JP2023001041A - Refining method - Google Patents

Abstract

To provide a refining method for preventing the lowering of a yield of hot metal in a refining process including intermediate slag discharging in a converter-type refining furnace.SOLUTION: A refining method for desiliconizing and dephosphorizing hot metal 2 in a converter-type refining furnace 1, includes a charging process for charging at least hot metal 2 into the converter-type refining furnace 1, a desiliconizing process for desiliconizing the hot metal by feeding oxygen to the hot metal, a slag discharging process for tilting the converter-type refining furnace 1 to discharge slag 4 after the desiliconizing process, and a dephosphorizing process for dephosphorizing the hot metal 2 by feeding oxygen to the hot metal after the slag discharging process. In the charging process, when an internal volume of the converter-type refining furnace 1 is V(m3), an amount of raw pig iron M(t) charged into the converter-type refining furnace 1 satisfies formula (1). V/M≥0.55...(1)SELECTED DRAWING: Figure 1

Description

The present invention relates to a refining method.

In the refining process using a converter-type refining furnace (also called a "converter"), the molten iron undergoes refining reactions such as desiliconization → dephosphorization → decarburization, and molten steel is generated. In such a refining process (steelmaking process), conventionally, a steelmaking process ( Two types of refining methods have been implemented: a steelmaking process using two converters) and a steelmaking process in which desiliconization to decarburization are performed in a single converter (steelmaking using a single converter). there is

Of these, in the steelmaking process using two converters, it is necessary to charge the converters two or more times until the molten steel is made, which increases the heat loss. Flux usage can be reduced. On the other hand, in the steelmaking process using a single converter, only one charge is required until the molten steel is produced. be. Both of these refining processes have advantages and disadvantages, and appropriate methods are selected and implemented depending on the environment such as the production capacity of the pre- and post-processes and the layout of the ironworks.

In addition, in recent years, in both steelmaking processes described above, a refining method has been proposed in which blowing is interrupted after the desiliconization process is completed, slag is intermediately discharged, and the subsequent dephosphorization reaction efficiency is increased (for example, patent Reference 1). In the method disclosed in Patent Document 1, the slag formed (expanded) in the intermediate waste is discharged from the throat of the converter until the hot metal begins to flow out. At this time, the higher the slag discharge rate (%) (=discharged slag amount (t) / slag amount (t) before slag discharge × 100), the higher the CaO concentration in the slag / The amount of flux required to increase the SiO ₂ concentration ratio (also referred to as “basicity”) can be reduced.

JP 2013-167015 A

By the way, in the treatment method described in Patent Document 1, it is required to increase the basicity of the slag in the dephosphorization treatment after the intermediate waste. If an attempt is made to increase the amount of intermediate waste in order to reduce the amount of lime-based flux to be added in the treatment, the amount of hot metal flowing out increases, resulting in a problem of reduced hot metal yield.

SUMMARY OF THE INVENTION An object of the present invention is to provide a refining method capable of preventing a decrease in the yield of hot metal in a refining process involving intermediate slag in a converter type refining furnace.

According to one aspect of the present invention, in a refining method in which hot metal is subjected to desiliconization treatment and dephosphorization treatment in a converter type refining furnace, a charging step of charging at least the molten iron into the converter type refining furnace; , a desiliconization step of performing desiliconization treatment by sending oxygen to the hot metal, a slag removal step of discharging slag by tilting the converter-type refining furnace after the desiliconization step, and the slag removal step. and a dephosphorization step in which ^{dephosphorization} is performed by supplying oxygen to the molten pig iron. , a refining method is provided in which the raw pig iron charging amount M(t) into the converter type refining furnace 1 is an amount that satisfies the formula (1).
V/M≧0.55 (1)

According to one aspect of the present invention, there is provided a refining method capable of preventing a decrease in the yield of hot metal in a refining process involving intermediate slag in a converter-type refining furnace.

It is a mimetic diagram showing a converter type refining furnace in a desiliconization process or a dephosphorization process in this embodiment. It is a schematic diagram which shows a converter type refining furnace in a tailings process. It is a graph which shows the result of an Example.

The following detailed description describes embodiments of the invention with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals, and overlapping descriptions are omitted. Each drawing is schematic and may differ from the actual one. Further, the embodiments shown below are examples of apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is based on the material, structure, arrangement, etc. of the component parts. It is not specific to the following. The technical idea of the present invention can be modified in various ways within the technical scope defined by the claims.

In the refining method according to one embodiment of the present invention, in a converter-type refining furnace 1 as shown in FIGS. Siliconization and dephosphorization are performed. As shown in FIG. 1, oxygen is supplied to the molten iron 2 by blowing oxygen gas into the converter smelting furnace 1 from a top blowing lance 3 while the throat 10 of the converter smelting furnace 1 is set upright. It is performed by supplying to hot metal 2 inside. Further, the desiliconization treatment and the dephosphorization treatment performed in the converter type refining furnace 1 are also collectively referred to as preliminary treatment.

In this embodiment, first, the molten iron 2 is charged into the converter type refining furnace 1 (charging step). In the charging step, the slag after the dephosphorization treatment (also referred to as "post-dephosphorization treatment slag") generated in the previous preliminary treatment of the hot metal 2 remains in the converter-type refining furnace 1, and is charged. New hot metal 2 may be charged from the ladle, or hot metal 2 may be charged after a cold iron source such as iron scrap is charged before the hot metal is charged. The cold iron source to be charged in advance may be iron scrap specified in the "Iron Scrap Acceptance Inspection Standards" of the Japan Iron Source Association, direct reduced iron, cold iron, or other iron-based material. In the iron and steel refining process using the converter type refining furnace 1, the cold iron source melts soon after being charged into the furnace and becomes the hot metal 2, so the weight of the charged hot metal (also called "hot metal weight" The sum of l) and the weight of the cold iron source (also referred to as the "cold iron source amount") is expressed as the raw pig iron charging amount. The molten pig iron charged into the converter type refining furnace 1 and the cold iron source are collectively referred to as raw pig iron.

Further, in the charging step, the raw pig iron charging amount M(t) is set to an amount that satisfies the formula (1), where V(m ³ ) is the internal volume of the converter type refining furnace 1 .
V/M≧0.55 (1)

After the charging step, oxygen is supplied to the hot metal 2 charged into the converter type refining furnace 1 to perform a desiliconization treatment to oxidize and remove silicon contained in the hot metal 2 (desiliconization step). In the desiliconization step, desiliconization is performed by supplying oxygen gas to the hot metal 2 through the top-blowing lance 3 . At this time, auxiliary raw materials such as a silicon source and a lime-based flux may be added to the converter-type refining furnace 1 . In addition, slag 4 generated in the desiliconization process is accommodated in the furnace of the converter-type refining furnace 1 where the desiliconization treatment has been completed in the desiliconization process. The slag 4 includes post-dephosphorization slag charged in advance, auxiliary raw materials charged, SiO ₂ generated by desiliconization, and the like.

After the desiliconization step, intermediate waste is performed to discharge the slag 4 stored in the furnace of the converter type refining furnace 1 to the outside of the furnace (slag discharge step). In the slag removal process, as shown in FIG. 2, the slag 4 is discharged from the furnace throat 10 of the converter smelting furnace 1 by tilting the converter smelting furnace 1 . Moreover, it is preferable that the slag removal process be finished just before the outflow of the hot metal 2 occurs. Since the slag 4 has a lower specific gravity than the molten iron 2 and floats on the molten iron 2 , it flows out of the furnace throat 10 earlier than the molten iron 2 due to the tilting of the converter-type refining furnace 1 . However, when the thickness of the slag 4 becomes smaller, as shown in FIG. 2, the molten iron 2 is caught in the slag 4 by the shear stress from the slag flow generated at the slag-hot metal interface, causing the molten iron 2 to flow out. In addition, the closer the level of the throat 10 where the slag 4 flows out to the slag-hot metal interface, the greater the shear stress. ) is reduced to a certain thickness, hot metal flows out. Therefore, in the slag discharging process, it is not possible to flow out the entire amount of the slag 4 without flowing out the hot metal 2 .

Here, the thickness of the residual slag in the furnace when outflow of the hot metal 2 occurs due to shear stress is almost constant for each charge (processing unit), although it varies in units of several millimeters. Therefore, by reducing the specific gravity of the slag 4, the amount of slag in the furnace at the time when the hot metal 2 begins to flow out can be reduced. For this reason, a method of intentionally forming the slag 4 before starting the slag treatment to reduce the specific gravity of the slag 4 is generally performed. The forming of the slag 4 is adjusted by adjusting the CO gas generation rate, which controls the forming, by changing the oxygen supply rate (Nm ³ /h) and the oxygen supply amount (Nm ³ ).

However, if the slag 4 is formed to fill the entire region of the converter internal volume V other than the volume occupied by the hot metal 2, the converter smelting furnace 1 will not be able to form further if the slag 4 is formed. The slag 4 overflows from the furnace throat 10 of the furnace, causing a problem of damage to peripheral equipment. Therefore, the specific gravity of the slag 4 cannot be lowered below a certain level.

In addition, in the dephosphorization step, which will be described later, it is required to increase the basicity, which is the ratio of CaO concentration/SiO ₂ concentration in the slag. However, since the basicity of the slag 4 generated in the desiliconization process is low, if an attempt is made to increase the amount of intermediate slag in order to reduce the amount of lime-based flux added in the dephosphorization process, the outflow amount of the hot metal 2 due to shear stress will increase. The problem arises that the yield of the hot metal 2 is lowered.

However, in this embodiment, in the charging step, by charging the molten iron 2 so as to satisfy the formula (1), a large amount of slag 4 can be discharged while suppressing the outflow of the molten iron 2 . When the value of V/M in equation (1) is small, the raw pig iron charging amount M is relatively large with respect to the internal volume V of the converter. Sometimes, the space in the converter-type refining furnace 1 other than the raw pig iron becomes smaller. Therefore, slopping, which is a phenomenon in which the slag 4 and the metal (hot metal 2) are blown up from the furnace throat 10 and flow out of the furnace, is likely to occur. In order to suppress this slopping, it is necessary to suppress the forming of the slag 4, and as a result the specific gravity of the slag 4 cannot be sufficiently reduced. Therefore, when the slag 4 is discharged, the mass of the slag 4 remaining in the furnace becomes large when the converter-type refining furnace 1 is tilted to the limit angle where the hot metal 2 does not flow out due to shear stress. .

On the other hand, when the value of V/M in the formula (1) is large, the space other than the raw pig iron in the converter-type refining furnace 1 becomes large when the forming is performed to the very limit of slopping. The specific gravity of 4 can be made smaller. That is, the mass of the slag 4 remaining in the converter-type refining furnace 1 can be reduced, and the dephosphorization characteristics in the subsequent dephosphorization treatment can be improved. As a result, the amount of refining flux and the amount of slag that are required in the decarburization process are reduced, so that the slag loss of the hot metal 2 is reduced. Therefore, the yield of hot metal in the converter process is improved. In addition, since the amount of hot metal 2 caught in the slag 4 (also referred to as “siliconization slag”) discharged as intermediate slag can be reduced, the iron content can be separated when reusing the siliconization slag. It is possible to omit labor such as the above, and it is possible to save labor and cost in the entire steelmaking process.

Incidentally, since the yield of the hot metal 2 is improved, the larger the value of V/M in the formula (1), the better. However, when the value of V/M is large, the amount of hot metal 2 to be processed in the converter-type refining furnace 1 is small, so there is a possibility that the productivity will be lowered. Practically, it is preferable to operate with a V/M of about 0.9 or less, more preferably about 0.8 or less. Furthermore, as M decreases, the proportion of bare metal that adheres to the inside of the furnace increases, and the proportion of iron that is lost in the slag increases. Therefore, V / M is more preferably less than 0.75, and more preferably. is less than 0.60.

After the slag removal step, oxygen is fed to the hot metal 2 charged into the converter-type refining furnace 1 to perform a dephosphorization treatment to oxidize and remove phosphorus contained in the hot metal 2 (dephosphorization step). . In the dephosphorization process, dephosphorization is performed by supplying oxygen gas to the hot metal 2 through the top-blowing lance 3 . At this time, a lime-based flux is added to the converter type refining furnace 1 . Moreover, in the dephosphorization step, slag 4 is produced by the added lime-based flux and the desiliconization slag remaining in the furnace. The slag 4 generated in the dephosphorization step is also called dephosphorization slag.

By going through the above steps, desiliconization and dephosphorization, which are preliminary treatments of the hot metal 2, are performed. After the pretreatment by the converter-type refining furnace 1, molten steel is manufactured by decarburizing the molten iron 2 that has undergone the pretreatment. At this time, after the hot metal 2 is discharged from the pretreated converter refining furnace 1, the decarburization treatment may be performed in another converter refining furnace. A decarburization process may subsequently take place in the furnace 1 .

Although the invention has been described with reference to particular embodiments, it is not intended that the invention be limited by these descriptions. Along with the disclosed embodiments, other embodiments of the invention, including various modifications, will be apparent to persons skilled in the relevant art(s) upon reference to the description of the invention. Therefore, the embodiments of the invention set forth in the claims should be construed to cover the embodiments that include these variations described herein singly or in combination.

For example, in the above-described embodiment, in the desiliconization treatment and the dephosphorization treatment, oxygen gas is supplied from the top-blowing lance 3 to supply oxygen gas, but the present invention is not limited to such an example. For example, in addition to the top-blowing lance 3 , oxygen gas may be supplied from a bottom-blowing tuyere provided at the bottom of the converter-type refining furnace 1 .

An example conducted by the present inventors will be described. In the example, in a converter type refining furnace 1 with a design processing capacity of 350 t/charge, pretreatment of hot metal 2 performing intermediate slag was repeatedly performed from a state in which refractories in the furnace were repaired (at the start of use). rice field. Since the converter internal volume V of the converter type refining furnace 1 increases due to the wear of the refractory as the refining process is repeated, the profile of the bricks in the furnace is measured every 10 charges, and the change in the converter internal volume V is measured. I got it. Further, the converter smelting furnace 1 was used to perform only the preliminary treatment of the above embodiment, and the decarburization treatment was performed in another converter smelting furnace.

In the slag removal process in each charge, the converter type refining furnace 1 was tilted to remove the slag from the furnace throat 10, and the slag was removed just before the hot metal 2 began to flow out. However, in the case of a steel type with a low final phosphorus concentration required in the next dephosphorization step, the amount of lime-based flux to be added is reduced in order to increase the basicity of the slag 4 generated in the dephosphorization step. For this purpose, operations were performed to increase the amount of slag as much as possible.

Results of these operations are shown in FIG. The horizontal axis of FIG. 3 is "converter internal volume V (m ³ )/raw material pig iron charging amount M (t)". The raw pig iron charging amount is the sum of the cold iron source amount (t) charged into the converter in the charging process and the molten pig iron weight (t), as in the above embodiment. The vertical axis in FIG. 3 represents the hot water yield index. The tapping yield index is a numerical value obtained by "amount of molten steel after decarburization refining S(t)/amount of raw pig iron charge M(t)", and the larger the numerical value, the higher the yield.

In the examples, the value of the internal volume V of the converter obtained for each charge was used from the change in the profile obtained from the measurement performed for every 10 charges. The raw pig iron charging amount was calculated from the actual charging amount in each charge. Therefore, these calculations include the burnt residue of impurities that are normally removed in the converter smelting furnace 1, but since there is little variation between charges, they are allowed to be included in the numbers.

As shown in FIG. 3, when the converter internal volume V (m ³ )/raw pig iron charging amount M (t) falls below 0.55, the yield rapidly decreases. From this result, it was confirmed that a high iron yield can be maintained by setting the raw pig iron charging amount M to the converter type refining furnace 1 to an amount that satisfies the formula (1).

1 converter type refining furnace 10 throat 2 hot metal 3 top blowing lance 4 slag

Claims (2)

In a refining method in which hot metal is desiliconized and dephosphorized in a converter type refining furnace,
a charging step of charging at least the molten iron into the converter-type smelting furnace;
a desiliconization step of desiliconizing by sending oxygen to the hot metal;
After the desiliconization step, a slag discharge step of tilting the converter-type refining furnace to discharge slag;
After the slag removal step, a dephosphorization step of dephosphorizing by sending acid to the hot metal;
with
In the charging step, when the internal volume of the converter-type refining furnace is V (m ³ ), the raw pig iron charging amount M(t) into the converter-type refining furnace 1 is given by (1 ) is a refining method that satisfies the formula.
V/M≧0.55 (1) In the charging step, a cold iron source is added in addition to the hot metal,
2. The refining method according to claim 1, wherein said raw pig iron charge amount M is the sum of the charged molten pig iron weight and the cold iron source amount.

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