KR101608808B1 - Method for Dephosphorizing of Molten steel - Google Patents

Abstract

The present invention relates to a method for measuring the initial temperature of a molten iron and a content of silicon; A first blowing step in which the weight ratio of gaseous oxygen to solid oxygen charged in the talline blowing process in the Tallinn preheater is 90: 10 to 100: 0; A second blowing step in which the weight ratio of gaseous oxygen to solid oxygen injected during the talline blowing process is 20:80 to 30:70; And finishing the tallinn refining process when both the heating rate of the charcoal line and the content of silicon contained in the charcoal line reach a target value.

Description

{Method for Dephosphorizing of Molten steel}

The present invention relates to a method for treating a molten iron, and more particularly, to a molten iron tallining method capable of removing molten iron from the molten iron and raising the temperature of the molten iron.

Today, the steelmaking process using hot metal made in blast furnace is very common compared with electric furnace steelmaking. The blast furnace process is a process to produce reduced iron from raw materials such as iron ore, coke and limestone. It has advantages of low cost and high productivity compared to other iron source production methods. In general, however, impurities derived from iron ores and cokes such as silicon, phosphorus, and sulfur in addition to carbon are contained in the molten iron produced in the blast furnace at a concentration exceeding the allowable range of the final product, thereby removing the impurities before the steelmaking process . This is called Hot Metal Pretreatment and has been adopted by many steel mills since the 1970s with the aim of alleviating the burden of the converter process.

The pretreatment of the molten iron is largely divided into degasification, talline and desulfurization, and the proper treatment sequence is taken according to the conditions such as the temperature of the molten iron and the progress of the subsequent process. The degreasing, talline and desulfurizing processes are different from each other There are also conflicting conditions. Therefore, it is necessary to judge conditions of each refining process individually when determining the process sequence of the preliminary process.

In addition, the technology for preliminary treatment in open ladle has made a lot of progress since the 1980s, and reaction physical chemistry and slag conditions are well established. In fact, it has been experimentally proven several times that the degassing is preceded by the difference in oxygen affinity between silicon and phosphorus and the talline proceeds only at the silicon concentration of 0.2% or less. The optimum basicity of talline slag is also widely applied around 4.0 .

However, the initial conditions of the molten iron such as the silicon concentration and the arrival temperature in the molten iron greatly influence the pre-treatment process, but they are not easy to control depending on the raw material and the blast furnace condition, and therefore must always be considered. Particularly, since the initial silicon concentration acts as a burden of the pre-treatment and the conversion operation such as increasing the amount of slag, low concentration is preferred, and columnar degassing is generally adopted in many steelworks for introducing solid oxygen in the column at the time of leaving at the highway.

However, there is a problem that the columnar degassing also fails to set the desired temperature by lowering the temperature of the molten iron. Therefore, it is urgent to research and develop a technology that can adjust the temperature of the molten iron to be suitable for the conversion process and increase the efficiency of degasification and talline reaction.

Korean Patent Publication No. 10-2013-0034150

The present invention is to provide a method for increasing the temperature of molten iron and obtaining a talline effect at the same time, since the effect of increasing the efficiency of talline and the temperature of molten iron in the molten talline refining process are in conflict with each other do.

One aspect of the present invention is a method for measuring the temperature of a molten iron, comprising the steps of: measuring an initial temperature of the molten iron and a content of silicon; A first blowing step in which the weight ratio of the gaseous oxygen fed into the talline blowing furnace in the talline blowing process is greater than the weight ratio of the injected solid oxygen; A second tinning step in which the weight ratio of the gaseous oxygen introduced is smaller than the weight ratio of the solid oxygen fed in the talline recycling process; And finishing the talline refining process when both the heating rate of the charcoal line and the content of silicon contained in the charcoal line reach a target value.

The weight ratio of the gaseous oxygen to the solid oxygen in the first kneading step is 90:10 to 100: 0, and the weight ratio of the gaseous oxygen to the solid oxygen in the second kneading step is 20:80 to 30:70. Talline method can be provided.

The first tinning step and the second tinning step are continuously performed, and the boundary between the first tinning step and the second tinning step is provided with a charring tinling method in which the rate of silicon reduction of the molten iron is initially 0.1 to 0.4 can do.

Further, the target value is a difference between the temperature and the initial temperature after the last stage of talline culling, the heating rate is 55 to 80 ° C, the silicon content is 0.1 to 0.3 % ≪ / RTI > by weight.

According to one aspect of the present invention, the molten talline method can obtain both the talline effect and the temperature elevating effect by controlling the ratio of the gaseous oxygen to the solid oxygen during the talline refining process of the molten iron.

FIG. 1 is a flowchart illustrating a procedure of a chartered tallinn method according to an embodiment of the present invention.
FIGS. 2 (a) and 2 (b) are graphs showing the concentration behavior of silicon (Si) and phosphorus (P) in a talline refining process and show the first and second refining steps according to the embodiment, respectively.
FIG. 3 is a graph illustrating a comparison of the talline ratio with the conventional method using the molten talline method according to an embodiment of the present invention.
FIG. 4 is a graph illustrating a result of comparing the processing time with the conventional method according to an embodiment of the present invention.
FIG. 5 is a graph illustrating a result of comparing a temperature increase by a molten talline method with an existing method according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following embodiments are provided to fully convey the spirit of the present invention to a person having ordinary skill in the art to which the present invention belongs. The present invention is not limited to the embodiments shown herein but may be embodied in other forms. For the sake of clarity, the drawings are not drawn to scale, and the size of the elements may be slightly exaggerated to facilitate understanding.

FIG. 1 is a flowchart illustrating a procedure of a chartered tallinn method according to an embodiment of the present invention. Referring to FIG. 1, a method of measuring a molten iron talline according to an embodiment of the present invention includes a step 100 of measuring an initial temperature and a content of silicon in a molten iron, The second culling step 300 and the second culling step 300 in which the weight ratio of the gaseous oxygen introduced is smaller than the weight ratio of the injected solid oxygen in the first culling step 200 and the talline culling process, And finishing the talline refining process when all of the heating rate of the charcoal line and the content of silicon contained in the charcoal line reach a target value (step 400).

The process of treating the charcoal can be roughly classified into degasification, talline and desulfurization processes, and the appropriate conditions such as temperature are determined according to each process. These conditions take into account the thermodynamic conditions of each component to obtain the desired effect in each process.

The desulfurization step is a step of removing sulfur (S) from the molten iron, and can be removed by using exchange reaction of sulfur in the quick lime and molten iron as shown in the following reaction formula (1).

Scheme 1

CaO (s) + [S]? CaS (s) + [O]? H> 0

Referring to Reaction Scheme 1, it can be seen that the enthalpy of the substance located at the right side is higher, and therefore, it can be seen that the reaction of the above reaction is entirely an endothermic reaction. If the forward reaction is dominant, sulfur (S) in the left port can be removed by exchange reaction with quicklime, and in order to do so, the temperature should be raised and oxygen activity in the molten steel should be low. In particular, if the oxygen concentration of the surface activated element is not sufficiently low, the desulfurization reaction may not easily occur because oxygen is preferentially located at the slag-metal interface.

Further, the degreasing process and the tallin process for removing silicon or phosphorus in the charcoal follow the following Reaction Schemes 2 and 3.

Scheme 2

_{[Si] + O 2 ↔ SiO} 2 (in slag) △ H <0

Scheme 3

2 [P] + 2.5 O ₂ ↔ P ₂ O ₅ (in slag) ΔH <0

Referring to equations (2) and (3) above, it can be seen that the reactions occurring in the decarburization and talline processes are lower enthalpy of entities located at the right end and therefore exothermic. Therefore, it is necessary to lower the temperature so that the positive reaction proceeds. Also, since it is an oxidation reaction to react with oxygen, the higher the oxygen partial pressure in the molten iron, the more the reaction can be led to the reaction.

As discussed above, there is a difference in the reactions taking place in the desulfurization process and in the degassing and talline processes. Therefore, the same process can not simultaneously achieve the purpose of desulfurization and degassing and talline.

Similarly, it can be seen that there is a difference in the reactions occurring in the degassing and talline processes. Particularly, in order to allow silicon (Si) and phosphorus (P) to escape, the bonding with oxygen (O ₂ ) must be preceded as shown in the above reaction formulas 2 and 3. The oxygen affinity of silicon (Si) It can be seen that the talline reaction starts after a substantial part of the silicon (Si) contained in the charcoal is removed. In particular, it is known that the talline reaction begins when silicon (Si) in the charcoal reaches about 0.2% of the weight of the charcoal. Particularly, since the concentration of the initial silicon (Si) causes a problem such as an increase in the amount of slag, a low value may be suitable, and thus, a columnar degassing process in which solid oxygen is introduced, .

However, not only the concentration of silicon (Si) but also the temperature of the molten iron is an important part, which is directly related to the refining efficiency. In particular, it can be seen from the above reaction formulas 2 and 3 that the degassing and tallining process is accompanied by a decarburization process in the furnace after the degassing and tallining process. The higher the value, the better. Thus, this temperature control may be possible by controlling the mixing ratio of gaseous oxygen and solid oxygen. The degassing reaction and the talline reaction using gaseous oxygen are accompanied by an oxidation reaction and can serve to elevate the temperature of the hot water as a whole. In the case of using solid oxygen, reduction of solid containing oxygen such as iron oxide (FeO) Reaction. This reduction reaction corresponds to the opposite reaction of the oxidation reaction and is an endothermic reaction. Therefore, the ambient temperature is lowered. As a result, gas oxygen and solid oxygen can attain the desired reaction effect of degassing and talline reaction, but there may be differences in the effect on the surroundings.

In addition, in the case of solid oxygen, not only the direct contact with the surface of the molten iron but also the oxidation and reduction reaction can be caused even to a certain inside of the molten metal, so that the degassing and the talline reaction can be efficiently performed. On the other hand, And there may be other reactions or parts that can disappear into the air in addition to the desired reaction. As a result, the reaction efficiency of solid oxygen is superior to the reaction efficiency of gaseous oxygen. Therefore, in the case of using only gaseous oxygen in consideration of the transferring temperature of the molten iron, quality of the degasification and tallining process can not be guaranteed. As a result, both the quality of the molten iron and the process efficiency can be maximized by controlling the ratio of solid and gaseous oxygen in the talline process.

FIG. 2 is a graph showing the concentration behavior of silicon (Si) and phosphorus (P) in the Tallinn process. Referring to FIG. 2, although the initial silicon (Si) concentration is in the vicinity of 0.2%, the decalcification progresses predominantly at the beginning of talline. As a result, Even at a concentration of 0.2% or less, it can be seen that silicon having a strong affinity with oxygen initially reacts with a relatively strong driving force.

Accordingly, one aspect of the present invention is to provide a method and apparatus for increasing the gas-oxygen ratio in the first culling step 200 in which the degassing reaction intensively proceeds in the talline curing process and a second culling step 300 in which the talline reaction is relatively prevailing, A method of increasing the ratio of good solid oxygen can be provided. This method can be considered to actively utilize the solid oxygen in consideration of the relatively low reaction efficiency as compared with the degassing reaction and to actively utilize the gaseous oxygen in the degassing reaction in order to obtain the temperature increasing effect .

The weight ratio of gas oxygen to solid oxygen in the first and second kneading steps 200 and 300 is not particularly limited. However, in the first kneading step 200, the weight ratio of gas oxygen to solid oxygen is 90:10 to 100: 0, and in the second blowing step 300, the weight ratio of gaseous oxygen to solid oxygen may be 20:80 to 30:70. More specifically, the present invention will be described through the following experimental examples.

The present invention is also characterized in that the first culling step 200 and the second culling step 300 are performed continuously and the first culling step 200 and the second culling step 300 are performed at the boundary of the first culling step 200 and the second culling step 300, The silicon reduction rate may provide a chartered tallining method that is 0.1 to 0.4 times the silicon reduction rate of the charter at the beginning of the first culling step 200.

2 (a) and 2 (b) are graphs showing the concentration behavior of silicon (Si) and phosphorus (P) in the talline process. 2 (a) and 2 (b), it is generally known that the degassing reaction and the talline reaction proceed at the same reaction rate under the condition that the concentration of silicon (Si) is 0.2% or less. As a result, Despite the fact that the initial silicon (Si) concentration is around 0.2%, it can be seen that degassing prevails rather than talline at the beginning. This is because silicon (Si) has strong affinity with oxygen (O ₂ ) as compared with phosphorus (P), and thus it can be judged that the degreasing reaction has stronger driving force than the talline reaction.

In the first and second kneading steps 200 and 300, the ratio of the gas oxygen to the solid oxygen varies. The criterion for distinguishing the gas oxygen and the solid oxygen is the reaction rate of the talline reaction. If the reaction rate of the talline reaction is decreased by a certain amount or more as compared with the initial stage of the reaction, it can be determined that the first tinning step 200 to the second tinning step 300 have been passed. The reaction rate can be known by the concentration change of silicon (Si), and it can be judged by the instantaneous slope in the graph of FIG. Thus, the initial reaction rate may have a slope of A. If the instantaneous slopes are 30 minutes to 40 minutes in which the amount of decrease in the concentration of silicon (Si) decreases conspicuously, B and C are B and C, respectively, and B and C each have a value of 0.1 to 0.4 times the slope of A . The technician who manages the Tallinn process can use the reference values between B and C according to the situation.

Since the first and second winding stages 200 and 300 can be continuous, when the technician sets the slope B as the reference value, the initial stages a to b are the first winding stage 200 , And b to d may be the second culling step 300. [ Likewise, if the descriptor sets the C slope as the reference value, the initial stages a to c may be the first culling stage 200, and c to d may be the second culling stage 300.

Further, in the present invention, the target value is the difference between the temperature and the initial temperature after the last stage of tallinn culling, the heating rate is 55 to 80 ° C, 0.1 to 0.3% by weight.

The efficiency of the oxygen used in the degassing reaction and the talline reaction, respectively, and the heat input and output are shown in Table 1 below.

Decalcification reaction Talline reaction Solid oxygen Gas oxygen Solid oxygen Gas oxygen Reaction efficiency 70% 35% 14% 7% Heat input per 1 kg 3,100kJ heat generation 7,719kJ heat generation 90kJ endothermic 5,146 kJ heat

As shown in Table 1, the use of gaseous oxygen may be a method for increasing the temperature of the molten iron according to the exothermic reaction, and the use of solid oxygen may be a method for increasing the reaction efficiency. Therefore, in order to increase the reaction efficiency by using solid oxygen in the talline reaction, it may be necessary to increase the temperature of the molten iron by using gaseous oxygen in the degassing reaction. In addition, when the ratio of gaseous oxygen increases by 10% under the assumption that the weight ratio of gaseous oxygen to solid oxygen is 50:50 and the solid oxygen is decreased by 10%, the calorific value per 1 kg of silicon is about 560 kcal, Is 210 kcal / ton. ° C. Therefore, it can be calculated that the molten iron temperature of about 100 tons can be increased by about 0.026 ° C. per 1 kg of silicon. In other words, if about 0.25% of silicon remains in the molten iron, concentrating the gaseous oxygen at 100% of the gaseous acid consumption will result in an additional molten temperature rise of about 32.5 ° C Effect can be obtained. Through this temperature effect, it is possible to secure a margin for concentration of solid oxygen favorable in terms of efficiency in the talline reaction. That is, when the ratio of the solid oxygen to the gaseous oxygen is variably applied, it is possible to maximize the thermal energy of the degeneration reaction and maximize the efficiency of the talline reaction during the talline process.

Hereinafter, an example of the present invention will be described in order to confirm the effect of the present invention.

Implementation The construction according to one aspect of the present invention was applied to a talline process of a preliminary treatment facility of an open ladle charter line. The initial molten condition of the talline process, such as the temperature of the molten iron and the concentration of silicon (Si) after the degassing reaction, was at the same level as described below, and the gaseous oxygen: solid acid consumption during the talline process was 90 to 100 % By weight of gaseous oxygen, and the weight of oxygen required for talline in the latter half was 70 to 80% based on solid oxygen. The comparative example fixed the gas: solid acid consumption of the talline operation at about 50:50 level in the conventional manner. Conditions for the experiment are shown in Table 2 below.

Comparative Example Example Molybdenum temperature after Tallinn 1300 to 1350 degrees Silicon concentration after talline 0.1 to 0.3% Gas: solid acid consumption 40%: 60% to 60%: 40%
fixing Second half of first half
100%: 0% to 90%: 10% to 20%: 80% to 30%: 70%
(Oxygen required for degassing) (oxygen needed for talline) *

* The total amount of solid oxygen to be used does not exceed the amount used for gas oxygen: solid acid consumption 50:50

The results of the talline treatment of the comparative examples and the examples are compared in Table 3 below. As a result, the talline ratio (= concentration before phosphorus treatment - phosphorus concentration after talline treatment / phosphorus concentration before talline treatment × 100) was almost equal within the error range. However, when the composition of the present invention was applied in terms of the heating rate (= the molten iron temperature after the treatment - the molten iron temperature before the treatment), the effect of heating the molten iron temperature of 40 ° C or more was confirmed.

Comparative Example Example Number of processing 16 times 11 times Tallinn Rate 91.2% 88.9% Processing time 71 minutes 75 minutes Heating rate 25.8 DEG C 69.4 DEG C

To better understand the effect, each mean was statistically compared using t-test. The results are shown in Figs. 3 to 5.

Referring to FIG. 3 and FIG. 4, it can be seen that there is no significant difference in the error range between the talline ratio and the treatment time. This can be presumed to be a result of increasing the reaction efficiency by increasing the input amount of solid oxygen in the second kneading step 300. Referring to FIG. 5, the heating effect of the molten iron can be seen at a glance. It can be seen that the heating effect of 40 ° C or higher can be seen on average, which is a result of a large amount of gaseous oxygen prevailing in the exothermic reaction in the first kneading step (200).

100: Temperature measurement and silicon content measurement step
200: first spinning stage 300: second spinning stage
400: Finishing Stage a: Starting point of Tallinn Sewing
b: Starting point of the second smelting step
c: second smelting start point according to another embodiment
d: End point of second smelting step

Claims (4)

Measuring the initial temperature of the molten iron and the silicon content;
A first blowing step in which the weight ratio of the gaseous oxygen fed into the talline blowing furnace in the talline blowing process is greater than the weight ratio of the injected solid oxygen;
A second tinning step in which the weight ratio of the gaseous oxygen introduced is smaller than the weight ratio of the solid oxygen fed in the talline recycling process; And
And finishing the talline refining process when the heating rate of the charcoal line and the content of silicon contained in the charcoal line all reach the target value. The method according to claim 1,
The weight ratio of gaseous oxygen to solid oxygen in the first kneading step is 90:10 to 100: 0,
Wherein the weight ratio of gaseous oxygen to solid oxygen in the second crying step is 20:80 to 30:70. The method according to claim 1,
The first and the second curing steps are continuously performed,
Wherein the rate of silicon reduction of the molten iron at the boundary of the first and second stages is 0.1 to 0.4 times the silicon reduction rate of the molten iron at the beginning of the first stage. The method according to claim 1,
The target value indicates that the heating rate of the molten iron is the difference between the temperature and the initial temperature after the last stage of the talline blasting,
Wherein the heating rate is 55 to 80 DEG C, and the content of silicon is 0.1 to 0.3 wt% with respect to the total charcoal.

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