JPH0112806B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing low [Si] pig iron that does not require a desilicon treatment (Si in pig iron is hereinafter referred to as [Si]) when supplied to a steelmaking process. It is something.

In the steelmaking process, as is well known, [C]
The heat generated by the oxidation reaction of Si and Si is used as the heat source necessary for refining.

However, when refining with a hot metal content ratio of 70 to 100%, it is sufficient to have 0.30% or less [Si], and theoretically the required amount of heat can be secured with 0.25% or less, and there is no need for more [Si]. It is. In other words, [Si] is generated through a reduction reaction in the ironmaking process, which affects the fuel ratio, and in the steelmaking process, excess [Si] increases the amount of quicklime added, which increases the amount of slag, resulting in increased costs and heat loss. will increase.

If the integrated pig steel process is reviewed from the perspective of energy saving and resource saving, it is possible to reduce [Si] within the allowable range of converter reaction heat.
It becomes necessary to keep it at a low level.

On the other hand, looking at the relationship between the fuel ratio and [Si] in a 5000 m ³ class blast furnace, FR = -4.53 (η _cp ) - 0.08 (BT) + 0.85 (W _H2O ) + 61.74 [Si] + 767.40 N=36 γ=0.99 η _cp (%): Top gas utilization rate BT (°C): Blow temperature W _H2O (g/Nm ³ ): Blow humidity [Si] (%): Si in the pig iron, and this result Even in large blast furnaces exceeding ^5000m3 , the effect coefficients of air temperature, air humidity, and [Si] are as follows.
This value is at the same level as the value conventionally used in small and medium-sized blast furnaces, proving that the reduction of [Si] is also effective from this point of view.

In general, the [Si] in hot metal has a strong correlation with the hot metal temperature as a furnace heat index, and the [Si] level can be controlled by controlling the furnace heat. This may lead to abnormal unloading.

If this condition continues for a long time, it may lead to serious operational troubles.

In other words, low-Si operation at low fuel ratios in blast furnaces, especially large blast furnaces, can only be considered a highly practical technology if Si migration can be suppressed reactively within the furnace while maintaining the heat level in the lower part of the furnace. It's possible.

In general, effective means for achieving low [Si] operation include reducing the total SiO ₂ charged, increasing CaO/SiO ₂ of the total raw fuel charged, and lowering the cohesive zone level. The present inventors first analyzed the transition of [Si] over a predetermined period while keeping the hot metal temperature constant, as [Si] has a strong correlation with furnace heat (hot metal temperature), and determined that [Si] fluctuates. We extracted the factors.

As a result, various analyzes were attempted, such as stratifying the relationship between total charge SiO ₂ and [Si] by total charge CaO/SiO ₂ , but the relationship between the two only showed a random distribution.
It became clear that there was no particular correlation between the total charge SiO ₂ and the [Si] level. Therefore, we investigated the relationship between coke-derived SiO ₂ and [Si] from the viewpoint that SiO ₂ in the coke ash gasifies into SiO ₂ at high temperatures and [Si] migrates into the metal through reaction with droplets (Fig. 1). )
([Si] value at pig t = 1520 ± 2℃), the relationship between SiO ₂ and [Si] in the coke burned in front of the tuyere, which was controlled by adjusting the air temperature and air humidity (Figure 2) ( [Si] value
at pig t=1520±2°C).

From these relationships, SiO ₂ in the coke system is [Si]
It is an important factor that determines the level, and [Si] =
In the low [Si] pig blast production of the present invention aiming at 0.30% or less, it has been found that the former is preferably 24 Kg/t-p or less, and the latter is required to be 13 Kg/t-p or less.

On the other hand, in the high temperature range below the level of the cohesive zone where SiO ₂ in the coke is contained in the pig iron through a series of reactions,
We investigated and analyzed the relationship between [Si] and the distance (H) proposed by Kitaev, which is considered to indicate the macroscopic cohesive zone height, when SiO ₂ is 12 to 13 kg/t-p. The results are shown in FIG. 3 ([Si] value at pig t=1520±2°C) and FIG. 4 ([Si] value at pig t=1520±2°C).

Kitaev's H used in the present invention is "The
Pergamon Prese” 1967 edition includes “Heat”
BI Exchange in Shoft Fuxnace”
It was calculated using the following formula proposed in a paper published by Kitaev, Yu.G. Yarashenko, and VDSuchkov.

H=3PC _s 〓 _b /h _v (1-C _s G _s /C _g G _g ); [m] Where, P: Volume velocity of solid [m ³ /m ²・hr), C _s : Volume velocity of solid Specific heat [cal/g, °C] γ _b ; Bulk density of solid [Kg/m ³ ], h _v ; Heat transfer coefficient per unit layer volume [kcal/m ³・hr・℃] G _s ; Mass flow rate of solid [Kg/hr] C _g ; Specific heat of gas [kcal/Nm ³・℃] G _g ; Flow rate of gas [Nm ³ /hr] Kitaev et al. Considering that the height necessary for the exchange efficiency to reach a certain value is important, the distance from the solid inlet to the point where the solid temperature reaches 95% of the gas temperature, that is, from the stock line in the blast furnace to the macroscopic fusion The distance to the belt is given by the above formula.

In the case of a blast furnace, P included in the right side of the equation is the rate of descent of the charge, and C _s G _s /C _g G _g is the heat capacity flow rate ratio of the charge and gas. H ₁ is a parameter that theoretically includes these two parameters, and the smaller the value, the easier the solid is heated, and in the case of a blast furnace, the degree of heat exchange is greater.
Therefore, in the present invention, a parameter H is used instead of the descending speed of the charge and the heat capacity flow rate ratio for the position of the cohesive zone existing between the stock line and the tuyere. Note that h _v in the equation has a small range of change in value under current blast furnace operating conditions and has little effect on heat exchange, so it is treated as a constant (3000 kcal/m ³ hr ℃).

As is clear from the figure, as Kitaev's H increases, [Si] shows a tendency to decrease, and [Si] = 0.30%.
In order to blow the following low [Si] pig iron, the cohesive zone must be adjusted to 55% or more (15 m
(above)) It has been found that it is necessary to decrease preferably to 65% or more.

Operate based on this knowledge and review the results.
The relationship between Kitaev's H and [Si], hot metal temperature, and tuyere tip temperature was investigated and studied. The results are shown in FIG.

Recent changes in resource conditions and values have required the use of many new technologies for blast furnace operations, and typical technological means include increasing air temperature, dehumidifying air, and reducing oil injection. This increases the temperature at the tuyere tip, leading to a decrease in the fuel ratio and an increase in the heat flow ratio, which ultimately increases Kitaev H, which tends to help solve the problems of the present invention.

However, if the operation is simply continued under these conditions, [Si] will never be less than 0.35, as is clear from lines A and B shown in Figure 5, and no clue will be found to solve the problem. On the other hand, if each of the above conditions is adjusted and controlled within a satisfactory range, [Si] becomes 0.30% or less, as is clear from line C shown in FIG. 5, and the objective can be achieved.

That is, the present invention maintains the tuyere tip temperature at 2400° C. or higher and reduces the cohesive zone position by 55% or more, preferably 65% or more, thereby shortening the dropping reaction time. Adjust SiO gas to the minimum amount required,
In order to control this, the absolute amount of SiO ₂ generated from the coke burned at the tuyere tip, which is the direct cause of this, was reduced to 13 kg/t.
By reducing Si to below p, the transfer of Si to pig iron is suppressed, so even though the hot metal temperature is maintained at a moderately high level and the heat level in the lower part of the furnace is secured, [Si] is not as expected. This makes it possible to easily obtain molten steel whose composition has been adjusted without removing [Si] during the integrated pig steel process. By continuing blowing under these conditions, the inventors continue to supply pig iron that has achieved the intended purpose, but if any of the conditions are not satisfied, it is difficult to stably produce pig iron with the target [Si]. As a result, smooth and stable operations were not possible.

[Brief explanation of drawings]

Figure 1 shows the relationship between SiO ₂ in the coke charged to the blast furnace and Si in the pig iron, and Figure 2 shows the relationship between SiO ₂ in the coke burned before the tuyere of the blast furnace and Si in the pig iron. Figures 3 and 4 are diagrams showing the relationship between Kitaev's H and Si in pig iron, and Figure 5 is a diagram showing the relationship between Kitaev's H, Si in pig iron, hot metal temperature, and tuyere tip temperature. This is a diagram.

Claims (1)

[Claims] 1. The amount of coke burned at the tip of the blast tuyere is adjusted to the amount of coke burned at the tip of the tuyere such that SiO ₂ in the coke is 13 kg or less per ton of pig iron, and the temperature at the tip of the tuyere is adjusted.
Adjusted to 2400℃ or higher and Kitaev's H = Distance from stock line to macroscopic cohesive zone position (m) / Distance from stock line to blowing tuyere (
A method for producing low-silicon pig iron, characterized by controlling m)×100 to 55% or more, preferably 65% or more. 2. The method for producing low-silicon pig according to claim 1, characterized in that coke containing SiO ₂ of 24 kg or less per pig iron tonne is used.