JPH0649889B2 - Hot metal dephosphorization method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for dephosphorizing hot metal.

[Prior Art] Conventionally, the dephosphorization step has been performed in the converter refining step, but there has been a problem that dephosphorization in the steelmaking stage significantly reduces the productivity of steelmaking. As a countermeasure to this, recently, hot metal dephosphorization is performed outside the furnace before charging the converter (hot metal pretreatment).
Is being actively done. In particular, in the less slag blowing of the converter (the blowing is performed mainly only for decarburization, slag is hardly formed), the medium solvent can be reduced if the phosphorus in the hot metal is sufficiently reduced by the hot metal pretreatment. Therefore, the amount of manganese ore input can be increased and the manganese yield can be improved. Thus, if the phosphorus in the hot metal after the pretreatment is too large, it increases the amount of the solvent medium in the converter,
Although the manganese yield is reduced, even if it is reduced less than necessary, it does not contribute much to the reduction of the solvent content, and does not contribute much to the improvement of the manganese yield. Is caused, which is not preferable. Therefore, there is an optimum value for the amount of phosphorus (hereinafter abbreviated as [P]) in the hot metal after the hot metal pretreatment, and operations are performed to control the hot metal pretreatment process with this optimum value as a target. There is.

The method is to measure the [P] in the hot metal and the hot metal temperature, calculate the target amount of [P] after hot metal pretreatment and the amount of the necessary medium-melting material from these amounts, and add it The process is to end.

[Problems to be Solved by the Invention] However, in the conventional method, the relation between the target value of [P] in the hot metal, the hot metal temperature, the target value of [P] after the hot metal pretreatment, and the necessary medium-melting material has been determined in the past There is a limit to the accuracy of the calculation formula because it is obtained by regression analysis from the data in. For this reason, the accuracy of hitting the target value of [P] after the pretreatment was poor, and it was not always satisfactory.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hot metal dephosphorization method in which the value of [P] after pretreatment has an accuracy sufficient for a target value.

[Means and Actions for Solving the Problem] In the hot metal pretreatment step, the object is to measure [P] in the hot metal before starting the pretreatment and hot metal temperature, and to obtain these values and [P] after the pretreatment. The amount of the solvent material that is less than the amount calculated based on the target value of is added, and the time transition of [P] determined by these values is predicted, and after the start of the preliminary treatment, the treatment time ratio is 60%. When the above is reached, [P] is measured using a phosphorus sensor which is immersed in hot metal to measure the phosphorus component [P] in the hot metal, and this measured value and the predicted [P] time transition It is achieved by calculating the amount of the additive medium material required to hit [P] after the pretreatment to the target value based on the difference from the estimated value of [P], and adding it. It When the value of [P] measured when the treatment time rate is 60% or more is lower than the estimated value, there is no room for adding the solvent, and the [P] concentration decreases more than necessary. However, in the present invention, since the amount of the medium-dissolving material to be charged in advance is set to be smaller than the calculated value, the value of [P] measured during the processing is always higher than the estimated value, and the medium Additional injection of molten material is performed.

Therefore, even if there is an error in the initial amount of the solvent material to be charged in advance, this error is measured by measuring [P] during the pretreatment process, and the measured value and the time of the predicted [P] are measured. Based on the difference from the estimated value of [P] obtained from the transition, it is corrected by calculating the amount of additive-solvent required to bring [P] after pretreatment to the target value and adding it. It
Then, the difference between the [P] concentration after the dephosphorization treatment and the target [P] concentration becomes small, and the management accuracy of the [P] concentration in the hot metal after the dephosphorization treatment is improved.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1 to 6. In FIG. 1, the vertical axis represents [P], and the horizontal axis represents the time from the start to the end of the hot metal pretreatment in percentage (processing time rate). The processing time is predetermined according to the hot metal temperature and the like. Processing time rate 0
The value of [P] in indicates the measured [P] in the hot metal before the hot metal pretreatment, and the value of [P] at the treatment time ratio 100 is the target value of the [P] in the hot metal after the pretreatment. Corresponding to. The figure shows that [P] changes with time when a medium-melting material calculated based on the target value of [P] in the hot metal before starting the pretreatment, hot metal temperature and [P] after hot metal treatment is added. It shows how it changes. [P] in the hot metal before the start of pretreatment, the relationship between the hot metal temperature and the target value of [P] after the hot metal treatment, and the amount of the necessary medium-melting material, and the temporal relationship of [P] shown in FIG. The transition (hereinafter referred to as the reference line) is obtained in advance by regression analysis or the like based on past operation data. FIG. 2 shows the results of measuring [P] with a phosphorus sensor during the pretreatment process. In this example, [P] is measured at a processing time rate of 60%, and the measured value is higher by A% than the set value of [P] calculated from the reference line. . According to this difference A, the amount of the solvent material to be additionally charged is calculated. For example,
In order to reduce [P] by 1%, a [k
g], if this is necessary, in this case, 1 t of hot metal
Therefore, it is only necessary to add A * a [kg] of the solvent material.
The timing of measuring [P] is not limited to the time of the processing time ratio of 60%, and may be selected as late as possible when [P] does not decrease more than necessary. This point can be known by the statistical data in actual operation.

FIG. 3 shows the work in the actual operation,
It shows what kind of work is performed according to the processing time rate. First, prior to starting the pretreatment work, analysis of hot metal components and measurement of hot metal temperature are performed. [P] in the hot metal before the start of the pretreatment, the hot metal temperature, and the medium melt material calculated based on the target values of [P] after the hot metal treatment were added,
Then, the hot metal pretreatment is started. As the pretreatment progresses, quick lime, scale, fluorspar, etc. are added. When the treatment time rate reaches 60%, [P] is measured by the phosphorus sensor, and the amount of the solvent material added according to the difference from the estimated value of [P] calculated from the reference line is added. To do.
After that, when the processing time rate reaches 100%, the processing ends.

FIG. 4 is a vertical sectional view of a P sensor used in the method of the present invention. In this figure, 1 is hot metal to be measured, 2 is a potentiometer, and 3 and 4 are electrodes. Further, 5 is a reference substance, 6 is a solid electrolyte having oxygen ion conductivity at high temperature, and 7 is a coating agent. The operation of the P sensor thus configured will be described. As is well known electrochemically, the potential difference EMF appearing on the potentiometer 2 indicates the oxygen partial pressures of the reference substance 5 and the hot metal 1 as P ₀₂ (I) and P ₀₂ (II), respectively.
Then, it is expressed by the following equation.

EMF =-(RT / 4F) 1n [P ₀₂ (I) / P ₀₂ (II)] where F, R, and T are the Faraday constant, the gas constant, and the absolute temperature of the hot metal, respectively. Oxygen partial pressure P of reference substance 5
₀₂ (I) is determined by the reference substance and its oxide, while the oxygen partial pressure P ₀₂ (II) of the hot metal changes depending on [P]. Therefore, know [P] by measuring the EMF. Can be done. In order to remove the influence of phosphorus oxide in the hot metal on the oxygen partial pressure P ₀₂ (II) of the hot metal, P ₂ O ₅ is coated on the outside of the solid electrolyte 6 as a coating agent. The influence of the temperature can be understood by the thermometer using a thermocouple at the time of measurement, and is therefore taken into consideration in the measured value of [P] by a predetermined calculation formula.

[P] is measured at the end of the hot metal pretreatment by the phosphorus sensor as described above.

FIG. 5 is a graph showing the change of [P] during the pretreatment,
An example in which the [P] level after pretreatment is controlled to 0.012% for two types of [P] levels before treatment of 0.125% and 0.115% is shown. The vertical axis represents the percentage of [P], and the horizontal axis represents the amount of oxygen blown in per ton of hot metal. As is clear from this figure, the end point [P] is accurately controlled by the measurement of [P] before the dephosphorization treatment. The operating conditions at this time are as follows.

Pretreatment [Si]; ≦ 0.20%, CaO / SiO 2; 4.0~4.5%, the temperature of the processed molten iron; 1320 ° C., using oxygen; 8.6Nm ³ / t, after the treatment [P]; 0.012%, Treatment time: 25 min, basic unit of solvent (kg / t); CaO: 11.0, scale: 25, fluorspar: 3.0, slag: 10.

FIGS. 6a and 6b are graphs showing variations in [P] with respect to the target value after the completion of the dephosphorization treatment in the above-described method according to the present invention and the conventional method. 6A and 6B correspond to the conventional example and the present embodiment, respectively. In the figure, A, B, and C correspond to three different targets [P], and their values and their respective standard deviations σ are as shown in Table 1. The reduction of the standard deviation σ according to this embodiment directly represents the effect of the present invention.

[Effect of the Invention] According to the present invention, the amount of the solvent material charged in advance is set smaller than the calculated value, and the difference between the phosphorus concentration measured during the treatment and the estimated value at that time predicted before the treatment is started. On the basis of the above, since the additional solvent is added, the fluctuation range of the phosphorus concentration after the dephosphorization treatment with respect to the target value becomes extremely small.

[Brief description of drawings]

FIG. 1 is a diagram showing a change in [P] from the start to the end of hot metal pretreatment, FIG. 2 is a diagram showing a difference between a measured value and an estimated value of [P] in the present invention, and FIG. 3 is a diagram showing the present invention. FIG. 4 is a diagram showing an operation for carrying out the present invention, FIG. 4 is a vertical sectional view of a P sensor used in the method of the present invention, FIG. 5 is a graph showing changes in [P] during dephosphorization treatment, and FIG. [Fig. 4] is a graph showing a deviation of [P] from a target value after completion of dephosphorization treatment. 1 ... hot metal, 2 ... potentiometer, 3,4 ... electrode, 5 ...
Reference substance, 6 ... Solid electrolyte, 7 ... Coating agent.

Claims (1)

[Claims] 1. In the hot metal pretreatment step, the phosphorus concentration in the hot metal and the hot metal temperature before starting the pretreatment are measured, and the amount calculated based on these values and the target value of the phosphorus concentration after the pretreatment is more than the amount calculated. A small amount of solvent is added, and the time course of the phosphorus concentration determined by these values is predicted. Further, after the pretreatment is started, when the treatment time rate becomes 60% or more, the medium is immersed in the hot metal. The phosphorus concentration was measured using a phosphorus sensor for measuring the phosphorus component concentration in the hot metal, and the preliminary treatment was performed based on the difference between this measured value and the estimated value of the phosphorus concentration obtained from the predicted time course of the phosphorus concentration. A hot metal dephosphorization method, characterized in that the amount of additive medium material required to bring the subsequent phosphorus concentration to a target value is calculated, and then added.