JP7243414B2 - Hot metal refining method - Google Patents

Description

The present invention relates to a method for refining hot metal.

In recent years, using a converter, hot metal pretreatment (one or more of de-Si, de-P, and de-S), intermediate waste, refining (de-P and de-C), and tapping are performed in a series of processes. A MURC (Multi-Refining Converter) method has been proposed in which . In the MURC process, slag control during blowing for hot metal pretreatment requires a blowing technique for forming slag to the extent that a sufficient amount of slag can be secured while suppressing slopping due to excessive forming.

Generally, as in the method described in Patent Document 1, it is said that the degree of oxidation of slag can be adjusted by controlling the top blowing conditions, and from the concept of slag control, the top blowing conditions during blowing are defined. ing.

Japanese Patent No. 4150272

An object of the present invention is to provide a hot metal refining method that can avoid slopping in hot metal pretreatment and ensure an appropriate amount of intermediate slag.

A method for refining molten iron according to one aspect of the present invention includes a first step of charging molten iron and scrap as main raw materials into a converter, and blowing oxygen into the converter by top blowing and bottom blowing to refining the molten iron. A second step of performing deC and any one or more of deSi , deP, and desulfurization of the hot metal, a third step of discharging slag generated in the converter, and the conversion and a fourth step of blowing oxygen into the furnace by top blowing and bottom blowing to deP and deC the molten iron.
The weight percent concentration of Si in the main raw material charged in the first step is 0.20 or more and 0.80 or less, and the temperature of the hot metal at the end of blowing in the second step is 1200 ° C. or higher. , 1450 ° C. or less, the weight percent concentration of C in the hot metal at the end of blowing in the second step is 3.00% or more, and the CaO and SiO in the slag discharged in the third step The weight ratio of ₂ is 0.6 or more and 2.5 or less.
The second step is performed so as to satisfy the following formula (1).
3.60≦g×Q _t ′/S−0.60×ε _b ≦4.90 (1)
however,
g is the gravitational acceleration [m/s ² ];
Q _t ' is the surplus oxygen amount [kNm ³ /hr] that does not contribute to decarbonization in top blowing;
S is the surface area of the hot metal (volume inside the converter/height inside the converter) [m ² ],
ε _b is the bottom-blowing agitation power density [kW/t].

According to the hot metal refining method according to an aspect of the present invention, it is possible to secure an appropriate amount of intermediate slag while avoiding slopping in hot metal pretreatment.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the refining method of the hot metal which concerns on one Embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical cross-sectional view of a furnace body of a converter for carrying out a method for refining molten iron according to an embodiment of the present invention; 4 is a graph showing the relationship between decarburization oxygen efficiency η and reciprocal 1/ε _t of top-blown stirring power density. 1 is a longitudinal sectional view of a converter for carrying out a method for refining molten iron according to an embodiment of the present invention; FIG. Fig. 3 is an enlarged vertical cross-sectional view of a main portion of a portion on the tip side of the top blowing lance; It is a graph which shows this experiment result.

An embodiment of the present invention will be described below.

(Trigger and idea of the present invention)
The present inventors tried to change the top and bottom blowing conditions for the purpose of improving the yield of the refining process. Specifically, the top-blowing conditions were set with reference to the findings in the method described in Patent Document 1.
However, operational problems such as the induction of slopping occurred. Therefore, we worked to solve this problem.
Here, as a clear difference between the method described in Patent Document 1 and the present approach, the size of the bottom-blowing stirring power was mentioned. Then, the inventors of the present invention considered that the method described in Patent Document 1 does not meet the conditions of a weakly stirred converter.
Accordingly, the present inventors conducted extensive studies and came up with the idea that in the MURC method, the proper blowing range due to the adjustment of the top-blowing conditions varies according to the bottom-blowing conditions.
Then, from the results of the actual machine test, the optimum blowing range was identified by adjusting the top blowing and bottom blowing conditions.

(Mechanism of the present invention)
The slag forming phenomenon in the converter is as follows: 1. "Slag Properties";2. Occurs when the conditions for the "gassing reaction" reach the forming conditions.
In general, it is believed that slag with a high concentration of iron oxide is produced and the slag tends to form when the generation rate of carbon monoxide gas is high.
As a way of thinking about adjustment of the top-blowing conditions for refining in a converter, soft blowing that lowers the impingement dynamic pressure of the top-blown oxygen jet on the hot metal surface reduces the efficiency of oxygen contributing to the combustion of hot metal components, resulting in surplus oxygen. Burns nearby iron to form iron oxide, which facilitates slag foaming.
Further, when hard blowing is performed to increase the impact dynamic pressure of the top-blown oxygen jet, the generation of iron oxide in the slag is suppressed.
On the other hand, the bottom-blowing stirring power has a dominant influence on the stirring of the hot metal in the converter. The concentration of iron oxide in the slag decreases.
Considering the above metallurgical blowing characteristics, it can be said that the conditions under which iron oxide is likely to be generated are soft blowing and weak stirring, and the conditions under which iron oxide is not easily generated are hard blowing and strong stirring.
In order to control the slag foaming state in the operation by the MURC method, it is necessary to consider the iron oxide production conditions of the top blowing condition and the bottom blowing condition.
Therefore, the present inventors have conducted extensive studies and investigated the correlation between the bottom-blowing agitation power density and the energy density due to iron oxide formation determined by the top-blowing conditions. As a result, a linear correlation could be confirmed. Furthermore, it was possible to establish a correlation under the condition that the slopping index and the middle waste rate deteriorated.

(supplement)
In many converters, refining is carried out under the condition of a large amount of gas injection from multiple tuyeres from the bottom of the furnace, and the bottom-blowing agitation power is sufficiently high. Therefore, it is presumed that in the prior art, the stirring conditions for the weakly stirring converter were not assumed. On the other hand, regarding the weakly agitated converter with soft blow lance, attention is focused on the condition of bottom blowing weak agitation that can ensure the intermediate slag rate because the recognition of the problem of securing the intermediate slag rate is extremely low. I didn't.

(Specific description of one embodiment of the present invention)
Hereinafter, a method for refining molten iron according to an embodiment of the present invention will be specifically described.

FIG. 1 is a diagram showing a hot metal refining method according to an embodiment of the present invention.
As shown in FIG. 1, the method for refining molten iron according to one embodiment of the present invention includes a first step of charging molten iron and scrap as main raw materials into a converter 10, top-blowing and A second step of blowing in oxygen by bottom blowing to remove one or more of Si, P, and S from the hot metal 12, and a third step of discharging the slag 14 generated in the converter 10. and a fourth step of blowing oxygen into the converter 10 by top blowing and bottom blowing to deP and deC the hot metal 12 .

“Top blowing” means blowing oxygen downward into the converter 10 from the throat of the converter 10 by a top blowing lance 16 inserted into the converter 10 .
“Bottom blowing” means blowing oxygen upward into the converter 10 with a bottom blowing lance 18 provided at the bottom of the converter 10 .

The weight percent concentration of Si in the main raw material charged in the first step is 0.20 or more and 0.80 or less.
The temperature of the hot metal at the end of blowing in the second step is 1200°C or higher and 1450°C or lower.
The weight percent concentration of C in the hot metal at the end of blowing in the second step is 3.00% or more.
The weight ratio of CaO and _SiO2 in the slag discharged in the third step is 0.6 or more and 2.5 or less.

The second step, which is hot metal pretreatment, is performed so as to satisfy the following formula (1).
3.60≦g×Q _t ′/S−0.60×ε _b ≦4.90 (1)
however,
g is the gravitational acceleration [m/s ² ];
Q _t ' is the surplus oxygen amount [kNm ³ /hr] that does not contribute to decarbonization in top blowing;
S is the surface area of the hot metal (volume inside the converter/height inside the converter) [m ² ],
ε _b is the bottom-blowing agitation power density [kW/t].

FIG. 2 is a vertical cross-sectional view of a furnace body of a converter for carrying out the method for refining molten iron according to one embodiment of the present invention.
The “volume inside the converter” is the volume of the internal space 22 (dotted portion) of the furnace body 20 in the state where the bricks are stacked inside the furnace body 20 of the converter 10 .
The “height in the converter” is the distance (height) H from the bottom 24 of the furnace body 20 to the throat 26 when bricks are stacked in the furnace body 20 .
The "bottom-blown agitation power density" is the energy density contributing to the agitation given per 1 ton of hot metal calculated from the blowing energy of the bottom-blown gas of the converter.

The surplus oxygen amount Q _t ′ [kNm ³ /hr] in Equation (1) is obtained by Equation (2) below.
Q _t '=(1−η)×Q _t (2)
however,
η is the top-blowing decarburization efficiency [-],
_Qt is the top-blowing oxygen feed rate [kNm ³ /hr].

The top-blown decarburization efficiency η in the equation (2) is obtained by the following equation (3).
η=0.98−40.67/ε _t (3)
However, ε _t is the top-blowing stirring power density [kW/t].
The "top-blown agitation power density" is the energy density contributing to the agitation given per 1 ton of hot metal calculated from the dynamic pressure energy of the top-blown gas in the converter.
The decarburization oxygen efficiency η is the theoretical amount/actual amount ratio of the amount of oxygen used for combustion of hot metal components, empirically obtained from blow temper test results.

ただし、
ｄは、上吹きランスのノズル孔のスロート径［ｍ］、
ｕ_０は、上吹きランスのノズル孔の出口から噴出されるガスの線流速［ｍ／ｓ］、
θは、ノズル孔の中心軸に対するガスの放射方向への広がり角度［ｄｅｇ］、
Ｗ_Ｍは、転炉で精錬される溶銑の重量［ｔ］、
Ｘは、溶銑浴面に対する上吹きランスの高さ［ｍ］である。 FIG. 3 is a graph showing the relationship between decarburization oxygen efficiency η and reciprocal 1/ε _t of top-blown stirring power density.
According to Kato et al., the top-blown stirring power density ε _t in Equation (3) is obtained by the following Equation (4) (Y. Kato et al.: Tetsu-to-hagane, 76 (1990), p.560 ).

however,
d is the throat diameter [m] of the nozzle hole of the top blowing lance;
u ₀ is the linear flow velocity of the gas ejected from the outlet of the nozzle hole of the top blowing lance [m/s];
θ is the spread angle [deg] of the gas in the radial direction with respect to the central axis of the nozzle hole;
_WM is the weight of molten iron refined in the converter [t],
X is the height [m] of the top blowing lance with respect to the hot metal bath surface.

FIG. 4 is a vertical cross-sectional view of a converter for carrying out a method for refining molten iron according to an embodiment of the present invention.
FIG. 4 shows the height X of the top blowing lance 16 with respect to the bath surface 12A of the hot metal 12 as an example of "the height of the top blowing lance with respect to the hot metal bath surface".

FIG. 5 is an enlarged vertical cross-sectional view of the main portion of the tip side portion of the top blowing lance.
The nozzle hole 30 is formed in a tapered shape expanding in diameter from a throat 30A (entrance) to an outlet 30B.
FIG. 5 shows the diameter d of the throat 30A (minimum diameter portion of the nozzle hole 30) as an example of the "throat diameter of the nozzle hole of the top-blowing lance".
Further, the linear flow velocity _u0 of the gas 32 ejected from the outlet 30B of the nozzle hole 30 is shown as an example of "the linear velocity of the gas ejected from the outlet of the nozzle hole of the top blowing lance".
Also, as an example of the "angle of spread of the gas in the radial direction with respect to the central axis of the nozzle hole", the angle of spread of the gas 32 in the radial direction with respect to the central axis 34 of the nozzle hole 30 is shown.

ただし、
γは、比熱比［－］、
Ｒは、気体定数［Ｊ／（Ｋ・ｍｏｌ）］、
Ｔ_１は、ノズル孔から噴射される前のガスの温度［Ｋ］、
Ｐ_ａｔｍは、大気圧力［Ｐａ］、
Ｐ_１は、ノズル孔から噴射される前のガスの圧力［Ｐａ］、
Ｍは、酸素ガスのモル重量［ｋｇ／ｋｍｏｌ］である。 Considering the expansion of the gas before and after being injected from the nozzle hole of the top-blowing lance, the linear flow velocity u ₀ of the gas in Equation (4) is obtained by Equation (5) below.

however,
γ is the specific heat ratio [-],
R is the gas constant [J / (K mol)],
_T1 is the temperature [K] of the gas before it is injected from the nozzle hole;
Pat _atm is the atmospheric pressure [Pa];
P ₁ is the pressure of the gas before it is injected from the nozzle hole [Pa],
M is the molar weight of oxygen gas [kg/kmol].

According to Mori and Sano et al., the bottom-blown agitation power density ε _b is obtained by the following formula (6) (K.Mori, M.Sano: Tetsu-to-hagane, 67 (1981), p.672).
ε _b =22.26×Q _h ×T _M ×LN(1−9.8×ρ _M ×h/P _atm )/W _M (6)
however,
Q _h is the supply rate of the bottom-blown gas [Nm ³ /hr];
_TM is the temperature of molten iron during refining in a converter [K],
ρ _M is the density of hot metal [kg/m ³ ],
h is the depth of hot metal [m].

According to the hot metal refining method according to the embodiment of the present invention, slopping can be avoided in hot metal pretreatment by adjusting the amount of surplus oxygen within an appropriate range. In addition, by appropriately adjusting the bottom-blowing agitation energy in the intermediate waste, an appropriate intermediate waste rate can be ensured.

The results of experiments applied to actual equipment are shown below.
Evaluation of slopping and intermediate slag during blowing was carried out in the following manner.
"Slopping" is leakage of slag and bare metal out of the converter.
The slopping was evaluated by the slopping rate [%], which is the weight ratio of [weight of waste discharged from furnace] to [total weight of furnace contents], as shown in the following equation (7). Then, the conditions under which the slopping rate was 2.0% or less were regarded as acceptable.
Slopping rate [%]=[weight of under-furnace discharge]/[total weight of furnace contents]×100 (7)
The "underfurnace discharge weight" is the weight of slag and ingot discharged from the converter during blowing.
"Furnace input total weight" means the weight of hot metal and scrap charged into the converter.

In addition, as shown in the following formula (8), the intermediate slag rate is calculated by calculating the ratio of CaO and SiO ₂ charged into the converter from the components of the slag collected at the end of blowing in the converter. sought. Then, the conditions under which the intermediate waste rate was 60% or more were regarded as acceptable.
Intermediate slag rate [%]={(C/S)×[SiO ₂ ] ₄ −[CaO] ₄ )/([CaO] ₂ −(C/S)×[SiO ₂ ] ₂ } (8 )
however,
(C/S) is the weight ratio of CaO and _SiO2 components in the slag collected after the fourth step,
[CaO] _i is the CaO equivalent introduced in the i step,
[SiO ₂ ] _i is the equivalent of SiO ₂ charged and produced in the i-th step.

FIG. 6 is a graph showing the results of this experiment.
In FIG. 6, the vertical axis indicates the forming index [W/t×10 ⁴ ], and the horizontal axis indicates the bottom-blowing stirring power density [kW/t].
The forming index [W/t×10 ⁴ ] is defined under top-blowing conditions, is the energy density in the rising direction of the slag accompanying the volume increase, and is defined by the following formula (9).
Forming index [W/t×10 ⁴ ]=g×Q _t ′/S (9)
however,
g is the gravitational acceleration [m/s ² ];
Q _t ' is the surplus oxygen amount [kNm ³ /hr] that does not contribute to decarbonization in top blowing;
S is the surface area of the hot metal (volume in the converter/height in the converter) [m ² ].

Table 1 is a list showing the conditions and results of this experiment.

Table 1 shows the results of experiments using an actual converter. "Invention Examples 1 to 6" satisfy the condition of formula (1), and "Comparative Examples 1 to 6" do not satisfy the condition of formula (1).
Under conditions in which both the slopping rate and the intermediate slag rate are acceptable, a linear optimum range of the foaming index and the bottom-blowing agitation power density is obtained. The slope when linearly approximating the linear optimum region of this forming index and the bottom blowing agitation power density is 0.60, and when the intercept at the bottom blowing agitation power density of 0 is evaluated, the blowing condition that was judged to be acceptable is exists within a certain range (i.e., 3.60 or more and 4.90 or less) as defined by formula (1), and the condition for failing the evaluation is outside the range defined by formula (1) existed in
Therefore, it can be said that, as in "Invention Examples 1 to 6", if the condition of formula (1) is satisfied, an appropriate amount of intermediate waste can be ensured while avoiding slopping in hot metal pretreatment.

An embodiment of the present invention has been described above, but the present invention is not limited to the above, and can of course be implemented in various modifications without departing from the gist of the present invention. is.

10 converter 12 hot metal 14 slag 16 top blowing lance 18 bottom blowing lance 20 furnace body 30 nozzle hole

Claims (1)

A first step of charging molten iron and scrap as main raw materials into a converter;
a second step of blowing oxygen into the converter by top-blowing and bottom-blowing to decarburize the hot metal and to remove one or more of Si, P, and S from the hot metal;
a third step of discharging the slag generated in the converter;
a fourth step of blowing oxygen into the converter by top blowing and bottom blowing to deP and deC the molten iron;
The weight percent concentration of Si in the main raw material charged in the first step is 0.20 or more and 0.80 or less,
The temperature of the hot metal at the end of blowing in the second step is 1200 ° C. or higher and 1450 ° C. or lower,
The weight percent concentration of C in the hot metal at the end of blowing in the second step is 3.00% or more,
The weight ratio of CaO and _SiO2 in the slag discharged in the third step is 0.6 or more and 2.5 or less,
The second step is performed so as to satisfy the following formula (1),
Method of refining hot metal.
3.60≦g×Q _t ′/S−0.60×ε _b ≦4.90 (1)
however,
g is the gravitational acceleration [m/s ² ];
Q _t ' is the surplus oxygen amount [kNm ³ /hr] that does not contribute to decarbonization in top blowing;
S is the surface area of the hot metal (volume inside the converter/height inside the converter) [m ² ],
ε _b is the bottom-blowing agitation power density [kW/t].

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