JP6223217B2 - Desulfurization method - Google Patents

Description

  The present invention relates to a desulfurization method in which hot metal and a cold iron source are charged into a hot metal transport container such as a hot metal ladle or a kneading car, and desulfurization is performed while a desulfurizing agent is added.

  In the iron making process, the hot metal discharged from the blast furnace is decarburized in the converter to produce steel, so the hot metal is transported from the blast furnace to the steel plant where the converter is located in a refractory container such as a kneading car or a pan (hot metal ladle). It is common to do. The transport flow is as follows: first, the hot metal is received in a pan-type container in the blast furnace cast floor, then transported to the steelmaking factory as it is, and the hot metal is charged into the converter, and second, in the blast furnace cast floor. A common method is to receive hot metal with a kneading car, transport it to a steelmaking plant, transfer the hot metal to a pot-shaped container to charge the converter, and then charge the hot metal into the converter from there. is there. In recent years, hot metal pretreatment such as desulfurization has been frequently performed even in hot metal transfer containers such as pans and kneading vehicles in order to cope with cost reduction and stricter quality requirements (for example, patents) (See Reference 1, etc.)

By the way, when receiving hot metal in a hot metal container such as a pan-shaped container or a kneading car, an operation is carried out to reduce the hot metal cost as much as possible by using an inexpensive cold iron source such as scrap as the iron source. It has been broken.
For example, in Patent Document 2, the hot metal in a hot metal ladle is discharged into a receiving container, and a cold iron source is placed in the bottom of the hot metal ladle before the hot metal is charged into an empty hot metal ladle. Then, a cold iron source charging method for charging hot metal into the hot metal ladle is disclosed. In the cold iron source charging method of Patent Document 2, the weight of the cold iron source placed in the hot metal ladle is appropriate, and heat loss due to the cold iron source can be reduced to prevent adverse effects on the operation. .

  Also in Patent Document 3, hot metal discharged from a blast furnace is received in a hot metal holding and conveying container in which a cold iron source is placed, and this hot metal is subjected to desulfurization treatment using a mechanical stirring desulfurization apparatus. Technology is disclosed.

JP 2004-300455 A JP 2007-113055 A JP 2006-219695 A

  By the way, the cold iron source mentioned above is supplied in order to increase the amount of hot metal and reduce the hot metal cost. For this reason, it is desirable that the amount of cold iron source put into the hot metal transfer container is large. On the other hand, if the amount of cold iron source put into the hot metal transfer container becomes too large, the heat loss due to the input of the cold iron source increases, Adhering the bullion to the transport container has adverse effects such as a reduction in the amount of hot metal transport and a decrease in productivity due to the bullion removal work.

  Furthermore, when the above-described desulfurization treatment or the like is performed in the hot metal transport container, if the temperature of the hot metal becomes too low due to the introduction of the cold iron source, the reaction efficiency of the desulfurization reaction may deteriorate and the desulfurization ability may also decrease. There is sex. Since the desulfurization reaction generally proceeds as the temperature rises, it is preferable to add as much cold iron source as possible within a range in which the desulfurization ability is not greatly reduced when the desulfurization treatment is performed in the hot metal transfer container.

However, the techniques of Patent Document 1 to Patent Document 3 described above do not take into account the decrease in desulfurization ability due to the introduction of a cold iron source. Even if the techniques of these documents are adopted, the amount of hot metal is reduced by the introduction of a cold iron source. It is difficult to ensure high desulfurization ability in the desulfurization treatment in the increased hot metal transfer container.
The present invention has been made in view of the above-described problems, and a desulfurization method capable of ensuring a good desulfurization ability while utilizing an inexpensive cold iron source when desulfurization is performed in a hot metal transfer container. The purpose is to provide.

In order to solve the above problems, the desulfurization method of the present invention takes the following technical means.
That is, in the desulfurization method of the present invention, when desulfurization is performed while introducing a desulfurizing agent from the outside into a hot metal transport container in which only hot metal and a cold iron source are charged, the input amount of the desulfurizing agent to be charged into the hot metal transport container W (kg / t), the amount of cold iron source charged into the hot metal transport container is m '(kg / t), the hot metal temperature before desulfurization treatment is T (° C), and the sulfur concentration before and after the desulfurization treatment When the difference is ΔS (mass%), the desulfurizing agent input amount W is set so as to satisfy the formula (1).

  According to the desulfurization method of the present invention, it is possible to ensure good desulfurization ability while utilizing an inexpensive cold iron source when desulfurization is performed in a hot metal transfer container.

It is a mimetic diagram imitating the flow from the blast furnace discharge to the primary refining process. It is the figure which put together the relationship between the difference between the input value of the desulfurization agent and the input amount (W) of the desulfurization agent obtained by the equation (1), and the sulfur concentration of the hot metal after the desulfurization treatment. It is the figure which showed each process of the desulfurization method.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically showing the smelting process of the hot metal discharged from the blast furnace 1.
As shown in FIG. 1, the hot metal discharged from the blast furnace 1 is received by the kneading vehicle 3 and then transported to the steelmaking factory where it is discharged to the hot metal ladle 5. The hot metal ladle 5 is moved to the removal position by a crane, and after removing the blast furnace slag existing immediately above the hot metal, it is carried to the front of the converter by the crane, and the hot metal in the ladle is charged into the converter. After the hot metal charging is completed, the empty hot metal ladle 5 is returned to the payout position again by the crane, and the hot metal of the next charge is discharged from the kneading vehicle 3.

  In such a smelting process, desulfurization by mechanical stirring may be carried out in the hot metal transport container 2 (hereinafter, the one including both the kneading car 3 and the hot metal ladle 5 is referred to as the hot metal transport container 2). In this embodiment, a desulfurization agent (desulfurization flux) is added to the hot metal ladle 5 after blast furnace slag removal, and the desulfurization reaction is advanced by mechanical stirring. And after removing desulfurization slag again in a removal position, the hot metal after desulfurization is discharged to a converter.

  In recent years, there has been an increasing demand for increasing the amount of crude steel and reducing refining costs. Instead of or in addition to hot metal discharged from the blast furnace, inexpensive iron sources such as scrap The use of is being considered. As one of the methods for this purpose, iron sources (cold iron sources) such as cold iron and scrap are put into the hot metal transport container 2, that is, the kneading wheel 3 and the hot metal ladle 5, and these cold iron sources 6 together with the hot metal. Operations to increase the amount of hot metal by melting

That is, as shown in FIG. 3, the desulfurization process in the hot metal ladle 5 (hot metal transfer container 2) of this embodiment has four steps.
The first step that constitutes the desulfurization process is “to load the hot metal into an empty hot metal transfer container”. In the example of FIG. 3, a hot metal ladle 5 is used as the hot metal transport container 2, and the hot metal is charged into the hot metal ladle 5 from the kneading wheel 3, but the blast furnace 1 is used as the hot metal transport container 2. The hot metal may be charged from 1 to the chaotic wheel 3. The hot metal transfer container 2 is charged with a weight M (t) of hot metal having a temperature of T _pig (° C.), and the hot metal contains sulfur at a concentration of S _pig (mass%).

The second step constituting the desulfurization process is “to put a cold iron source into the hot metal in the hot metal transport container”. That is, in the second step, the temperature in which the molten iron in the hot metal transfer container 2 charged in the first step is contained at a concentration of S _c (mass%) is T _c (° C.). The iron source 6 is charged by weight m (kg).
In the third step of the desulfurization process, the desulfurizing agent 7 is added to the hot metal transport container 2 by W (kg / t), and the refractory impeller 8 is immersed in the hot metal of the hot metal transport container 2 to The desulfurization reaction is promoted while forcibly stirring. If it does in this way, the sulfur in hot metal will transfer to a desulfurization agent in the 3rd process, and desulfurization slag will be formed, and it will obtain "hot metal from which sulfur content was removed" by removing the formed desulfurization slag. Can do. The molten iron (hot metal) increased in weight to M + m / 1000 (t) by melting the cold iron source 6 is accommodated in the molten iron transport container 2 in the third step. Moreover, the temperature of the molten metal at this time is lowered to the temperature T (° C.) due to the temperature rise and dissolution of the cold iron source, and the concentration of sulfur is S (mass%).

The fourth step constituting the desulfurization treatment is “to obtain a desulfurized hot metal”. In the fourth step, the desulfurization reaction in the third step is sufficiently advanced, and the sulfur content in the molten metal is removed as desulfurized slag, and the concentration of the sulfur content in the molten metal is reduced to a desired regulation value or less. Note that the molten metal in the hot metal transfer container 2 in the fourth step has a temperature of T _f (° C.) and a sulfur concentration of S _f (mass%).

  In the operation as described above, if the temperature of the hot metal in the hot metal transfer container 2 becomes too low due to the introduction of the cold iron source 6, the reaction efficiency of the desulfurization reaction is deteriorated and the desulfurization ability is lowered, and desulfurization is not performed. It may become sufficient, or it may be necessary to supplementary desulfurization in other processes, which may impair the productivity of crude steel. For this reason, it is necessary to set a lower limit (minimum required amount) for the amount of desulfurization agent 7 so that the desulfurization ability does not greatly decrease even when the cold iron source 6 is charged.

Therefore, in the present invention, the input amount of the desulfurizing agent 7 (lower limit value of the input amount) is determined as follows.
That is, the amount of desulfurization agent 7 charged into the hot metal transport container 2 is W (kg / t), and the amount of cold iron source 6 charged into the hot metal transport container 2 is m ′ (kg / t). Further, the hot metal temperature before the desulfurization treatment is T (° C.), and the difference in sulfur concentration before and after the desulfurization treatment is ΔS (mass%). In addition, the input amount W of the desulfurizing agent 7 is set in the desulfurization method of the present invention so that these parameters (W, m ′, T, ΔS) and the input amount W of the desulfurizing agent 7 satisfy the formula (1). doing.

The right side of the formula (1) is the lower limit of the input amount of the desulfurizing agent 7, and the desulfurization treatment is performed without reducing the desulfurization efficiency by introducing the desulfurizing agent 7 so as to be equal to or higher than the lower limit value of the input amount. It becomes possible to do.
In addition, the following values are used for each parameter used in Equation (1).
First, the input m ′ (kg / t) of the cold iron source 6 which is the first parameter is m (kg) of the input amount of the cold iron source 6 (total input amount), and before the cold iron source 6 is supplied. When the amount of hot metal (the amount of hot metal immediately after being charged into the hot metal transfer container 2) is M (t), the relationship is derived as shown in the equation (2).

An upper limit value is set for the total amount m (kg) of the cold iron source 6 so that the hot metal temperature after the charging does not decrease too much. The total input amount (upper limit) m (kg) of the cold iron source 6 is determined by the temperature T _c (° C.) of the hot metal before the supply of the cold iron source 6 and the cold iron source as shown in the equation (3). 6 of the temperature T _pig (° C.) hot metal temperature T '(° C.) after Hiyatetsu source turned indicated with like is defined as a value such that 1200 ° C. or higher.

Further, the hot metal temperature T (° C.) before the desulfurization treatment, which is the second parameter, is indicated as the hot metal temperature immediately after being charged into the hot metal transfer container 2 and is measured using an existing temperature sensor or the like. . When the hot metal temperature T (° C.) before the desulfurization treatment is 1165 (° C.) or less, the hot metal may be solidified, and the hot metal temperature T is controlled to be higher than 1165 (° C.).
Further, the sulfur parameter difference ΔS (mass%) before and after the desulfurization treatment, which is the third parameter, is obtained by subtracting the sulfur concentration of the hot metal after desulfurization from the sulfur concentration of the hot metal before desulfurization. Sulfur concentration [S] _pig (mass%) of hot metal before supplying the source, sulfur concentration [S] _c (mass%) of the cold iron source 6 input, sulfur concentration [S] _f ( (Mass%) is expressed as in equation (4).

It can be considered that the following relationship is established between the three parameters described above and the input amount W (kg / t) of the desulfurizing agent 7.
That is, when considering the case where desulfurization is performed while the cold iron source 6 is introduced, if the hot metal temperature before the desulfurization treatment is low, it is considered that the desulfurization reaction does not proceed easily. If the hot metal temperature is high, the desulfurization reaction proceeds. It will be easier. Further, since the hot metal temperature decreases as the amount of the cold iron source 6 is increased, the desulfurization reaction should be difficult to proceed as in the case where the hot metal temperature is low. Furthermore, when the input amount of the cold iron source 6 is reduced, the temperature of the hot metal should be increased and the desulfurization reaction should proceed easily.

On the other hand, if the cold iron source 6 or hot metal contains a large amount of sulfur, it is necessary to increase the desulfurization capacity by adding a large amount of the desulfurizing agent 7, and the cold iron source 6 or hot metal contains too much sulfur. If not, it is not necessary to increase the desulfurization capacity, and it is not necessary to add a large amount of the desulfurizing agent 7.
Based on this concept, the present inventors have introduced the amount m ′ (kg / t) of the cold iron source 6 to be fed into the hot metal transport container 2, the hot metal temperature T (° C.) before the desulfurization treatment, and before and after the desulfurization treatment. The relationship between these parameters (m ′, T, ΔS) and the input amount W (kg / t) of the desulfurizing agent 7 was summarized by various experiments and the like. As a result, when the desulfurization agent 7 is charged into the molten iron transport container 2 such as the kneading wheel 3 or the hot metal ladle 5, the molten iron after the desulfurization treatment can be obtained by satisfying the formula (1). It has been found that the sulfur concentration inside can be made 0.0030% by mass or less.

  If the sulfur concentration can be reduced to 0.0030% by mass or less in this way, the sulfur concentration in the steel will be within the standard for operation, and high-quality steel can be produced. If the above measures are not taken at all, the sulfur concentration exceeds the standard value of 0.0030% by mass, making it difficult to refining steel from which sulfur has been sufficiently removed, or adding desulfurization treatment in a separate process. Therefore, there is a possibility of impairing the productivity of steel.

  Table 1 summarizes the examples in which the operation was performed by the method of introducing the desulfurizing agent 7 of the present invention and the comparative examples in which the operation was performed by a method different from the present invention.

In the examples and comparative examples, the cold iron source 6 was put into the hot metal ladle 5 which is one of the hot metal transport containers 2, and the “sulfur concentration after desulfurization treatment” and the like were evaluated. In addition, the present inventors have confirmed that the same result can be obtained even if the cold iron source 6 is introduced into the hot metal transport container 2 such as the kneading vehicle 3 instead of the hot metal ladle 5.
Examples and comparative examples are as follows. First, an empty hot metal ladle 5 was melted in an induction melting furnace in an amount of 300 kg.
The pig iron was charged and heated and kept at a predetermined temperature. Then, the cold iron source 6 was thrown into the hot metal of this hot metal ladle 5.

Three types of “scrap”, “cold iron”, and “iron grain” were used as the cold iron source 6 put into the hot metal ladle 5. These cold iron sources 6 have a concentration of 0 to 0.003 (mass%) for "scrap", 0.025 to 0.03 (mass%) for "cold iron", and 0.07 (mass%) for "iron grains". And it contains sulfur.
A desulfurizing agent 7 was further added to the hot metal ladle 5 into which the above-described three types of cold iron sources 6 were put. The added desulfurization agent 7 is a CaO-based desulfurization flux containing CaO as a main component and containing 3 to 15% by mass of Al. The desulfurizing agent 7 is added to the hot metal in various amounts, and then the refractory impeller 8 is immersed in the hot metal, and the impeller 8 is rotated at 500 rpm to desulfurize the hot metal (mechanical stirring type). Desulfurization treatment) was performed for 15 minutes.

The amount of the desulfurizing agent 7 described above is calculated based on the calculated value of the “lower limit value of the input amount” calculated according to the equation (1). The amount ranges from large to small. The hot metal thus desulfurized was sampled, and the sulfur concentration was measured for each hot metal.
In the experimental examples of “No. 1” to “No. 6” and “No. 15” in Table 1, “scrap” is used as the cold iron source 6, and “cool iron source input amount m”. Is changed in the range of 3 kg to 15 kg. Looking at “Results—Lower Limit” in Table 1, the calculation results for all of these experimental examples are “Positive”, and “Desulfurizing agent amount (actual)” is “Desulfurizing agent amount (lower limit)”. And both satisfy the relationship of the formula (1).

Next, looking at the “sulfur concentration after treatment” in Table 1, all of the experimental examples of “No. 1” to “No. 6” and “No. 15” are standard values of sulfur concentration of 0. It is smaller than 0030 mass%. In other words, in the experimental examples “No. 1” to “No. 6” and “No. 15”, the sulfur concentration after the desulfurization treatment all satisfies the standard, and the sulfur content is sufficiently desulfurized from the hot metal. I understand that.
However, the experimental examples “No. 7” to “No. 14” in Table 1 also use “scrap” as the cold iron source 6, but the result of “result-lower limit” is “negative”. Therefore, the “desulfurizing agent amount (result)” is smaller than the “desulfurizing agent amount (lower limit)”. Therefore, unlike the experimental example described above, the experimental examples “No. 7” to “No. 14” do not satisfy the relationship of the formula (1).

Next, looking at the “sulfur concentration after treatment” in Table 1, all of the experimental examples “No. 7” to “No. 14” are larger than the standard value of sulfur concentration of 0.0030% by mass. ing. Therefore, in the experimental examples of “No. 7” to “No. 14”, the sulfur concentration after the desulfurization treatment does not satisfy the standard, and the sulfur content is not sufficiently desulfurized from the hot metal. Recognize.
In addition, although the experiment example mentioned above was a case where the cold iron source 6 was "scrap", the experiment example of "No.16"-"No.30" whose cold iron source 6 is "cold iron", The same tendency is also obtained in the experimental examples “No. 31” to “No. 45” in which the cold iron source 6 is “iron particles”. Equation (1) is derived by regression analysis of the data in the above-described embodiment.

The tendency as described above is more clearly shown by collectively showing the relationship of the sulfur concentration in the hot metal after the desulfurization treatment with respect to the “result-lower limit” of the sulfur concentration.
FIG. 2 summarizes the above-described examples and comparative examples. As shown in FIG. 2, when the value obtained by subtracting the lower limit value (the right side of the formula (1)) from the actual value of the sulfur concentration is 0 or more, that is, the input amount W ( kg / t), the amount m ′ (kg / t) of the cold iron source 6 charged into the hot metal transfer container 2, the hot metal temperature T (° C.) before the desulfurization process, and the sulfur concentration difference ΔS (mass%) before and after the desulfurization process. ) Satisfies the formula (1), it can be seen that the sulfur concentration after the desulfurization treatment can surely be reduced to the standard value (0.0030% by mass) or less.

As described above, when desulfurizing while introducing the desulfurizing agent 7 in the hot metal ladle 5 in which the cold iron source 6 is charged, the desulfurizing agent 7 is charged so as to satisfy the formula (1). It is possible to make use of an inexpensive cold iron source 6 while securing the above.
It should be noted that matters not explicitly disclosed in the embodiment disclosed this time, such as operating conditions and operating conditions, various parameters, dimensions, weights, volumes, and the like of a component, deviate from the range normally practiced by those skilled in the art. However, matters that can be easily assumed by those skilled in the art are employed.

DESCRIPTION OF SYMBOLS 1 Blast furnace 2 Hot metal conveyance container 3 Chaotic wheel 5 Hot metal ladle 6 Cold iron source 7 Desulfurization agent 8 Impeller

Claims (1)

When performing desulfurization while introducing a desulfurization agent from the outside into a hot metal transport container in which only hot metal and cold iron source are charged,
The amount of desulfurization agent charged to the hot metal transfer container W (kg / t), the amount of cold iron source input to the hot metal transfer container m ′ (kg / t), and the hot metal temperature before desulfurization treatment T (° C.), and when the difference in sulfur concentration before and after the desulfurization treatment is ΔS (mass%), the desulfurizing agent input amount W is set so as to satisfy the formula (1). .