JP2002256326A - Method for refining molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method with which unit requirement of lime and the amount of discharge of slag to the outside of the system are reduced to the lower limits by reusing the slag and also, only slag having extremely small amount of non-slagging lime can be discharged to the outside of the system. SOLUTION: In a steelmaking method by using two sets of refining furnaces, in which the one side is used for a decarburizing furnace and the other side is used for molten iron dephosphorizing furnace, in the decarburizing furnace, while leaving the whole or a part of the decarburized slag produced in this decarburizing furnace, the decarburize-refining is performed to the molten iron refined in the molten iron dephosphorizing furnace. In the molten iron dephosphorizing furnace, while leaving the whole or a part of the dehosphorized slag produced in this molten iron dephosphorizing furnace, a process for refining a blast furnace molten iron or the molten iron applying a desiliconizing treatment and/or a desulfurizing treatment, is preformed at least one time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for refining molten iron, which promotes the reuse of slag to minimize the amount of slag discharged to the outside of the system, and discharges only slag containing extremely little unslagged lime to the outside of the system. How to make it possible.

[0002]

2. Description of the Related Art Steelmaking methods using hot metal dephosphorization and decarburization using two converters are widely known. For example, JP-A-63-9
Japanese Patent No. 3813 discloses that one of two converter-type furnaces having both upper and lower blowing functions is used as a dephosphorizing furnace and the other as a decarburizing furnace for refining hot metal. Discloses a method of adding converter slag and quick lime generated in a decarburization furnace as main components of a refining agent. However, in this method, it is necessary to cool and solidify the decarburized slag again to add it to the dephosphorization furnace, and to mold the slag. There was a big problem of increasing. Furthermore, although the decarburized slag is in a molten state at 1650 ° C., which is the blowing temperature, in the case of hot metal dephosphorization, it cannot be melted easily because it is about 1350 ° C. Lower than. Furthermore, the decarburized slag rapidly dissolves when the dephosphorization process proceeds and the temperature and the slag composition reach conditions suitable for dissolution. However, since the decarburized slag contains a high concentration of (T.Fe), there is a problem that when the decarburized slag is melted, a decarburizing reaction occurs rapidly, so that slopping frequently occurs.

[0003] In addition, there are several known examples of hot metal dephosphorization using decarburized slag. Japanese Patent Application Laid-Open No. 01-75618 discloses a dephosphorization process in which a desulfurized hot metal is dephosphorized in a dephosphorization furnace and then decarburized in a decarburization furnace to obtain a molten steel product by adding a medium solvent. The low-P converter slag by-produced in the decarburization and refining of pig iron is directly charged into a dephosphorization furnace and reused for dephosphorization and refining.
A method of discharging low free lime and high P converter slag is disclosed. However, this method has not solved the problem. In particular, since the concentration of phosphoric acid in the decarburized slag is low, the concentration of phosphoric acid in the dephosphorized slag after reuse is never concentrated, which is almost the same as the case where the decarburized slag is not reused. Therefore,
It does not open use as a fertilizer that phosphoric acid has.

[0004] Japanese Patent Application Laid-Open No. 05-247511 discloses that when refining hot metal to produce molten steel, hot metal is charged into a converter as a first step, and flux addition and oxygen blowing are performed as a second step. Performing dephosphorization refining to reduce the phosphorus concentration to a predetermined level, as a third step tilting the converter to discharge the slag generated in the second step, and then perform a decarburization step using the same converter to remove the slag There is disclosed a method of tapping steel while leaving it in a converter and recycling the slag to a first step. In this method, although the decarburization slag is recycled in a molten state, the problem due to slag reduction is reduced, but the slag is not sufficiently discharged as the third step, so that the dephosphorization load in the decarburization furnace is large and the slag is removed. There has been a problem that the generated amount does not decrease as a whole, and the concentration of phosphoric acid in the dephosphorization residue is insufficient.

On the other hand, as a method for treating hot metal dephosphorization slag,
For example, JP-A-57-179090 discloses a method of dephosphorizing high-phosphorus iron containing 0.15 to 0.5% of [P] to reduce the phosphoric acid in the produced slag to 15% or more and use it as a phosphate fertilizer raw material. Although disclosed, there is no knowledge about the concentration of phosphoric acid that can be concentrated in slag under the condition of low hot metal [P].

[0006]

SUMMARY OF THE INVENTION The present invention relates to Japanese Patent Application Laid-Open
-93813, JP-A-01-75618, the problem that the amount of slag generated in the dephosphorization furnace is rather increased, and that the dephosphorization efficiency is lower than that in the case of using quicklime. The problem is that the concentration of phosphoric acid in the dephosphorized residue after reuse is not concentrated, and the technology disclosed in Japanese Patent Application Laid-Open No. 05-247511 has
The problem that the dephosphorization load in the decarburization furnace is large due to the inability to sufficiently discharge the slag as the third step, and that the amount of slag generated does not decrease as a whole, and that the concentration of phosphoric acid in the dephosphorization slag is also insufficient. The technology disclosed in Japanese Patent Application Laid-Open No. 57-179090 solves the problem that there is no knowledge about the concentration of phosphoric acid that can be concentrated in slag under low hot metal P conditions. It is an object of the present invention to provide a method that promotes and minimizes the amount of out-of-system discharge to the utmost, and also enables the discharge of only slag with very little unslagged lime out of the system.

[0007]

The gist of the present invention is as follows.
In the way. (1) Two refining furnaces, one furnace for hot metal dephosphorization and the other furnace
In a refining method with a decarburization furnace, and in a hot metal dephosphorization furnace
Is to remove all or all of the dephosphorized slag generated in the hot metal dephosphorization furnace.
Blast furnace hot metal or desiliconization and / or
Or refining hot metal that has been subjected to desulfurization
Is to remove all or part of the decarburized slag generated in the decarburization furnace.
Decarburizing and refining hot metal refined in a hot metal dephosphorization furnace while remaining
Process at least once in both furnaces.
A method for refining molten iron, which is carried out above. (2) In the method of (1), the decarburizing furnace, hot metal dephosphorizing furnace and
Refining of molten iron characterized by using a top-bottom blow converter
Method. (3) In the method of (1) or (2), hot metal dephosphorization
Hot metal dephosphorization furnace while the basicity of the treated slag is 0.7 or more
While leaving all or part of the dephosphorized slag produced in
Blast furnace hot metal without adding quicklime or desiliconization and
Implement operations to refine hot metal that has undergone desulfurization
And when it is lower than 0.7, the dephosphorized slag is completely discharged.
A method for refining molten iron, which is provided. Where basicity
What is CaO concentration in slag and SiO_TwoConcentration percentage of concentration
(CaO / SiO _Two). (4) In any one of the methods (1) to (3),
The [Si] concentration in the hot metal charged to the iron dephosphorization furnace was 0.25 mass
% Or less, the method for refining molten iron. (5) The method according to any of (1) to (4)
In the blowing in the iron dephosphorization furnace, the parameters determined by equation (1)
The molten iron, characterized in that the
Refining method. α = (F / W) × τ / (L / L0) (1) where F is the top blowing acid feeding speed (Nm^Three/ h), W is the mass of molten iron
(T), τ is uniform mixing time (s), L is cavity depth
(m), L0 is bath depth (m). In addition, uniform mixing by bottom blow stirring
The time (τ) is calculated by the following equations. τ = 100 × {(D^Two/ L₀)^Two/ (Ε_B+ Ε_T)}^0.337 ・ ・ ・ ・ (2) ε_B= 371 × (Q / 3600 / W) × T × {ln (1 + 7 × L₀/10.33)+0.06×(1-298/T)} ··· (3) ε_T= 0.134 / W x (F / 3600)^Three× 32 / n^Two/ D^Three/ LG (4) where D is the bath diameter (m) and Q is the stirring gas flow rate (Nm^Three/ h),
T is hot metal temperature (K), n is the number of lance nozzles blown up, d is
Blowing lance nozzle diameter (m), LG is static
It is the distance between the fusible iron surfaces (m). L (m) is calculated by the following equation.
You. L = 63 × (F / (d × 1000) / n)^2/3× exp (−0.78 × LG × 1000 / (63 × (F / (d × 1000) / n)^2/3)) (5) (6) In any one of the methods (1) to (5),
In blowing in a charcoal furnace, decarburized slag is 20 to 40 kg /
Part of the decarburized slag generated in the decarburization furnace so that t
A method for refining molten iron, comprising: (7) In any one of the methods (1) to (6),
The decarburized slag discharged after blowing in the coal furnace is converted to a hot metal dephosphorization furnace.
A method for refining molten iron, characterized by recycling to steel.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, the slag produced by the dephosphorization treatment has a sufficient dephosphorization ability even after a single dephosphorization treatment, and can be used again for the dephosphorization treatment. Based on the finding that there is.

[0009] The hot metal dephosphorization treatment is a non-equilibrium process that occurs between a slag phase having a high (T.Fe) and a high oxygen activity and a molten iron having a low oxygen activity close to carbon saturation. The speed is expressed by equation (6). −d [% P] / dt = (A · k / W) {[% P] −a _PO2.5 ^* / LP} (6) where [% P] is the phosphorus concentration in the hot metal. , T is the time (s), A is the reaction _interface area (cm ² ), k is the overall mass transfer coefficient (cm / s), W is the amount of hot metal (t), and a _PO2.5 is the slag (PO _2.5 ). The activity and LP are equilibrium distribution ratios at the interface, and are determined by the interface concentration indicated by ^* (7)
It is expressed by an equation. ^{_{LP = a PO2.5 * / [%}} P] * = In ^{_{K × a O * 2.5 ··· ...}} (7) where, K is the equilibrium constant, a _O ^* is an interfacial oxygen activity of.

If a _PO2.5 ^* is proportional to the concentration of (PO _2.5 ) in the slag and LP is not sufficiently large, with the increase of the concentration of (PO _2.5 ) in the slag, a Since the _{amount of PO2.5} ^* / LP increases, the dephosphorization rate decreases.

However, according to the detailed study of the present inventors, in the case of hot metal dephosphorization slag, even if the (PO _2.5 ) concentration in the slag changes, a _PO2.5 ^* / LP in the equation (6) is almost _zero ^. Found that it was not affected. This is due to the following two factors.

1) The oxygen activity at the contact interface between the hot metal and the slag in which the reaction occurs is affected by (T.Fe) in the slag, and is larger than the value determined by the equilibrium with the carbon concentration in the bulk hot metal. Therefore, as can be seen from the equation (7), since LP is sufficiently large, a _PO2.5 ^* / LP is always negligibly small even if the (PO _2.5 ) concentration in the slag changes.

2) Even if the (PO _2.5 ) concentration in the slag changes,
(PO _2.5 ) is a surface active component and has the effect of suppressing the nucleation of CO bubbles due to decarburization, and suppresses decarburization during dephosphorization (T.
Fe) can be kept high. For this reason, the oxygen activity at the contact interface between the hot metal and the slag increases with an increase in the (PO _2.5 ) concentration, so that a _PO2.5 ^* / LP does not change at all even if the (PO _2.5 ) concentration in the slag changes. do not do. Here, (T.Fe) indicates the total iron concentration as iron oxide in the slag.

This means that the slag after the dephosphorization treatment has (PO
_{Although 2.5} ) is included, it is the principle that even if it is reused, further dephosphorization is possible.

Further, when dephosphorization slag is used, decarburization during dephosphorization can be suppressed and (T.Fe) can be kept high, so that (PO _2.5 )
In the dephosphorization treatment using dephosphorization slag containing, the decarburization is small, and the heat tolerance in the converter, which is the next step, can be greatly increased.

Claim 1 utilizes this,
In a steelmaking method using two converters, one of which is a hot metal dephosphorization furnace and the other is a decarburization furnace, in the hot metal dephosphorization furnace, the dephosphorization slag generated by the hot metal dephosphorization furnace is entirely or completely removed. The blast furnace hot metal or the hot metal that has been subjected to desiliconization and / or desulfurization treatment is smelted with the remaining part, and in the decarburization furnace, all or part of the decarburized slag generated in the decarburization furnace is retained. A method for refining molten iron, comprising performing at least one or more steps of decarburizing and refining hot metal refined in a hot metal dephosphorization furnace while keeping it.

In the hot metal dephosphorization furnace, as described above, the slag generated by the dephosphorization treatment has a dephosphorization capability based on the principle that the slag has a dephosphorization capacity that can be used for the dephosphorization treatment again. It can be used repeatedly in the phosphorus step.

The dephosphorized slag generated in the hot metal dephosphorization furnace may be left in its entirety, or may be partially discharged and the remaining portion may be left.
Depending on the [Si] concentration of the secondary charged hot metal, SiO ₂
May be generated in a large amount, and the amount of slag may be greatly increased.
Since such a low basicity slag undergoes vigorous slag forming during the dephosphorization treatment, it is better to partially discharge the slag in such a case. When the [Si] concentration of the next charge hot metal is low, the entire amount may be left. Also, lime can be added to suppress the forming and increase the reaction efficiency.

When the slag to which quicklime is added is repeatedly used one or more times without adding new quicklime, FIG.
As shown in (1), the concentration of freeCaO (CaO not dissolved in the slag) in the slag is greatly reduced, and expansion and pulverization, which are problems when using the slag, do not occur.

This is because even if the composition of the slag can be dissolved in the phase diagram, the lump of lime cannot be completely dissolved due to the low dissolution rate. In particular, this is remarkable in the case of low-temperature and short-time treatment such as hot metal dephosphorization refining. To obtain this effect, the number of repetitions is required at least once.

Here, the number of repetitions is defined as follows. Before adding secondary materials such as quicklime, the number of repetitions of refining performed by adding new quicklime while slag refined in the same furnace before the refining does not remain (excluding slag mixed inevitably) 0, and the number of refining repetitions performed using the entire or a part of the slag after the 0 refining is defined as 1. Hereafter, according to this example, it will be twice, three times, and so on.

By separating the decarburizing furnace from the dephosphorizing furnace, it is possible to prevent dephosphorized slag having a high phosphoric acid concentration from being mixed into the decarburizing furnace.
In the decarburization furnace, there is no need to make slag for dephosphorization. Therefore, in a decarburization furnace, the amount of slag can be determined on the condition that the refractory erosion is small and the amount of dust generated does not increase, and since the slag does not contain phosphoric acid, it is basically repeatedly used any number of times. be able to. By repeatedly using the decarburized slag, the amount of newly added lime can be reduced, and the amount of slag generated can also be reduced. To obtain this effect, the number of repetitions is required at least once.

The slag in the decarburization furnace may be left in its entirety, or may be partially drained and the remaining portion may be left. That is, iron ore or manganese ore may be used in the decarburization furnace, and in that case, SiO ₂ , Al ₂ O _{3 and the} like are inevitably mixed from the gangue components, and the amount of slag increases. If the amount of slag becomes too large,
Since the yield of iron decreases, part of the iron ore or manganese ore may be left as it is, and if necessary, the entire amount may be retained if refining is performed without using iron ore or manganese ore. In addition, CaO can be added to compensate for the mixed SiO ₂ .

Claim 2 specifies the type of furnace, and both the decarburization furnace and the hot metal dephosphorization furnace use an upper-bottom blow converter. Here, the reason why the hot metal dephosphorization furnace is the top-bottom blow converter is that the contact interface between the hot metal and slag where the reaction takes place is suspended not by the interface between bulk hot metal and slag but by the energy of top blowing or bottom blowing in the slag. This is because the surface of the turbid molten iron particles is mainly used. In addition, the reason why the decarburization furnace is a top-bottom blow converter is that even if the amount of decarburization slag changes significantly due to repeated use, stable blowing can be achieved by controlling the conditions of top blow and bottom blow. This is because it can be done.

Claim 3 stipulates the conditions for repeatedly performing the dephosphorization slag. The dephosphorization slag after the hot metal dephosphorization treatment has a basicity of 0.7 or more. Repeating the operation of refining the blast furnace hot metal or the desiliconized and / or desulfurized hot metal without adding quicklime, while leaving all or part of the phosphorus slag,
It is to discharge the entire amount of the dephosphorized slag when the value becomes lower than 0.7. The reason for setting the basicity to 0.7 is that if the basicity is lower than 0.7, the activity of phosphoric acid in the slag increases, so that (PO _2.5 ) increases and (T · Fe) increases. This is because a _{PO 2.5} ^* / LP in the equation (6) becomes so large that it cannot be ignored, and as shown in FIG. 2, the dephosphorization rate decreases. When the basicity is 0.7 or more, the dephosphorization ability is sufficiently high, so that it is not necessary to newly add quicklime in the dephosphorization treatment. Generally, every time the dephosphorization process is repeated,
Since [Si] is oxidized and the generated SiO ₂ is accumulated, the basicity decreases with each addition unless quick lime is added. Therefore, in the first dephosphorization blowing without leaving the pre-charge dephosphorization slag, it is desirable to set the basicity to 1.7 to 2.3 and to reduce the basicity as the dephosphorization slag is repeatedly used.

A fourth aspect of the present invention is that the hot metal charged into the hot metal dephosphorization furnace is
The mass percentage of [Si] is set to 0.25% or less. 1 when the [Si] concentration is higher than 0.25%
Since a large amount of SiO ₂ is accumulated in one dephosphorization refining, the number of repetitions is small and inefficient. In this respect, the lower the mass percentage of [Si] in the hot metal, the more efficient, but the [Si] in the hot metal must be reduced in the previous step, and the efficiency of the previous step decreases. Therefore, the lower limit of the mass percentage of [Si] in the hot metal is not particularly defined.

A fifth aspect of the present invention relates to a method of operating a hot metal dephosphorization furnace, wherein the parameter α determined by the equation (1) is set to 30.
This is a method for refining molten iron, characterized in that the melting point is from 0 to 1300. α = (F / W) × τ / (L / L0) (1) where F is the top blowing acid transfer rate (Nm ³ / h), and W is the molten iron mass (t). , Τ is the uniform mixing time (s), L is the cavity depth
(m), L0 is bath depth (m).

The uniform mixing time (τ) by bottom-blowing agitation is calculated by the following equations. τ = 100 × {(D ² / L ₀ ) ² / (ε _B + ε _T )} ^0.337 (2) ε _B = 371 × (Q / 3600 / W) × T × {ln (1 + 7 × L ₀ /10.33)+0.06×(1-298/T)} (3) ε _T = 0.134 / W × (F / 3600) ³ × 32 / n ² / d ³ / LG (4) where D is the bath diameter (m), Q is the stirring gas flow rate (Nm ³ / h),
T is the hot metal temperature (K), n is the number of upper blowing lance nozzles, d is the diameter of the upper blowing lance nozzle (m), and LG is the distance between the tip of the upper blowing lance and the stationary molten iron surface (lance gap; m).

L (m) is calculated by the following equation. L = 63 × (F / (d × 1000) / n) ^2/3 × exp (−0.78 × LG × 1000 / (63 × (F / (d × 1000) / n) ^2/3 )) (5)

The parameter α is an index representing the rate of FeO generation by top-blown oxygen according to the acid feeding rate and the cavity depth, and is an index representing the rate of reduction of FeO by hot metal in a uniform mixing time. (T.Fe) in the inside becomes high. Therefore, even if the dephosphorized residue is repeatedly used, a _PO2.5 / LP in the equation (6) is easily kept small, which is advantageous. As shown in FIG. 3, if α is smaller than 300, ( _T.Fe ) in the slag cannot be kept high, so that a _PO2.5 / LP in the equation (6) cannot be kept small, and the dephosphorization slag is repeated. Infrequent use. Conversely, if it is larger than 1300, (T
・ Fe) becomes too high, causing operation failure due to slopping.

The parameter α can be controlled from 300 to 1300 by controlling the acid feed rate, molten iron mass, uniform mixing time, lance height, cavity depth, and bath depth.

Claim 6 defines conditions in the decarburizing furnace, and in blowing in the decarburizing furnace, the decarburized slag is 20 to 40%.
A part of the decarburized slag generated in the decarburization furnace is discharged to 40 kg / t. Here, the unit of kg / t is slag weight (kg) per ton of hot metal. The hot metal weight (t) at this time uses the weight of the hot metal to be charged into the decarburization furnace in the next process.

When the decarburized slag is less than 20 kg / t, the amount of dust generated is large and the yield is reduced, and the concentration of (T.Fe) in the slag is liable to increase and the refractory erosion is likely to increase. Conversely, if it is more than 40 kg / t,
It is not economical because iron loss and Mn loss in slag increase.

A seventh aspect is a method of recycling decarburized slag discharged after blowing in a decarburizing furnace to a hot metal dephosphorizing furnace. The decarburized slag produced in the present invention contains little (PO _2.5 ), and generally has a basicity of 3 or more and has a high (T · Fe). It has sufficient dephosphorization ability even when reused. Therefore, the slag discharged from the decarburization furnace, once cooled and solidified, or by recycling to hot metal dephosphorization furnace while hot,
The use of fresh quicklime can be greatly reduced. In particular, in the operation described in claim 3, if the decarburized slag is used in the first blowing after removing all the dephosphorized slag, the dephosphorizing operation can be always performed without using fresh quicklime.

[0035]

EXAMPLES Examples were carried out using a 280 ton scale top-bottom blow converter. Top blow lance of hot metal dephosphorization furnace is 7 of 46φ
The oxygen supply rate was 20,000 Nm ³ / h using a hole lance,
The lance gap was set to 2.4 to 2.6 m. Bottom blowing was the CO ₂ and small collecting pipe tuyere to 1200 Nm ³ / h feed. Under this condition, the parameter α is 850 to 900.

The composition of the pre-desulfurized blast furnace hot metal charged in the hot metal dephosphorizing furnace is as follows: C: 4.35 to 4.65%, Si:
0.1 to 0.2%, Mn: 0.23 to 0.35%, P: 0.2%
095 to 0.110%, S: 0.009 to 0.014%
And the temperature was 1325 to 1365 ° C. The dephosphorization refining time was about 9 minutes, and during the dephosphorization, iron ore was charged from the upper bunker at 10 to 16 kg / t for temperature control. After the treatment, C: 4.05 to 3.8%, Si: 0.02% or less, Mn:
0.03 to 0.08%, P: 0.019 to 0.028%,
S: 0.010 to 0.015%, temperature is 1345 to 136
5 ° C.

The results are shown in Table 1. In the first hot metal dephosphorization treatment, the hot metal and the scrap were charged into a hot metal dephosphorization furnace, and 11.2 kg / l of quicklime was added to the iron ore during blowing. t was added. After the completion of the first hot metal dephosphorization treatment, the furnace was tilted to discharge hot metal, and then the next charge of blast furnace hot metal and scrap were charged while leaving the entire hot metal dephosphorization slag in the furnace. During the blowing after the next charge, quicklime was not added. Repeated use blowing was carried out five times with the entire amount of dephosphorized slag remaining. As a result, the basicity of the slag became lower than 0.7. At that time, the entire amount of dephosphorized slag was discharged. As can be seen from Table 1, during this period, good dephosphorization behavior was obtained without using quicklime. Since quicklime was used only at the first charge, hot metal (280 (t) x 6 (c
h. )) To 3136 kg of lime (11.2 (kg
/ T) × 280 (t)), and the basic unit through 6ch is (280 × 11.2) /
(280 × 6) = 1.87 kg / t.

[0038]

[Table 1]

As a result of blowing 6 charges by repeating 5 times, the amount of slag generated outside the furnace was only 49.1 kg / t, and the amount of slag generated outside the furnace was 8 with the total amount of dephosphorized hot metal treated as a denominator. It was only .2kg / t. In addition, since quicklime introduced in the first charge can be sufficiently dissolved in slag during repeated use, free lime in slag generated outside the furnace is free.
CaO was as low as 0.1% or less.

The hot metal after the above-mentioned dephosphorization treatment was successively charged into a decarburization furnace and treated. The top blowing lance of the decarburization furnace is 46
Oxygen supply rate is 45000Nm ³ / h using φ 5 hole lance
And Bottom blowing the 1200N the CO ₂ and the small-diameter collecting pipe tuyere
m ³ / h.

During the decarburization and refining of the dephosphorized hot metal repeated 0 times, no slag from the previous refining remained in the decarburization furnace, and 8 kg / t of quicklime and 7 kg / t of iron ore were charged from the upper bunker. . After the decarburization refining, dephosphorized hot metal of the next charge (the above-mentioned repetition number 1) was charged while leaving the entire amount of the decarburized slag without discharging. Similarly, after the decarburization refining, the above-mentioned dephosphorization of the dephosphorized hot metal was repeated 5 times while leaving the entire amount of the decarburized slag without discharging. In the decarburization blowing of the dephosphorized hot metal after one repetition, the addition amount of iron ore was 5 to 8 kg / t, and the addition amount of quicklime was 0 to 3 kg / t to compensate for the gangue component. .

The decarburization time is about 12 minutes. After the treatment, C: 0.15 to 0.35%, Si: 0.01% or less, M:
n: 0.03-0.06%, P: 0.015-0.023
%, S: 0.010 to 0.015%, and the temperature is 1635 to 1
665 ° C.

Five times of repeated use blowing was performed with the entire amount of decarburized slag remaining. As a result, the amount of slag became larger than 40 kg / t, and half of the slag was discharged. During this time, the amount of dust generated was as small as about 20 kg / t,
e) was also as low as 15 to 25%. Furthermore, the quicklime unit consumption averaged 6 charges was 3.3 kg / t, and the amount of slag generated outside the furnace averaged 6 charges was only 3.7 kg / t. Further, as in the case of hot metal dephosphorization, quicklime can be sufficiently dissolved in slag during repeated use, so that freeCaO in slag generated outside the furnace was extremely low at 0.1% or less.

Further, the decarburized slag which was repeatedly used in the decarburization refining for 5 times and the half amount of the decarburized slag was charged into the dephosphorization furnace while being hot was used as a secondary material for the dephosphorization refining of 0 times. . As a result, refining equivalent to the above-described dephosphorization refining of 0 times could be performed without using fresh quicklime.

(Comparative Example) The comparative example also has the same conditions as those of the embodiment.
The test was performed using an 80-ton scale top-bottom blow converter. In the comparative example, the entire amount of slag after hot metal dephosphorization was always discharged, but as a result, since quicklime was used for all charges, the basic unit of quicklime was as large as 11.2 kg / t. In addition, since slag was discharged every charge, the amount of slag generated outside the furnace was as large as 20.4 kg / t. Also, quick lime cannot be sufficiently dissolved in slag during the dephosphorization smelting for 9 minutes.
freeCaO was as high as 3.8%. Even in the decarburizing furnace, the slag after treatment was discharged as a whole with every charge, so quick lime was required for every charge, and the unit of quick lime was 8.5 kg /
There were many with t. In addition, since slag was discharged every charge, the amount of slag generated outside the furnace was as large as 20.3 kg / t. Furthermore, quicklime could not be sufficiently dissolved in slag, and freeCaO in slag generated outside the furnace was as high as 2.1%.

[0046]

According to the present invention, it is possible to minimize the amount of quicklime and the amount of slag discharged outside the system to the utmost by recycling slag, and to discharge only the slag with very little unslagged lime out of the system. It became.

[Brief description of the drawings]

Fig. 1 Number of repeated use of quicklime-added slag and freeCa
Experimental results showing the relationship between O concentrations.

FIG. 2 is an experimental result showing the relationship between the basicity and the dephosphorization rate in the dephosphorization treatment.

FIG. 3 shows the effect of parameter α on the relationship between the number of repetitions and the dephosphorization rate in the dephosphorization treatment.

Continued on the front page (72) Inventor Naoto Sasaki 20-1 Shintomi, Futtsu Nippon Steel Corporation Technology Development Division F term (reference) 4K014 AA03 AB03 AB04 AC03 AC11 AC16 AC17 AD00 AD27 AE01 4K070 AA10 AB03 AB06 AB11 AC03 AC13 AC14 BA07 BA10 BB02 BB05 BC02 BC12 BD13 BD14 BD15 EA01 EA03 EA30

Claims (7)

[Claims] 1. A refining method using two refining furnaces, one of which is a hot metal dephosphorization furnace and the other of which is a decarburization furnace, wherein the hot metal dephosphorization furnace comprises dephosphorization produced by the hot metal dephosphorization furnace. The blast furnace hot metal or the hot metal that has been subjected to desiliconization and / or desulfurization treatment is refined while leaving all or part of the slag, and in the decarburization furnace, the total amount of decarburized slag generated in the decarburization furnace is A method for refining molten iron, characterized in that the step of decarburizing and refining hot metal refined in a hot metal dephosphorization furnace while leaving a part thereof is performed at least once in both furnaces. 2. The method of claim 1, wherein the hot metal dephosphorization furnace comprises:
A method for refining molten iron, characterized in that both decarburization furnaces and top-bottom blow converters are used. 3. The method according to claim 1 or 2, wherein the dephosphorized slag produced in the hot metal dephosphorization furnace is entirely or partially left as long as the basicity of the slag after the hot metal dephosphorization treatment is 0.7 or more. The blast furnace hot metal or the hot metal that has been desiliconized and / or desulfurized is refined without adding quicklime, and when it becomes lower than 0.7, the entire amount of dephosphorized slag is discharged. A method of refining molten iron. 4. The method according to claim 1, wherein the [Si] concentration in the hot metal charged into the hot metal dephosphorization furnace is 0.2.
A method for refining molten iron, characterized in that the content is 5% by mass or less. 5. A method for refining molten iron according to any one of claims 1 to 4, wherein in the blowing in the hot metal dephosphorization furnace, the parameter α determined by the equation (1) is set to 300 to 1300. . α = (F / W) × τ / (L / L0) (1) where F is the top blowing acid transfer rate (Nm ³ / h), and W is the molten iron mass (t). , Τ is the uniform mixing time (s), L is the cavity depth
(m), L0 is bath depth (m). 6. The method according to claim 1, wherein the decarburized slag is 20 to 40 in blowing in a decarburizing furnace.
A method for refining molten iron, which comprises discharging a part of the decarburized slag generated in the decarburization furnace so as to obtain kg / t. 7. The method for refining molten iron according to claim 1, wherein the decarburized slag discharged after blowing in the decarburization furnace is recycled to a hot metal dephosphorization furnace. .