JPS58224105A - Preliminary treatment of molten iron - Google Patents

Abstract

PURPOSE:To reduce the cost for a preliminary treatment of molten iron and to improve working efficiency by calculating and controlling the required amts. and compsns. of a refining flux and a gaseous carrier from the actually measured values and target values of the components and temp. of the molten iron before and after the preliminary treatment. CONSTITUTION:The components and temp. of molten iron are compared with the target components and temp. of a preliminary treatment, and the min. amt. of a quicklime refining flux as well as the compsn. and amt. of a gaseous carrier required for achieving said target are calculated. An injection operation is carried out in accordance with the results thereof to reduce the unit of the refining flux in the preliminary treatment of the molten iron, whereby the cost is reduced and the working efficiency is improved. The above-mentioned refining flux consists of a slag forming agent consisting essentially of quicklime, a fluxing agent of >=1 kind among fluorite, rock crystal and colemanite and a solid oxygen source to be mixed according to need. The gaseous carrier consists of >=1 kind among gaseous oxgen or an oxidative gas contg. the same as a component element, gaseous nitrogen and other inert gases.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for pre-treatment of hot metal, and particularly aims to effectively reduce the unit consumption of refining flux used in the treatment.

As is well known, silicon and phosphorus in hot metal can be reduced by reacting with oxygen during a refining process such as converter blowing.

However, when the content of silicon and phosphorus in the treated hot metal is high, in order to remove phosphorus, it is necessary to
Since it is necessary to increase (OaO/si, o, ) and the amount of slag, a particularly large amount of slag expelling agent, such as quicklime, is required, which lengthens the refining time and lowers the temperature of the hot metal. Since the dephosphorization efficiency is poor in a high-temperature atmosphere such as in a furnace, a significant dephosphorization effect cannot be expected.

In addition, removal cannot be expected in converter blowing carried out in an oxidizing atmosphere in the molten pig iron.

For this reason, at present, before the hot metal tapped from the blast furnace is charged into the converter for oxidation refining, impurity phosphorus is removed by injecting it into the hot metal bath together with 7 lux of carrier gas. A so-called preliminary treatment of hot metal is carried out to remove slag and other substances. In this way, the amount of auxiliary raw materials used for dephosphorization (hereinafter referred to as deP) and desulfurization (same desulfurization) in the converter steel manufacturing process is reduced, making it easier to melt and manufacture low-phosphorus and low-sulfur steel. At the same time, the yield of iron can be improved by reducing the amount of slag produced.

By the way, although there have been various studies on the composition of the refined flux used in such pretreatment, they have all focused on reaction efficiency and have not been studied from a cost perspective. There are very few cases.

Moreover, this type of refining furnace ξnox is usually used with each component mixed in advance, and it has not been possible to adjust the blending ratio according to the components and temperature of the hot metal. For this reason, in each component of refined flux,
In particular, hazardous components such as quicklime and fluorite were mixed into the mixture somewhat in order to ensure safety, and the amount was much higher than the amount needed to make them the target components after preliminary treatment.

The addition of gold to the slag agent causes an unnecessary increase in the amount of slag produced, which not only increases the smelting flux consumption rate but also reduces the efficiency of pretreatment operations, so improvement is desired. Ta.

This invention was developed in view of the above circumstances, and uses inexpensive quicklime as a slag-forming agent, and also minimizes the amount of each component of the smelting flux, including it, to reduce the amount of smelting flux to 7 lacs. By reducing the basic unit, it is possible to reduce the cost in pre-treatment of hot metal while improving work efficiency.

In other words, this invention provides a method for pre-treating hot metal by injecting quicklime-based refined 7 lac into a hot metal bath using a carrier gas. By comparing the composition and temperature of the hot metal of Airiken, we calculate the minimum amount of components of the refining flux and the composition and amount of carrier gas necessary to achieve the target, and then start the injection operation based on the calculation results. By doing so, we aim to solve the above problem.

The refined 7 lacs used in this invention include a slag agent mainly composed of quicklime, a solvent such as clapstone, cryolite, and colemanite, and a solid oxygen source mixed as necessary, such as iron ore and mill scale. Formulations of are advantageously suited.

Further, as the carrier gas, a gas consisting of one or more selected from oxygen or an oxidizing gas containing oxygen as a component, nitrogen gas, and other active gases is advantageously suitable.

This invention will be specifically explained below based on the experimental results that led to this invention.

Figures 1a and b show the dephosphorization rate and the amount of oxygen supplied that contributes to dephosphorization when preliminary treatment is performed using quicklime as a slag-forming agent and oxygen gas mixed in carrier gas as an oxygen source. and the relationship with the amount of quicklime supplied.

While the dephosphorization rate increases almost linearly in proportion to the amount of oxygen supplied, there is no particularly strong correlation with the amount of lime supplied. In other words, it can be seen that in the dephosphorization of hot metal using quicklime-based refined 7 lux, the dephosphorization reaction depends more strongly on the amount of oxygen than on quicklime.

In addition, Fig. 2 a and b show the P distribution between slag and metal (
(%P,O,)/C%Pal) and S distribution ((%S
)/[%S]) are shown as a function of the ratio of the amount of quicklime supplied to the amount of oxygen supplied.

From FIG. 2a, it can be seen that dephosphorization is almost uniquely determined by the amount of supplied oxygen, and that the amount of quicklime that is sufficient to fix P is sufficient. Furthermore, as shown in the figure, it is well known that the greater the amount of quicklime and the lower the amount of oxygen, the more progress is made in removing S.

In this way, if the amount of supplied oxygen is simply increased, dephosphorization progresses, but
On the other hand, increasing the amount of quicklime supplied will result in de-S
Although progress is made, the amount of quicklime is more than necessary for P removal, which unnecessarily increases the basic unit of refining flux.

Next, we added the relationship between the calculated basicity of the produced slag and the PIS distribution to the results shown in Figs. The results of investigating the relationship between [%P] and [%S] are shown in Part 8.
It is organized and shown in the figure.

The figure shows that there is no need to add a large amount of quicklime as long as the required m
It can be seen that an amount of quicklime corresponding to the target S is required under the amount of oxygen required for dephosphorization as described above. For example, to obtain [%P)-0.02 after pretreatment, 8 N
m'/l of oxygen is required, and the required amount of quicklime in this case is 18 kg/l. -C%8 after 4-way pretreatment]
6′-” which forms −°・°10 means that the amount of oxygen supplied is 6 N.
m'/l, it is necessary to secure 25 kg/l of quicklime. Therefore, the target [%P].

In order to achieve [%S] at the same time, □” per ton of molten steel.
This requires 8 Nm of oxygen and 25 kg of quicklime.

By the way, the oxygen sources used in pretreatment include solid oxygen sources such as iron ore and mill scale, and gaseous oxygen sources such as oxygen gas, and the ratio of their use is determined by the target temperature of the hot metal after pretreatment. . In other words, for example, if all the oxygen required for pretreatment is supplied from a solid oxygen source, the temperature drop of the hot metal will increase and there is a risk that it will fall below the target value. By replacing all with a gaseous oxygen source as appropriate,
The target temperature can be easily achieved.

Next, a description will be given of how to calculate the required amount of each component of the seven lacs of refining and the composition and amount of the carrier gas when deP and S are removed from hot metal according to the method of the present invention.

↑ Each hot metal component before pretreatment [%S soil]. .

[%P]. , [%S]. , the temperature before treatment is T. Also, assume that the target components are represented by [%P)f and [%s)f, and the target temperature is represented by Tf. As is clear from the above-mentioned FIG. 1, the oxygen ml vos required for dephosphorization is (% Si ). and [%P
]. , [%P) can be expressed as a function of f as shown in equation (1) below.

Vo, -f, ((%P)., (:%p)f, (%Si
n. ) -1-(1) Also, the amount of oxygen V. , the cumulative decrease in osmolarity ΔS1 is expressed by the following formula (2), % formula (2). Here, the amount of quicklime W7ine required for dephosphorization is expressed by the following formula (8).

It is found as a solution to the simultaneous equations in (4).

log (%P)/[%”'f −f8 (vos +
Δsx, w, 1m0) ---(s)1000((%P
). −C%P)f)−(%” )×”81&q −
----(4) Here, (%P): P concentration Wslati in the slag after preliminary treatment is the amount of slag after preliminary treatment Ws
zag=f4(ΔSi, W71me) (8) Let A be wji and me obtained by equation (4).

-The amount of quicklime required for force theory S, W/, 1m6, is calculated using the following formula (5)
+ (6).

It is found as the solution of the simultaneous equations.

log ((%S)/[%5)f)-f, (vo,, Δ
S soil + Wlime)--n5) 1ooo (C%Sol.

-C%S:]f)-(%S)xWszag-1---(
61 (%S) + S concentration in slag after pretreatment (5),
If W7ime obtained by equation (6) is B, the target PI
The amount of quicklime that simultaneously satisfies SFfiJ is the greater of A and H.

The amount of oxygen and quicklime required was determined above.

Next, regarding the source of the required amount of oxygen, if the amount of oxygen from the gaseous oxygen source is x1 and the amount of oxygen from the solid oxygen source is y, then x
, y is determined by the following equation ('y) t (s1).

M-f, (Δo, ΔSi, ΔIn, ΔP + W/im
8+ T□+ Tf) ---(7) Vo @ ==x
+ y --- (8) where ΔO= f7 (V
OB+ T□ )Δ" = f8 "'011 '"l
ime +ΔSi, 'I'. )Δp-(%P].-[%
P) f In addition, the slag produced by the pretreatment must have fluidity, and for this purpose it is necessary to mix a substance that lowers the slag melting point, such as fluorite, as a solvent.
As shown in Figure 4, the dephosphorization of quicklime
In order to improve the publicity efficiency, it is desirable that the amount of fluorite be 80 to 50% of the amount of quicklime added.

From the above, the amount of each component of the refining 7 lux and the amount of oxygen gas required to achieve the target P, S and temperature are determined.

The determined amounts of each component are then mixed before pretreatment and blown into the hot metal together with a carrier gas containing the required amount of oxygen gas.

Examples of the present invention will be described below.

・The composition of hot metal before pretreatment is 2m degrees [%Si]. -0,010%, [%P]. = 0.18
0%.

[%s). = o, oao%t To = 185
0℃a ・Target components and temperature after pretreatment [%P]
f≦0, 080%, [%S) f≦0.015%Tf=
1800℃ ([%P). -C%P)f)/[%P). -0,29F
Vo, + 0.411-8ΔS soil [%P]. -C%P]
f = 0.0012 (Wlige” 24.1Δ5i
) (%P) [%S). -C%S:)f-0,0012(
Wlime+24.1Δ51)(%S)T −T =1
．． 4W74z6+5.9W□r6-844Δ5i-18
4ΔOf ΔS soil=o, gz(%5ill. vofAΔc −0,
075(vofA-sΔ5i)Vo, = Vg+ 0
．． 207 Worev9; Amount of gaseous oxygen (Nm/1) Wore "Amount of iron ore (kg/l") The amount of each component and the amount of oxygen gas in the smelting flask obtained by the above calculation formula are as shown in the table. The refining flux having such a mixing ratio was blown into the hot metal charged into the pig iron mixing car using a carrier gas containing the required amount of oxygen gas.

P and 8711 degrees after treatment were as shown in the table.

For comparison, the results are also shown for the sea bream and the surface treatment for P1 and S removal when preliminary treatments were performed according to conventional methods A and H shown below.

Method A iron ore 40% - quicklime 40% - smelting flux having a blending composition of 20% barrel was injected together with a carrier gas having a composition of 20% oxygen - 80% nitrogen at 6 Nm8/min.

Method B iron ore 65% - quicklime 25% - smelting flux having a composition of 10% barrel was blown together with a carrier gas of 20% oxygen - 80% nitrogen at 6 Nm'/min.

As is clear from the surface treatment, when the injection operation was performed according to the method of this invention, the target P and S values were achieved with a smaller amount of refining flux compared to the conventional method, whereas method A In Method B, the basic unit of quicklime is large and S is lowered more than necessary, and in Method B, the basic unit of iron ore is large and P is lowered more than necessary, both of which result in a large temperature drop.

As described above, according to the present invention, in the preliminary treatment of hot metal, the target composition and temperature of the hot metal after the treatment can be adjusted to the minimum necessary M flux, regardless of the composition and temperature of the hot metal before treatment. Since it can be achieved by reducing the amount used, the basic unit of refining flux can be significantly reduced compared to conventional methods.
By reducing costs, it is possible to improve work efficiency in pre-treatment operations.

[Brief explanation of drawings]

Figures 1a and b are graphs showing the amount of oxygen supplied and the influence of quicklime on P removal, and Figures 2a and b are graphs showing the amount of quicklime/oxygen on P and S distribution, respectively. Graph showing v buds, Figure 8 shows [%P] and [%
Figure 4 is a graph showing the relationship between CaO deP consumption efficiency and limestone/quicklime. Figure 1 (a) akfjH element 1-BXr'15i) 0 (Nm3/l) No. 114 (1)) Konajai life quantity -3? , fXC%Sλ]0 (Kf/l) (a) 0 2.0 4,04
Place of residence/
Oxygen amount (K*/Nrn-') Figure 2 (h) Ash amount/- (Amount (Kt/Nm3) Figure 33 Figure 4 shows 7:3 stones Ay = ash

Claims (1)

[Scope of Claims] L When pre-treating the hot metal by injecting a quicklime-based refining flux into the hot metal bath using a carrier gas, the components and temperature of the hot metal before the injection should be adjusted according to the target of the pre-treatment. The minimum amount of refining required to achieve the target is determined by comparing the composition and temperature of the hot metal after treatment.
A hot metal pretreatment method characterized by calculating the component amount of lux and the composition and amount of carrier gas, and performing an injection operation based on the calculation results. 9. Refined flux is mixed with quicklime-based slag agent,
2. A method according to claim 1, which is a formulation of at least one solvent selected from the group consisting of abalite, cryolite and colemanite, and optionally mixed solid oxygen source. & The carrier gas according to claim 1 or 2, wherein the carrier gas is one or more gases selected from oxygen or an oxidizing gas containing oxygen as a component element, nitrogen gas, and other active gases. Method.