JPH079022B2 - Method of dephosphorization and desulfurization of hot metal - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a method of performing dephosphorization and desulfurization of hot metal together with desiliconization which proceeds at the same time.

[Conventional technology]

When CaO-based flux is used, Si, P and S in the hot metal are removed according to the equations (1), (2) and (3), respectively.

Si + 20 → SiO ₂ (1) 3CaO ＋ 2P ＋ 50 ＝ 3CaO ・ P ₂ O ₅ (2) CaO + S ＝ CaS + O (3) When CaO is supplied together with O ₂ to the hot metal containing Si, in addition to the above reaction, (4) Formula CaO + Si + 20 → CaO ・ SiO ₂ Because the reaction of (4) occurs simultaneously, the progress of the dephosphorization and desulfurization reactions is greatly hindered. On the other hand, the desulfurization reaction is a reduction reaction, while the desiliconization and dephosphorization reaction is an oxidation reaction.

Therefore, in order to carry out dephosphorization and desulfurization under more suitable conditions, dephosphorization and desulfurization have been devised in two or more stages such as desiliconization or dephosphorization and desulfurization. For example, the most general method is to perform desiliconization treatment in advance to reduce the [Si] concentration, remove the slag once, and perform simultaneous dephosphorization and desulfurization treatment in the same or different cases or in a reaction vessel.

Further, in recent years, since the heat loss in the hot metal pretreatment process lowers the thermal tolerance of the converter, attempts to use the top blowing of gaseous oxygen together for the purpose of heat compensation in the pretreatment are popular. However, in this case, the simultaneous desulfurization rate is remarkably reduced, and additional desulfurization treatment is inevitable as the third stage. It is said that the reason is that the oxygen potential of the top slag, which is presumed to be where desulfurization reaction occurs, increases.

Also, when performing desulfurization and desulfurization separately, that is, when performing desulfurization treatment in advance before desiliconization / desulfurization, or when performing additional desulfurization treatment as described above, different types of flux for desulfurization and desulfurization are used. It is common to do. For example, CaO-based flux containing iron oxide is used for dephosphorization, whereas CaO-CaCO ₃ system containing no iron oxide, C
Fluxes such as aC ₂ or soda ash (Na ₂ CO ₃ ) series are often used.

As described above, separation of desiliconization, dephosphorization and desulfurization reactions and optimization of reaction conditions have been achieved by changing the treatment location and the type of refining agent (flux) and increasing the number of treatments. The purpose of separation / optimization of each reaction is to improve the efficiency of each reaction and eliminate the required basic unit of refining agent (flux) as much as possible.

However, on the other hand, such division of the process and multi-stepping will cause a basic problem. That is, if the treatment place and the number of treatments increase, not only the treatment time and the temperature decrease in all the processes increase, but also the operating cost such as the refractory basic unit increases. Further, as the types of flux used increase, incidental equipment or maintenance costs thereof increase.

Therefore, if desiliconization, dephosphorization, and desulfurization are efficiently carried out with a single flux in a single vessel, it will be of great significance from the viewpoint of greatly reducing operating costs. However, there is still an example of an attempt to desiliconize, dephosphorize, and desulfurize high-Si hot metal in a single treatment up to the product standard value level of ordinary steel, and to propose an effective method for increasing the treatment efficiency in that case. I don't see.

[Problems to be solved by the invention]

INDUSTRIAL APPLICABILITY The present invention enables desiliconization, dephosphorization and desulfurization of high Si hot metal even in a single batch process in a single container, and only one type of flux is required. It is intended to provide a method capable of reducing

[Structure of Invention]

The present invention is a CaO-based refining agent (flux) containing solid compound oxygen for the total amount of gaseous oxygen in order to perform dephosphorization and desulfurization of high Si hot metal having a Si concentration of 0.20% or more in a single vessel.
With the method of injecting into hot metal with
Keep the CaO / ΣO ₂ ratio low in the first half of the injection (CaO / ΣO ₂ = 1.
5 to 2.0) After prioritizing desiliconization and dephosphorization, the operation of changing the ratio of the flux blowing rate and the gaseous oxygen flow rate was performed only once, and the CaO / ΣO ₂ ratio was changed to the value of the first half in the latter half of the blowing. Provided is a method for desiliconization, dephosphorization, and desulfurization of high-Si hot metal, which is characterized by accelerating desulfurization and mainly desulfurization by increasing the content by more than twice.

[Specific disclosure of invention]

 First, the terms are defined.

Gaseous oxygen ratio α However, W _F = flux amount (kg) O ₂ * = oxygen ratio in the flux (Nm ³ / kg) ΣO ₂ = total oxygen amount (Nm ³ ) calcium oxide / total oxygen ratio CaO * = Weight ratio of CaO in the flux. The inventors of the present invention used CaO-CaF ₂ -iron oxide (scale) (5) with a highly oxygen-enriched carrier gas having a gas oxygen concentration of 80 to 95 vol.
0: 10: 4) We conducted several experiments on injection of system flux into high Si hot metal with [% Si] ≧ 0.20, and found the following facts.

That is, when various CaO / ΣO ₂ ratios were blown, the results shown in FIG. 1 were obtained for the material unit required for dephosphorization, as disclosed in the prior application (Japanese Patent Application No. 62-93375). First
The figure shows 85% when [% Si] of hot metal before treatment is 0.20 to 0.40.
The unit of CaO and the unit of total oxygen required to achieve the dephosphorization rate of 0.100% → 0.015% are shown.

That is, keeping CaO / ΣO ₂ within the range of 1.5 to 2.0
First, we found that the dephosphorization efficiency is the best, that is, the material unit consumption of CaO, ΣO _2, etc. can be minimized.
In the dephosphorization reaction shown in the formula, in the range where the CaO / ΣO ₂ ratio is high (CaO / ΣO ₂ ≧ 2.0), CaO is excessive, so it is possible to reduce the CaO basic unit while the ΣO ₂ basic unit remains almost constant. Yes, but C
If the aO / ΣO ₂ ratio is excessively decreased (CaO / ΣO ₂ ≦ 1.5), CaO
It is considered that the dephosphorization efficiency for ΣO ₂ is reduced even if ΣO ₂ is increased due to the shortage of oxygen.

However, before treatment [% Si] = 0.35 to 0.40, CaO / ΣO ₂
In the range of 1.5 to 2.0, there was a problem that the simultaneous desulfurization rate at the time when 85% of the phosphorus removal rate was obtained was as low as 15 to 30%.

Then, the inventors of the present invention tried an experiment for the purpose of promoting desulfurization under the condition of higher CaO / ΣO ₂ using a flux having a higher CaO concentration, and as shown in FIG. If the CaO / ΣO ₂ ratio is increased when the [% Si] _I is the same, the desulfurization rate per unit of CaO (before treatment [% S] = 0.025
~ 0.030) increased. We have
Especially in Fig. 2, CaO / ΣO ₂ = 2.0, CaO = 30kg / THM
The desulfurization rate at (ΣO ₂ = 15 Nm ³ / THM) is at most 40%, while at CaO / ΣO ₂ = 4.0 CaO = 30 kg / THM (ΣO ₂ = 7.5 Nm ³ / THM) Attention was paid to the fact that a desulfurization rate of 70% was obtained. In both cases, more than 7.5 Nm ³ / THM of ΣO ₂ is supplied when CaO = 30 kg / THM is blown in, and the desiliconization reaction, which precedes dephosphorization, has already ended (△ [% Si] = 0.35-
0.40), so the amount of CaO spent in Eq. (4) is also the same. Nevertheless, the large difference in the desulfurization rate suggests that the desulfurization reaction represented by the equation (3) has a large effect of lowering the oxygen potential. That is,
Desulfurization did not proceed slowly when the CaO intensity was increased while the CaO / ΣO ₂ ratio was low, and it was revealed that increasing the CaO / ΣO ₂ ratio is an essential condition for promoting desulfurization.

Therefore, enough ΣO ₂ is necessary to obtain the desired dephosphorization rate.
If the basic unit is secured and the CaO basic unit is increased (CaO / ΣO ₂
It is possible to accelerate desulfurization at the same time as desiliconization and phosphorus removal.

Therefore, the present inventors for the purpose of further improving the efficiency by further reducing the increase in the CaO unit consumption required for simultaneous desulfurization,
The present invention has been devised based on the above findings. The method is that the CaO / ΣO ₂ ratio is 1.5 to 2.0 (kg / Nm ³ ) in the first half of injection.
The ratio α is lowered after the silicon removal and phosphorus removal are preferentially promoted while keeping the temperature within the range of, that is, the ratio of the blowing velocity W _F (kg / min) and the gas oxygen flow rate Q _o2 (Nm ³ / min). By increasing CaO /
This is a method characterized by increasing ΣO ₂ more than twice that in the first half and promoting desulfurization. The reason for limiting the first half CaO / NA: 0.75, o ₂ ratio to accelerate the desiliconization and dephosphorization in the range of 1.5 to 2.0, as shown in FIG. 1, CaO and NA: 0.75, o ₂ required this range the desiliconization-dephosphorization This is because both the basic units can be minimized without excess or deficiency. Further, the operation of increasing the CaO / ΣO ₂ ratio, that is, increasing W _F / Q _o2 should be performed at a low Si concentration of [% Si] of 0.10 to 0.15% or less.
This is because the supply of O ₂ is dominant in the promotion of desiliconization as shown in equation (1), and CaO basically does not contribute to the promotion of desiliconization. That is, even if CaO / ΣO ₂ is increased from a high Si concentration range where [% Si] is 0.10 to 0.15% or more, CaO is excessively blown. The reason why the CaO / ΣO ₂ value in the latter half is more than twice that in the first half is to increase the difference between CaO / ΣO _{2 in} the first half and the latter half and clarify the optimal split effect in both periods.

FIG. 3 (a) shows W _F (kg / min) and Q _o2 (Nm in the method of the present invention.
³ / min), and FIG. 3 (b) shows the behavior of Si, P and S at that time. W immediately after 8 minutes
_{Although F} (kg / min) was increased, Q _o2 (Nm ³ / min) was decreased and CaO / ΣO ₂ was increased, desulfurization has been significantly promoted since the change. FIG. 4 shows the relationship between the desulfurization amount per unit CaO unit of 10 kg / t and CaO / ΣO _2. The X and the marks in the figure show the results of the method of the present invention. It is divided into the first half and the latter half of each injection, and is plotted against the average value of CaO / ΣO ₂ in each period. Even after changing α (changing the W _F / Q _o2 ratio), a desulfurization efficiency equal to or higher than that at the time of constant α injection when a flux with a high CaO concentration was used was obtained. W _F / Q _o2 ratio during the change operation only, CaO / ΣO
_The desulfurization efficiency (for CaO) can be easily improved by increasing the ₂ ratio. However, as can be seen from Fig. 1, CaO /
Increase of NA: 0.75, o ₂ is preferred to promote dephosphorization so improve the efficiency of NA: 0.75, o ₂ for dephosphorization.

Fig. 5 is a plot of CaO unit required to obtain a simultaneous desulfurization rate of 60% when the dephosphorization rate is 85% or more, against CaO / ΣO ₂ . In the case of the method of the present invention, total CaO (kg / t) and ΣO ₂ (kg / t)
It is plotted against the ratio of t). As can be seen from the comparison when the CaO / ΣO ₂ ratios are equal, the method of the present invention can further reduce the CaO unit consumption compared to the case of constant α injection. This is the dephosphorization with desiliconization the period of low CaO / NA: 0.75, o _2, and mainly desulfurization with dephosphorization high periods of CaO / NA: 0.75, o _2, because they can be efficiently processed in the minimum amount of CaO, respectively . That is, the present inventors
They have found that the dephosphorization and the dephosphorization / desulfurization can be carried out separately under more preferable conditions by only changing the ratio of W _F and Q _{o2 during} the blowing.

By the way, the phenomenon that changing the ratio of W _F (kg / min) and Q _o2 (Nm ³ / min) in the middle of dividing silicon dioxide / dephosphorization and desulfurization with high efficiency preferentially is gas O ₂ (gas This was remarkable in the method of enriching the entire amount of acid) in the flux carrier gas. The inventors made an attempt to blow 50% of the supplied O _{2 under} the same conditions such that the CaO / ΣO ₂ ratio before and after blowing, the increase of W _F , and the decrease of Q _o2 are all equal. As shown by the triangle mark in FIG. 4, the improvement in desulfurization efficiency with the increase in the CaO / ΣO ₂ ratio was small. This is thought to be because the oxygen potential of the top slag is kept high in the case of O ₂ top blowing, which is not preferable for desulfurization.

〔Example〕

Examples according to the present invention will be described below. All experiments were conducted in a 5 ton bottom blowing furnace. The bottom blowing nozzle is a single tube nozzle made by boring alumina fired bricks by boring, and has an inner diameter of 5 mm and six nozzles. The blowing of the flux was performed by a differential pressure control type powder feeder. Flux blow rate is 10-32 kg / min, gas O ₂ blow rate is 0.5
~ 3.0Nm ₃ / min N ₂ blowing speed for flux transfer is 0.18
It was Nm ³ / min, and the O ₂ concentration in the carrier gas was 70 to 95%. The pre-treatment component of the hot metal is [% C] = 4.3 to 4.6, [% Si]
= 0.20 to 0.45, [% P] = 0.095 to 0.105, [% S] = 0.
The temperature is 025 to 0.030, and the pretreatment temperature is 1,280 to 1,420 ° C. The composition of the flux is _{50% CaO-10% CaF 2} -40% scale, in the flux 100kg Includes O ₂ of 6 Nm ^3, blowing time is 10 to 20 minutes.

Table 1 shows the blowing conditions, material consumption rate, dephosphorization rate / desulfurization rate, and temperature change during treatment in the method of the present invention and the comparative method. Table 1 shows all [% Si] _I = 0.36 to 0.4
An example in the case of 0 is shown. In a single batch treatment, dephosphorization and desulfurization were carried out aiming at a level equal to or higher than the product specifications for P and S for ordinary steel such as low carbon aluminum killed steel. ([% P] _f = 0.015 to 20 (Phosphorus removal rate 85%) [%
S] _f = 0.010 to 0.014 (desulfurization rate 60%)) Since desiliconization proceeds prior to dephosphorization, of course [% Si] after treatment is tr (≤
0.001).

In Comparative Example 4, CaO / ΣO ₂ was blown with 1.8 kept almost constant. The simultaneous desulfurization rate at a dephosphorization rate of 85% is at most 22%,
Furthermore, even if CaO was increased to 24 kg / t, the desulfurization rate remained at 33%. In this experiment, the decarburization amount △ [% C] is ΣO ₂
= 10 Nm ³ / t, about 0.5% when the pre-treatment [% Si] is 0.36 to 0.40, and when the blow-off of Comparative Example 4 is stopped, Δ
[% C] reached about 1.0%. CaO / ΣO ₂ remains low CaO
Even if the amount is increased, the stagnation of desulfurization unnecessarily promotes decarburization.

The average values of CaO / ΣO ₂ of the present invention methods 1, ₂ , and 3 are substantially equal to those of Comparative Examples 1, 2, and 3, respectively. Inventive method 1, 2,
In 3, both in the course of blow W _F a (kg / min) 2-3
Times are kept at Q _o2 (Nm ³ / min) 1 / 5-2 / 3 2 times or more of the first half of that decrease Well the second half of CaO / ΣO ₂ up along with the increase to. The Comparative Example 5 but was changed W _F / Q _o2 ratio in the course of blowing, a comparative example in which CaO / NA: 0.75, o ₂ ratio of the second half is less than twice that of the first half.

In the present invention method 1 and the comparative example 1, CaO = 20 kg / t, ΣO ₂ = 8 Nm ³
The desulfurization rate of the method of the present invention is 10% higher than that of / t. In the present invention method 2 and the comparative example 2, when CaO = 26 kg / t and ΣO ₂ = 8 Nm ³ / t, the desulfurization rate is 16% higher and the dephosphorization rate of 85% or more can be secured by the method of the present invention. In order to obtain the simultaneous desulfurization rate of 60%, the method of the present invention can reduce CaO = 6 kg / t and ΣO ₂ = 2.1 Nm ³ / t.
Further, in the method 3 of the present invention and the comparative example 3, the simultaneous desulfurization rate is about
In order to reach the extremely low sulfur concentration range of 75% or more ([% S] ≦ 0.007), the method of the present invention can reduce CaO = 10 kg / t and ΣO ₂ = 2.2 Nm ³ / t. Further, in Comparative Example 5, the average value of CaO / ΣO ₂ values is almost the same as that of the method 1 of the present invention and Comparative Example 1, but Ca
The desulfurization rate when the O basic unit is about 21 kg / t is 1 compared with the method 1 of the present invention.
It was 1% lower and almost equal to Comparative Example 1. This is the latter half of CaO /
This is because ΣO ₂ was less than twice that in the first half, and the degree of acceleration of desulfurization in the second half was also suppressed. Ca in the second half
If the O / ΣO ₂ ratio is drastically increased and kept at twice or more of the CaO / ΣO ₂ ratio in the first half of the period, the reaction period of both reactions will be sufficiently divided and optimized, and the unit dose of the drug can be minimized.

Unless there is a special requirement for melting ultra-low phosphorus or ultra-low sulfur steel, it is necessary to reach the target level in a well-balanced manner without causing excess quality in only one of [% P] and [% S]. Desulfurization becomes difficult because of the aim of reducing the CaO unit as much as possible, and in the simultaneous desiliconization, dephosphorization, and desulfurization simultaneous treatments, the method of the present invention is effective in intensively promoting desulfurization, resulting in excessive desulfurization. There is a merit that it can also reduce the ΣO ₂ intensity per minute.

[Effects of the Invention] As described above, according to the method of the present invention, desiliconization of high Si hot metal,
Split and optimize dephosphorization and desulfurization in a single vessel
It is possible to use only one type of flux in one batch process, and the CaO and ΣO ₂ basic units required for desiliconization and dephosphorization / desulfurization can be reduced as much as possible.

[Brief description of drawings]

Figure 1 shows that the [% Si] of the hot metal before treatment was 0.20 to 0.25 and 0.
In the case of 35 to 0/40, the total O ₂ (Σ
O ₂₎ shows the intensity and CaO intensity relative to _{CaO / ΣO 2 (kg / Nm} 3). FIG. 2 is a diagram showing the desulfurization rate when CaO of 10, 20, 30 kg / t is used, with respect to CaO / ΣO ₂ (kg / Nm ³ ). Third
Figure (a) shows the flux blowing velocity W _{F in the} method of the present invention.
The figure which shows an example of the time-dependent change of (kg / min) and gaseous oxygen flow rate. Fig. 3 (b) shows [% Si] when 50% CaO-10% CaF ₂ and -40% scale flux were used to blow 5ton of hot metal at a blowing speed according to Fig. 3 (a). , [% P],
The figure which shows the time-dependent change of [% S]. FIG. 4 is a diagram showing the desulfurization amount Δ [% S] per CaO = 10 kg / t with respect to CaO / ΣO ₂ (kg / Nm ³ ). Fig. 5 shows the simultaneous desulfurization rate of 60 when the dephosphorization rate is 85% or more.
The figure which shows the CaO basic unit required to obtain% with respect to CaO / ΣO ₂ (kg / Nm ³ ).

Claims (3)

[Claims] 1. In order to perform dephosphorization and desulfurization of hot metal having a Si weight concentration of 0.20% or more in a single vessel, the entire amount of gaseous oxygen is injected into the hot metal together with a CaO-based refining agent (flux) containing solid compound oxygen. a method of, after advancing the first half CaO / NA: 0.75, o ₂ ratio lower maintained by desiliconization and dephosphorization blow preferentially, mainly with dephosphorization by increasing the CaO / NA: 0.75, o ₂ ratio in the second half of the blow A method for dephosphorizing and desulfurizing hot metal, characterized by accelerating desulfurization. 2. The division of desiliconization / dephosphorization and dephosphorization / desulfurization by changing the CaO / ΣO ₂ ratio is performed by changing the gas oxygen use ratio, that is, the flux blowing rate W _F (kg / min) and the gas oxygen. The method according to claim 1, which is achieved by performing the operation of changing the ratio of the flow rate Q _o2 (Nm ³ / min) once. 3. The CaO / ΣO ₂ ratio during the first half of the operation until the [wt% Si] in the hot metal becomes 0.10 to 0.15% or less is 1.5 to 2.0.
3. The method according to claim 1 or 2, wherein the CaO / ΣO ₂ ratio in the latter half period is kept at twice or more that in the first half period.