JP2001279318A - Method for dephosphorizing molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize reduction in the cost of an auxiliary material such as lime, and the shortening of a treating time by holding molten iron temperature to a suitable range in a dephosphorizing treatment with a converter type refining furnace and stabilizing the phosphorus distribution ratio at the end point time to a high level. SOLUTION: While continuously measuring the molten iron temperature in the converter type refining vessel, at least one or more conditions among an oxygen supplying condition, a bottom-blown stirring condition, a supplying amount or a supplying timing of the auxiliary material and a treating completion timing thereof, are decided based on the measured temperature. While holding the molten iron temperature from the starting to the completing of the oxygen supplying treatment to 1,210 deg.C-1,390 deg.C, the iron oxide concentration in slag when the oxygen supplying treatment is completed, is regulated to >=9 mass %.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dephosphorizing hot metal in which dephosphorization of hot metal is performed in a converter type refining vessel such as a top-blowing converter, an upper-bottom-blowing converter, a bottom-blowing converter, or an AOD. .

[0002]

2. Description of the Related Art Since the dephosphorization reaction in the hot metal pretreatment can proceed at a lower temperature than the reaction in the molten steel stage, the exothermic dephosphorization reaction can advantageously proceed. However, when the hot metal temperature is low, the rate of slag slag formation decreases, so in order for the dephosphorization reaction to proceed efficiently, slag slag formation can be sufficiently maintained and operation is performed within a range where reaction efficiency is good. It is important to control the conditions.

[0003] As a cooling means for controlling the hot metal temperature, there are means such as using iron ore (endothermic oxidation reaction) as an oxygen supply source and increasing the mixing ratio of scrap.
Further, as the heating means, there are means for increasing the ratio of gaseous oxygen (exothermic oxidation reaction) and for oxidizing and burning by adding a fuel such as a carbon material. Conventionally, converters that have been used mainly for the purpose of decarburization and refining are designed with a furnace volume of 5 to 10 times the charged volume so as to be able to cope with the intense splash generated during decarburization. In addition, the furnace has been used as a dedicated furnace for hot metal dephosphorization because of the relatively large operating margin against the operation hindrance caused by forming. As an example of hot metal dephosphorization using a converter, as shown in Japanese Patent Application Laid-Open No. 63-195209, after hot dephosphorization is completed, hot metal is once poured and decarburized in a different decarburization converter. And Japanese Patent Application Laid-Open No. 7-24
As disclosed in Japanese Patent No. 2922, there is a method in which waste is once discharged after completion of the dephosphorization treatment and decarburization treatment is performed in the same converter.

[0004]

With respect to dephosphorization of hot metal by a converter type refining vessel, the rate of slag slag is made high to increase the mass transfer rate on the slag side, and the hot metal temperature is always maintained at a low temperature. It is important to. In the conventional operation, the heat balance up to the end of the treatment is calculated in advance from the initial hot metal composition and the temperature, and the scrap mixing ratio, iron ore, CaO
Although the input amount and input timing of auxiliary materials are determined, in normal operation, the dispersion of heat dissipation between tap taps,
A large variation is included in the heat balance due to a change in the amount of residual slag and the amount of metal in the furnace carried over from the previous charge. To correct these temperature variations, a thermocouple probe is attached to the sub lance to measure the temperature during processing, and based on the measured temperature, the acid supply conditions and auxiliary material input amount etc. are adjusted to the target temperature. The operation to determine

However, the temperature measurement using a sublance probe is expensive because an expensive consumable probe is used, and the measurement can be performed only once every few minutes. There are limitations in terms of target and mechanical ability. Therefore, before the measurement of the hot metal temperature, it is difficult to detect the temperature variation occurring between the measurements, and thus it has been difficult to always keep the hot metal temperature in the dephosphorization process within a certain range. Also, the temperature range maintained during the dephosphorization treatment and the appropriate oxygen potential in the slag after the treatment were unclear. The present invention provides a method for dephosphorizing hot metal using a converter type refining vessel, while maintaining the hot metal temperature range during the process in a range advantageous for dephosphorization, the oxygen potential in the slag at the end of the process is high iron oxide without rephosphorization, By controlling the concentration, it is possible to significantly reduce the cost of auxiliary materials such as quicklime and provide a means for enabling a short-time treatment.

[0006]

The present invention, which is means for solving the above problems, is as follows.

[0007] While continuously measuring the hot metal temperature in the converter type refining vessel, at least one condition of an acid supply condition, a bottom blow stirring condition, a supply amount or supply timing of an auxiliary material, and a processing end timing based on the measured temperature. The above determination was made, and the hot metal temperature from the start to the end of the acid supply treatment was set to 1210 ° C. or more and 13
A method for dephosphorizing hot metal comprising maintaining the iron oxide concentration in slag at the time of completion of the acid supply treatment at 9% by mass or more while maintaining the temperature at 90 ° C or lower.

In the above method, it is desirable to measure the iron oxide concentration of the slag at least once before or during the dephosphorization treatment.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. This diagram schematically shows a converter during hot metal dephosphorization.

A hot metal 2 is charged into a converter 1, and while blowing oxygen gas 4 from an upper blowing lance 3, a bottom blowing tuyere 5 is formed.
More stirring gas 6 is introduced. Oxygen introduced into the furnace from the top blowing lance 3 and the bottom blowing tuyere 5 separates P in the hot metal into P ₂ O ₅ by oxidation reaction in the slag 7,
C, Fe, etc. in the hot metal are also oxidized and separated from the hot metal in the form of CO gas, FeO, or the like. Further, auxiliary materials such as quicklime and iron ore necessary for the dephosphorization treatment are appropriately supplied to the furnace hopper 1.
It is added into the furnace from 0.

The hot metal temperature changes successively throughout the process due to changes in reaction heat generated by oxidation, secondary combustion, etc., heat dissipated in the furnace, gas sensible heat discharged from the exhaust duct 8, and the like. It is continuously measured by a temperature sensor 9 provided on the body. The temperature sensor 9 includes a glass fiber (not shown) for transmitting light from inside the stainless steel tuyere to a two-color thermometer provided outside the furnace.
It is desirable to continuously measure the temperature while purging Ar gas from inside the tuyere to avoid intrusion of hot metal into the tuyere.

At this time, the appropriate hot metal temperature range is 1210
If the hot metal temperature during processing is expected to be outside the appropriate range based on extrapolated values of past temperature changes while performing continuous temperature measurement, the acid supply conditions (lance height The acid supply rate, the supply amount of each system for the lances that can supply gas of multiple systems), bottom blowing stirring conditions (bottom blowing gas flow rate, bottom blowing gas type), supply amount and supply timing of auxiliary materials, processing end Determine the timing and maintain an appropriate range. If the hot metal temperature is expected to fall below the lower limit, an increase in the secondary combustion rate (increase in the lance height or an increase in the oxygen flow rate in the secondary hole of the secondary combustion lance), an increase in the top blowing acid transfer rate,
Heating is promoted by lowering the ratio of the bottom blown gas, lowering the ratio of endothermic gas such as CO ₂ , and adding a heating material such as carbonaceous material or aluminum. On the other hand, when the hot metal temperature is expected to exceed the upper limit, a decrease in the secondary combustion rate (a decrease in the lance height or a decrease in the oxygen flow rate in the secondary hole of the secondary combustion lance), a decrease in the top-blow acid transfer rate, Cooling is promoted by increasing the ratio of bottom blown gas, increasing the ratio of endothermic gas such as CO ₂ , and adding a coolant such as iron ore and scrap. It is possible to maintain an appropriate temperature range by using such a temperature raising / lowering means.

Further, by ensuring that the iron oxide concentration in the slag after the dephosphorization treatment is 9% by mass or more, an efficient dephosphorization reaction can proceed. The iron oxide concentration defined here is the concentration of iron oxide contained in slag in the form of FeO and Fe ₂ O _{3. In} the case of iron oxide coexisting with hot metal, the main component is F
Since it is eO, T.O. It can also be estimated from the Fe analysis value by the following equation.

Iron oxide concentration (% by mass) = t. Fe
(Mass%) × (55.9 + 16.0) /55.9 Here, 55.9 and 16.0 are the atomic weight of iron and the atomic weight of oxygen, respectively.

Appropriate ranges were set for the hot metal temperature during the treatment and the iron oxide concentration after the treatment. In the converter type hot metal dephosphorization treatment, the slag is usually operated at a slag basicity (mass% CaO / mass% SiO ₂ ) defined by the weight ratio of CaO and SiO ₂ in the slag of around 1.5. When the temperature of the hot metal during the treatment is lower than 1210 ° C., the slag conversion rate of the slag is reduced, and the solubility of P ₂ O ₅ once separated and removed in the molten slag in the slag is remarkably reduced to be reduced to P in the hot metal. Rephosphorization occurs which remelts. Also, 1
Even if the temperature is in the range of 390 ° C. or higher, phosphorus reversion occurs due to the temperature rise. Therefore, if the upper limit or lower limit of the hot metal temperature is exceeded during the dephosphorization treatment, the P concentration once reduced by the dephosphorization increases again due to the rephosphorization. Maintain proper temperature throughout. The iron oxide concentration at the end of the dephosphorization treatment was 9% by mass.
In the following regions, a high phosphorus distribution ratio cannot be obtained even when operating in the above-mentioned appropriate temperature range. This is because, since the oxygen potential in the slag mainly controlled by FeO is low, the phosphate capacity of the slag is reduced and sufficient dephosphorization ability cannot be secured. Although there is no upper limit on the appropriate iron oxide concentration, the distribution ratio does not decrease due to the increase in iron oxide concentration with respect to ordinary hot metal dephosphorization, but from the viewpoint of refractory protection and maintenance of iron yield. Considering this, the economic effect is considered to be relatively small in the range exceeding 45% by mass.

The iron oxide concentration in the slag increases when the hot metal temperature is high, and tends to decrease when the hot metal temperature is low. On the contrary, when the hot metal temperature is low, the iron oxide concentration tends to increase. It is effective to use the continuous analysis values for guidance to determine the iron ore input timing and amount, the processing end timing, and the like. Furthermore, since iron oxide in the slag carried over from the previous charge also affects the iron oxide composition in the final slag, a rapid analysis of the iron oxide concentration in the slag is performed before or during the dephosphorization treatment, and the oxidation is performed. The relationship between the iron concentration analysis value and the iron oxide concentration after the dephosphorization treatment based on the operating data such as the average hot metal temperature during treatment, the amount of acid supply, the flow rate of the bottom-blown stirring gas, and the amount of iron oxide addition, is represented by a multiple regression equation. Predict and determine the appropriate iron ore addition amount so that the iron oxide concentration in the slag becomes 9% by mass or more of the lower limit, improve the accuracy of the iron oxide concentration prediction value at the end of the treatment, and improve the iron oxide concentration. It is effective to avoid the deviation from the lower limit of the above, and to avoid an increase in the cost of auxiliary materials and a temperature loss due to the addition of iron ore more than necessary.

As a method of estimating the iron oxide concentration in the slag after the dephosphorization treatment using the measured value of the iron oxide concentration in the slag, in addition to the multiple regression method, a statistical estimation method such as a neural network method, a reaction kinetics method, and the like. May be used, or a method based on a simple correlation at the end of the dephosphorization process with the analysis value of the slag collected during a certain period of time during the process may be used. As an analytical method for this purpose, online measurement of iron oxide activity in slag using an oxygen concentration cell such as zirconia, or on-site iron and steel as shown in Vol. 85 (1999) No. 2, page 86 It is desirable to control the concentration of iron oxide in the charge using a rapid X-ray fluorescence analysis or the like. The iron oxide concentration in the slag can be accurately controlled by performing a plurality of measurements such as before the treatment and immediately before the end of the treatment. However, the measurement takes several minutes at one time, which leads to an increase in analysis cost. Therefore, usually, the dephosphorization treatment using a converter type refining vessel performed within 20 minutes or less takes 1 to 5 times. Is preferred.

[0018]

EXAMPLE A 6-ton top-bottom blow test was conducted using a converter.

Table 1 shows the component ranges of the hot metal before treatment used in the test operation. Top blowing acid transfer rate is 700Nm ³ / h
Under the basic conditions, nitrogen of 60 Nm ³ / h was blown into the bottom blow, and 180 kg (30 kg / t) of quicklime was initially charged as an auxiliary material. The hot metal temperature is continuously measured by a two-color thermometer, and when it is predicted that the temperature will drop below the target temperature, the top blowing acid feed rate is increased to an upper limit of 1000 Nm ³ / h, and the temperature is expected to rise above the target temperature When this was done, the top blowing acid transfer rate was reduced to a lower limit of 300 Nm ³ / h, and when it was necessary to increase the iron oxide concentration, iron ore was charged. The processing time was about 12 minutes ± 1 minute for all charges.

[0020]

[Table 1]

FIG. 2 shows the minimum temperature (●) and the maximum temperature (black triangle) of the hot metal during the dephosphorization treatment obtained by continuous temperature measurement.
Phosphorus distribution ratio (P concentration in slag (mass%) / P concentration in hot metal (mass) determined from analytical values of hot metal component and slag component after treatment
%)) Is shown on the vertical axis. For comparison, continuous temperature measurement was used only for temperature recording and was not used for guidance, and the phosphorus distribution ratio obtained from the test result of batch temperature measurement using a sublance was marked with a circle.
(Minimum temperature during processing) and Δ (highest temperature during processing). As a result of the test, when the guidance operation by continuous temperature measurement was performed, the hot metal temperature during the dephosphorization treatment was adjusted to the appropriate range of 1210 to 1390
In contrast, the conventional method, which does not reflect the results of continuous temperature measurement in the operation, could have a maximum or minimum temperature outside the proper range, and the phosphorus distribution ratio was less than 100. It can be seen that it has decreased. In addition, even when the temperature range during the operation is within the proper range, it can be seen that the phosphorus distribution is low for the charge in which the iron oxide concentration in the slag after the treatment is less than 9% by mass. In order to improve the accuracy of making the iron oxide concentration in slag 9% by mass or more, the iron oxide concentration in slag is measured using a zirconia-type oxygen sensor, and the target value of iron oxide concentration is set in the charge where the iron ore input amount is adjusted according to the measured value. Can be reduced to 6.1% by mass, and the controllability is greatly improved as compared with the standard deviation of 11.4% by mass of the actual value when the oxygen potential measurement was not performed.

Since the effects shown in FIG. 2 have been clarified, the conventional unit of quick lime 43 kg / t and the processing time of 1 required conventionally to stably achieve the phosphorus distribution ratio> 100.
5.5 minutes or more could be achieved at 30 kg / t and less than 13 minutes, respectively, confirming the effects of saving auxiliary materials and shortening the processing time.

[0023]

According to the present invention, since the phosphorus distribution ratio of the dephosphorization treatment in the converter type refining vessel can be stably maintained at a high level, the cost of auxiliary materials such as quicklime can be reduced and the cost can be reduced. At the same time, productivity can be improved by shortening the processing time.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an example of an apparatus for carrying out the present invention.

FIG. 2 is a diagram showing a distribution ratio of phosphorus obtained as a result of the practice of the present invention in comparison with a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Converter 2 Hot metal 3 Top blowing lance 4 Oxygen gas 5 Bottom blowing tuyere 6 Stirring gas 7 Slag 8 Exhaust duct 9 Temperature sensor 10 Furnace hopper

 ──────────────────────────────────────────────────の Continued on the front page F term (reference) 4K002 AB01 AB04 AC07 AC08 AD02 AD05 AE01 AF02 AF04 BF05 4K014 AA03 AB03 AB04 AB18 AB21 AC01 AC08 AC13 AC16 AC17 AD00

Claims (2)

[Claims] 1. While continuously measuring the hot metal temperature in a converter type refining vessel, at least one of an acid supply condition, a bottom blow stirring condition, a supply amount or supply timing of an auxiliary material, and a processing end timing based on the measured temperature. One or more conditions are determined, and the hot metal temperature from the start to the end of the acid supply treatment is set to 1210 ° C. or more and 13
A method for dephosphorizing hot metal comprising maintaining the iron oxide concentration in slag at the time of completion of the acid supply treatment at 9% by mass or more while maintaining the temperature at 90 ° C or lower. 2. The hot metal dephosphorization treatment method according to claim 1, wherein the iron oxide concentration of the slag is measured at least once before or during the dephosphorization treatment.