual slag in the converter 100 at the time point when the molten steel is completely drained, 30 tons.

When ladle is completed, CaO (calcium oxide) is added to the slag to prevent the P ₂ O _{5 from} being blended during stirring of the slag and the slag in the subsequent process, thereby preventing P from being picked up. That is, quicklime is put in order to prevent P ₂ O ₅ from being mixed into molten steel.

Thereafter, the charcoal is pre-refined before removing the S from the furnace before charging it to the converter. At this time, a desulfurizing agent such as CaO or CaC2 is added to perform desulfurization. Further, it is preferable to perform preliminary desiliconization, preliminary desiliconization, and talline operation before loading the charged charcoal into the converter 100.

After the pre-refining is completed, the converter 100 is tilted so as to discharge part of the slag and to retain the remaining part of the slag (S200) before coating the wall of the converter 100. That is, only a part of the slag generated in the previous step is discharged, and then another part of the slag is left in the converter 100 to be used in the present operating process. At this time, the amount of the slag remaining in the converter 100 may be 50% of the amount of slag generated in the previous step. For example, when the amount of the residual slag in the converter 100 at the time of completion of the excavation is 25 to 30 tons, only 12 to 15 tons of slag is left and the remaining slag is discharged.

The reason why 50% of the slag generated in the previous operation is left and discharged is that the slag in the previous operation is controlled to a basicity that makes it easy to remove phosphorus, And the molten iron may be charged after the basicity of the entire slag generated in the previous operation is controlled. However, in the case of using all of the slag in the previous operation, since the amount of the lime CP to be added for controlling the basicity of the slag is increased and it is not easy to control the slag as the amount of the slag is increased, The amount of slag discharged is preferably 50% of the amount of slag generated in the previous operation.

On the other hand, the tilting angle of the converter 100 is adjusted differently according to the number of times of use (old age) of the converter 100, and the tilting angle is decreased as the frequency of use of the converter 100 increases. This is because as the frequency of use of the converter 100 increases, the volume of the converter 100 increases and a dead zone is created in which oxygen does not directly affect the oxygen blowing. That is, as the frequency of use of the converter 100 increases, the refractory on the inner wall of the converter 100 is eroded and the volume of the converter 100 increases. In the case where the converter 100 having a relatively small number of times of use and the converter 100 having a relatively large number of times of use are tilted at the same angle to dispense slag, in the converter 100 having a relatively high frequency of use, (I.e., in the horizontal direction). And the height of the slag is low in the converter (100), which is relatively frequently used. Generally, since the lance 200 is inserted into the center of the converter 100, oxygen is not supplied to the same region as the edge region in the converter 100 at the time of oxygen injection. This area is a dead zone, and as the area of the blind spot increases, the refining efficiency in the process of blowing is lowered. Accordingly, as the frequency of use of the converter 100 increases, the tilting angle is reduced, and the amount of the residual slag is increased to minimize the blind spot.

When the slag is preheated, an additive for controlling the basicity of the slag is introduced into the slag and an aural process is performed (S300). That is, an additive for controlling the basicity of the slag to 4.5 to 5.5 is added, and a lime CP containing 50% or more of burnt lime can be used as the additive.

The lime CP is a raw material formed by the combination of the powder of quicklime generated in the steelmaking process and the solid cement, and the raw material mixture is composed of about 2 to 3% of dolomite dust and 6% of cement based on limestone sludge. That is, the lime CP is a waste generated during the calcination process of the quicklime. In the present invention, the lime CP is introduced into the slag to increase the T.Fe of the slag and increase the talline ratio.

That is, the lime CP is added to the slag remaining in the converter, and then the Fe and O in the slag react with each other to increase Fe ₂ O ₃ . Therefore, the embodiment of the present invention has less tendency to deodorize compared to conventional double-slag operation with deodorization and high-salt operation. The reason for this is that the reaction between Fe ₂ O ₃ and slag generated by the addition of lime CP can reduce the charcoal until the following operation, as the following reaction occurs.

1) In the slag, (Fe2 +) and (O2-) move to the reaction interface

2) Chemical reaction at slag and Fe ₂ O ₃ interface

3) Migration of phosphorus (P ₂ O ₅ ) from the reaction interface to the slag

4) Fe reduced from Fe ₂ O ₃ moves to the slag from the reaction interface

On the other hand, the amount of lime CP to be introduced into the slag is preferably 10 to 15% based on the amount of the remaining slag. For example, when the slag remaining in the slag generated in the previous operation is 15 tons, 2 tons of lime CP is added.

On the other hand, it is preferable that the basicity of the slag is 4.5 to 5.5 in order to easily capture and remove phosphorus in the slag. When the basicity of the slag is less than 4.5, there is a problem in that the basicity is low and the talline ratio is decreased. When the basicity of the slag is 5.5 or more, the viscosity of the slag increases and the fluidity decreases. As a result, the talline ratio decreases.

Since the supply of oxygen is performed using the lance 200 after the lime CP is charged, the increase of T and Fe and the basicity of the slag are in the range of 4.5 to 5.5, so that the CO 2 gas by the oxygen supply during the reaction of Fe ₂ O ₃ -CaO- And the P ₂ O ₅ is used for vaporization talline operation in the slag layer. Therefore, it is possible to maintain the basicity by using the lime CP by increasing the volume of the furnace by P ₂ O ₅ together with the CO gas, (P ₂ O ₅ ), so that phosphorus can be induced to a low level during the primary blowing. Therefore, the stable phosphorus operation of the process lowers the phosphorus content of the slag and the lime CP, so that the pick-up of P in the furnace can be reduced.

The vaporization talline reaction formula of such phosphorus can be represented as follows.

1 / 2O ₂ + 2e = O ^{2 -}

[P] + 4O ₂ - = (PO ^{3 -} ₄ ) + 5e

[P] + 5 / 4O ₂ + 3 / 2O ^{2 -} = (PO ^{3 -} ₄ )

When the addition of the additives and the anatomy are completed, the coating agent and nitrogen are injected into the converter 100, the converter 100 is tilted, and a nitrogen spray coating is performed. At this time, it is preferable that the amount of the coating agent charged into the converter 100 and the nitrogen flow rate injected are determined according to the amount of the residual slag. As the coating agent, at least one of dolomite and dolomite may be used. As described above, the Fe ^{3 +} increased through the saturation process after the lime CP injection before the nitrogen coating increases saturation solubility of the MgO component of the dolomite introduced into the coating, thus facilitating the coating of the hearth.

On the other hand, when CO ₂ gas is generated at the Fe ₂ O ₃ -Slag-dolomite reaction interface after the dolomite introduction in the coating operation, and the viscosity of the slag increases by the tilt and the cooling by the transfer, the CO ₂ gas is picked up into the slag layer It is possible. In this case, even a small amount of gas may not only have a large volume fraction in the slag, but also cause a slag temperature lowering effect due to the CO _{2 generation} heat, so that the viscosity of the slag may be rapidly increased. At this time, when the slag coating is carried out, the viscosity of the optimum slag exhibiting optimum transfer adhesion is about 70 poise, and the temperature range of the slag having such a viscosity value is preferably 1300 to 1350 ° C.

After completing the nitrogen spray coating and residual slag coating, scrap and charcoal are charged into the converter 100 to participate in the present operating process (subsequent operating process after the previous operating process) (S400). At this time, it is preferable that the scrap iron is put into the converter 100 first. This is because, when the molten iron is first put on the liquid slag controlled through the above process, there is a problem that the explosion occurs due to the reaction, so that the scrap is first put on the slag to solidify the slag from the liquid phase, .

When the charging of the scrap iron and the molten iron is completed, the lance 200 is used to blow oxygen (S500, S700). In this embodiment, the primary (S500) and the secondary (S700) , The primary blowing (S500) and the secondary blowing (S700) are performed with a time lag. The refining efficiency is improved by adjusting the height of the lance at the time of the first blowing (S500) and the blowing at the second blowing (S700) and the oxygen blowing flow rate (that is, the blowing flow rate).

First, in the first blowing step (S500), the blowing is performed by soft blowing to lower the depth of the cavity and enlarge the blowing point. For this, in the present invention, the height of the lance 200 (the distance from the bath surface to the end of the lance) is set to, for example, 11.5 to 12.5 and blown in at 30000 Nm3 / hr. And 20% to 30% of the total amount of oxygen injected by the first secondary is taken in the first blowing. In other words, the blowing is performed until the point of 20 to 30% in the entire process of blowing.

As oxygen is blown under these conditions, the desulfurizing agent added to the molten steel, that is, CaO reacts with phosphorus in the molten steel to form P ₂ O ₅ , and the resulting slag moves to the slag layer located on the upper side of the molten bath surface. However, in the primary blowing step according to the embodiment, as described above, oxygen is blown at 30000 Nm3 / hr with the height of the lance 200 being 11.5 m to 12.5 m, the diameter of the burning point is enlarged, Lower. Therefore, the increase of T.Fe can reduce the phosphorus of the slag by 60% or more, and the removal efficiency of phosphorus can be improved. Here, the reason why the diameter of the burning point is enlarged and the depth of the cavity is reduced is to enlarge the surface area where the slag layer reacts with oxygen to increase the temperature of the slag layer, thereby maximizing the reaction efficiency.

On the other hand, the behavior of phosphorus [P] till completion of the primary winding as described above will be described with reference to FIG. At this time, P in FIG. 4 (a) of FIG. 4 shows P in the charcoal, (P) in P Represents the conventional work in which the lime CP input and the saturation work process are not performed, the letter " q " represents the execution of the afterglow operation after the lime CP 1 ton input, and the " lime CP 2 ton input " That is, □ and ○ indicate the behavior of the molten iron P and the molten iron P after the first blowing, after not having an aftertaste, but after having been awakened.

The results of analysis of the molten steel after the completion of the primary refining operation and the result of analysis of the leaning operation and the results of (a) and (b) in which the leaning operation is not performed are almost the same Range of < / RTI > This is because (a) is lowered due to the reaction of T. Fe contained in the slag with CaO in the slag, but after completion of the first tinning, P (i.e., (c) And the phosphorus is lower than that of (a).

On the other hand, the present invention before (前) was some residual a slag generated in the process, by then establishing a converter performs gongchwi and inject additives lime CP which case input control slag by high salt airway slag and by gongchwi Fe ₂ the amount of O ₃ is increased, rather than show the ion ratio ^{(R = Fe 3+ / Fe 2+} ) in the multi-component system containing Fe ^{3 +} ion, so iron oxide in slag, as well as Fe ^{2 +} ion converter slag in quantitative The relationship shown in the graph of FIG. 5 and the following equation can be derived.

Log R = 0.082K-1.9

5, by increasing the slag basicity with the addition of T. Fe and lime CP generated at the time of the awakening, it was shown that the molten iron was controlled by the increase of T.Fe, which is a tallin condition, and the high salt feeding operation by the introduction of lime CP. In this case, K is the slag composition function and shows the amount of lime CP input and the T.Fe at the time of saturation. In addition, R represents the ion ratio of slag, which represents the ion ratio of T. Fe and Fe generated in the operation of the saturation. That is, FIG. 5 shows that the molten iron content can be controlled by comparing the operations of the comparative example and the embodiment.

As described above, the increase of the basicity and the ratio of iron oxide to the residual slag increases with increasing basicity of slag, and the amount of iron oxide increases as the basicity of slag increases.

On the other hand, the graph of FIG. 6 shows the tearing rate and the firing rate of the molten iron according to the primary smelting time when the lime CP is fed after the feeding.

6 (a) shows a talline ratio in which the phosphorus was controlled by the primary smelting time after the lime CP insertion, and FIG. 6 (b) shows the lime CP firing rate according to the smell time. At this time, the lime CP charging rate indicates that the lime CP reacts with the slag to melt phosphorus in the slag when oxygen is supplied.

Therefore, it can be confirmed that the talline ratio and the materialization rate increase with the increase of the winding time by the after-feeding of the lime CP.

Thereafter, when the primary blowing is completed, the converter 100 is tilted to dislodge the slag (S600). This is a slag generated during the primary blowing, and since P is removed from the converter 100 by discharging the slag, it is preferable to discharge a large amount of slag as much as possible. As described above, since the internal volume of the converter 100 is increased according to the frequency of use of the converter 100, it is preferable to increase the tilting angle and remove the slag as the frequency of use of the converter 100 increases.

In the secondary smelting step (S700), the depth of the cavity is formed to be deeper than that at the time of the first blowing so that the blown oxygen can penetrate the slag layer and easily reach the molten iron located at the lower side. To this end, in the present invention, the height of the lance 200 is adjusted to be lower and the oxygen blowing flow rate is increased in the secondary blowing step, as compared with the case of the first blowing. Accordingly, the increase of oxygen in the internal charcoal is favorable compared to the prior art, and the phosphorus removal efficiency is improved. Further, during such secondary blowing, C reacts with the oxygen to be blown in the molten iron, and decarburization proceeds.

At the time when the blowing is advanced by 75% or more during the second blowing, dolomite is put into the furnace (S). At this time, the dolomite is divided into 500 kg units twice, and the hood pressure in the furnace is increased. Therefore, it is possible to prevent the atmosphere from entering the converter in the second half of the second tinning, and to prevent the nitrogen N taken into the outside air from being picked up by the molten iron by hardening the slag layer.

When the secondary blowing is completed, the produced molten steel is introduced into the ladle (S800). In the embodiment, the sediment is fed together with the dolomite to prevent the slag from flowing out during the running. Here, the soaking material may be a material made of paper pulp. When the dolomite and the sediment are introduced during the ladle feeding, the temperature of the slag is lowered and the slag is prevented from boiling. That is, it is possible to prevent the outflow of the slag during the running.

In addition, the number of slots that are opened according to the number of times of use of the converter 100 can be adjusted at the time of touring. For example, when four slots are provided in the dart head, four slots are used when the number of times the converter 100 is used is 60 or less, and three slots are used when the number of times is 100 or more. Reduce.

As described above, a table showing changes in the operating process of the comparative example and the example of the present invention is presented.

division Comparative Example Example Low [P] Control range ≤ 120 ppm ≤ 120 ppm Chartered [P] 1200 to 1500 ppm 1200 to 1500 ppm After first blowing [P] 200 to 320 ppm 110 to 200 ppm End point [O] 850 ppm 650 ppm End point [N] 30 to 40 ppm 20 to 25 ppm

Referring to Table 1, it can be seen that the control range of the phosphorus phosphorus in Comparative Examples and Examples is 120 ppm or less, and phosphorus content in the phosphorus is 1200 to 1500 ppm.

At this time, in the operation of the embodiment, it is possible to increase the content of Fe in the slag by introducing lime CP into the slag generated in the previous operation step before the primary firing of the molten iron and performing an aeration. Therefore, phosphorus can be vaporized before the talline agent is introduced to tannin the phosphorus in the primary blown. Thus, it can be confirmed that the phosphorus after the first blowing is reduced as compared with the comparative example.

Further, it is confirmed that the concentration of the end point nitrogen is lower than that of the comparative example by injecting dolomite into the molten iron after curing to harden the slag layer, thereby preventing the nitrogen introduced into the outside air from penetrating into the molten steel.

As described above, according to the embodiment of the present invention, in refining the charcoal, after 50% of the slag generated in the previous operation is left before charging the charcoal into the converter, the lime CP To control the basicity of the slag, thereby effectively removing phosphorus. That is, the content of Fe in the slag can be increased by introducing and liquefying the lime CP, and the phosphorus content of the molten iron can be easily controlled by increasing the talline ratio of the molten iron by the increased content of Fe.

The amount of CaO (burnt lime) introduced in the tallin process can be reduced by forming an atmosphere in which phosphorus can be efficiently removed before charging the molten iron into the converter. In other words, the phosphorus CP can be partially removed before the molten iron is blown by the lime CP introduced before molten iron charging. By reducing the input amount of quicklime by the amount of the lime CP, the consumption cost due to the input of quicklime can be reduced.

Further, even if the slag is entirely discharged and the process is proceeded in the past, the problem of deviation of the process due to the amount of residual slag and the basicity condition can be solved.

Although the present invention has been described with reference to the accompanying drawings and the preferred embodiments described above, the present invention is not limited thereto but is limited by the following claims. Accordingly, those skilled in the art will appreciate that various modifications and changes may be made thereto without departing from the spirit of the following claims.

100: converter 200: lance
110: Slots

Claims (7)

Completing the tapping of the molten steel produced in the previous operation;
Tilting the converter to exclude a portion of the slag generated in the previous step;
Introducing a lime CP having a CaO content of 50% or more into the slag remaining in the converter, and collecting the same;
Charging a charcoal for use in the present process to the converter;
Culling said charcoal; And
And discharging the slag produced by the blowing after said blowing. delete The method according to claim 1,
Wherein the amount of the slag remaining in the converter in the step of collecting remains within a maximum of 50% of the slag generated in the previous step. The method of claim 3,
And adjusting the basicity of the slag in the converter to not less than 4.5 to not more than 5.5 in the step of adding. The method of claim 3,
Wherein the additive feeds an amount of 10 to 15% of the amount of slag remaining in the converter. The method according to claim 1,
Wherein the step of blowing the charcoal includes a primary chopping process and a secondary chopping process, wherein the primary chopping and the secondary chopping are performed with a time difference. The method according to claim 1,
Wherein the step of charging dolomite to the converter and blowing in an inert gas to coat the inner wall of the converter is carried out prior to charging the charcoal.

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