JP5037290B2 - Hot metal dephosphorization method - Google Patents

Description

  The present invention relates to a hot metal dephosphorization method in which, in the hot metal preliminary treatment step, an oxygen gas jet is blown from the top blowing lance onto the surface of the hot metal in the converter to remove phosphorus in the hot metal.

  A method for dephosphorizing hot metal to make calcium phosphate by spraying an oxygen gas jet from the top blowing lance onto the hot metal surface to convert phosphorus in the hot metal into phosphoric acid and reacting with CaO components such as quicklime is widely known in the industry. ing. This dephosphorization method using an upper blowing lance has a problem that a large amount of iron oxide is scattered as fume or dust because the molten iron is stirred by the collision energy of the oxygen gas jet against the bath surface. There is also a problem that it takes a long time for the dephosphorization treatment.

  Therefore, for example, Japanese Patent Application Laid-Open No. 2001-11524, which is Patent Document 1, uses an upper blowing lance in which two types of lance holes having different nozzle angles and diameters are formed at the tip, and an oxygen gas jet blown from these lance holes. A dephosphorization method is widely disclosed in which is widely dispersed on the surface of the hot metal bath. It has been described that the collision energy of the oxygen gas jet against the bath surface can be reduced by using the upper blow lance having such two types of lance holes.

  However, even if the top blowing lance of Patent Document 1 is used, oxygen gas jets intensively collide with a specific place on the surface of the hot metal to form a hot spot (hot spot), and the surrounding slag is in a molten state. For this reason, the oxygen gas jet directly enters the hot metal while forming a cavity (concave) on the surface of the hot metal, and oxidizes iron to generate a large amount of fumes and dust. In addition, the reaction between oxygen and phosphorus in the hot metal proceeds only around the hot spot, and the other parts of the slag do not melt, so the rate of dephosphorization is slow, and dephosphorization requires a long time and a large amount of oxygen. It becomes. Thus, the hot metal dephosphorization method using a conventional top lance has a problem that a large amount of dust is generated and a long time is required.

  Although not related to the dephosphorization method, Japanese Patent Laid-Open No. 10-102122, which is Patent Document 2, discloses blowing while rotating an upper blowing lance having two types of lance holes with different nozzle angles at the tip. How to do is described. In this Patent Document 2, the oxygen gas jet from the inner nozzle collides with the surface of the molten steel, and dust generated by forming a cavity is struck back into the molten steel by the oxygen gas jet from the outer nozzle, It is described that the amount of dust generation is suppressed.

However, according to the results confirmed by the present inventors through tests, the effect of suppressing the amount of dust generated by the method of Patent Document 2 was not recognized. The method of Patent Document 2 relates to blowing for the purpose of decarburization, and does not contribute to the solution of the problem that it takes a long time for dephosphorization.
JP 2001-11524 A JP-A-10-102112

  Accordingly, the main object of the present invention is to solve the above-mentioned problems of the prior art, and to perform dephosphorization of the hot metal in the converter in the hot metal pretreatment process quickly without generating a large amount of dust. A dephosphorization method is provided. Another object of the present invention is to provide a hot metal dephosphorization method that can quickly remove hot metal in a converter while reducing the amount of auxiliary materials such as quicklime.

  The present invention, which has been made to solve the above-mentioned problems of the present invention, is a dephosphorization method for hot metal in which an oxygen gas jet is blown from the top blowing lance onto the hot metal surface in the converter. While rotating an upper blowing lance with more than one type of lance around its vertical axis, an oxygen gas jet is blown at a flow rate that does not penetrate the slag layer on the hot metal surface, and dephosphorization is performed through the slag layer. It is characterized by this.

  Furthermore, in the present invention, it is preferable to use an upper blowing lance in which the nozzle angles of the respective lance holes are all different angles. Moreover, in this invention, it is preferable that the sum of the area of the concentric ring which the oxygen gas jet sprayed from each rotating lance hole draws on the surface of a slag layer is 50% or more of the total surface area of a slag layer. Moreover, in this invention, it is preferable that the rotational speed of an upper blowing lance shall be 5-15 rpm.

  Furthermore, in this invention, it is preferable to introduce | transduce a quick lime powder as a CaO source in hot metal, and it is also preferable to insert a decarburizer with a quick lime powder as a CaO source in hot metal.

  According to the hot metal dephosphorization method of the present invention, the slag layer on the hot metal surface is rotated while rotating an upper blowing lance having three or more types of lance holes with different nozzle angles at the tip thereof around its vertical axis. Oxygen gas jet is blown at a flow rate that does not penetrate through, and oxygen is brought into contact with the hot metal through the slag layer to perform dephosphorization. As a result, the oxygen gas jet does not penetrate through the slag layer to form a cavity on the hot metal surface, and the amount of dust and fumes generated can be reduced as compared with the conventional case.

  In addition, the fire point is not fixed at a specific location as in the conventional method, but an oxygen gas jet is sprayed in a ring shape on the entire slag layer, and the entire slag layer is rapidly melted. For this reason, as shown in the data of the examples described later, oxygen quickly spreads over the entire surface of the hot metal, and dephosphorization proceeds in a short time. Although oxygen is ionized and penetrates the slag layer, dephosphorization through the slag layer makes it easier for oxygen to diffuse to the entire molten steel surface than by blowing an oxygen gas jet directly on the molten steel surface. Speed can be improved.

  As in claim 2, if an upper blowing lance with different nozzle angles for each lance hole is used, the oxygen gas jet blown from each nozzle is dispersed in a concentric circle with different radii on the surface of the hot metal, The above effects can be enhanced. In this case, the sum of the areas of concentric rings drawn on the surface of the slag layer by the oxygen gas jet blown from each lance hole as in claim 3 is 50% or more of the total surface area of the slag layer. If it is, it is more preferable.

  Further, as described in claim 4, the effect described above can be enhanced by setting the rotational speed of the top blowing lance to 5 to 15 rpm. This is because if the rotation speed is slower than 5 rpm, it becomes difficult to quickly melt the entire slag layer, and even if the rotation speed is faster than 15 rpm, an improvement in the effect is not recognized.

  Further, as described in claim 5, when quick lime powder is charged as a CaO source in the hot metal, the reaction between phosphoric acid and the CaO component is carried out quickly, so that the dephosphorization rate can be improved. If decarburized soot is introduced into the hot metal along with the powder of quick lime as a CaO source, the decarburized soot can be recycled, reducing the amount of auxiliary materials used, and reducing costs. Become.

The preferred embodiments of the present invention are shown below.
In FIG. 1, 1 is a converter for performing hot metal preliminary treatment, and 2 is an upper blowing lance inserted into the center of the converter from above. The converter 1 contains hot metal for hot metal preliminary treatment, and a slag layer S is formed on the upper surface thereof. As shown in FIGS. 2 and 3, at least three lance holes 3 are formed at the tip of the upper blowing lance 2. Each lance hole 3 has a nozzle shape for blowing out an oxygen gas jet. For at least three lance holes 3, each nozzle angle θ (angle between the axis of the lance hole and the central axis of the upper lance 2) is Everything is different.

  In this embodiment, there are eight lance holes 3 arranged on the same circumference. The lance holes 3 exceeding three may have the same nozzle angle θ, but preferably the nozzle angles θ are all changed for all the lance holes 3. In this embodiment, the nozzle angles θ of the eight lance holes 3 are 16 °, 24 °, 20 °, 28 °, 18 °, 26 °, and 22 ° in order from the 12 o'clock position in FIG. 30 ° and is set in the range of 16 ° to 30 °. If the nozzle angle θ is smaller than this range, the oxygen gas jet concentrates at the center of the hot metal surface in the converter 1, which is not preferable. When the nozzle angle θ is larger than this range, the oxygen gas jet collides with the vicinity of the converter wall.

  As in this embodiment, the nozzle angles θ of the lance holes 3 are alternately changed so as to change the directions of the oxygen gas jets from the adjacent lance holes 3 so that the oxygen gas jets do not interfere with each other. It is preferable to do. However, these angles are merely examples, and it goes without saying that they can be changed in various ways.

  The upper blowing lance 2 ejects oxygen gas jets from the lance holes 3 while being continuously rotated around its vertical axis by an appropriate rotating mechanism 4. As a result, concentric rings R are formed on the surface of the slag layer S in the converter 1 as shown in FIG. The width is determined by the spread angle of the oxygen gas jet ejected from the lance hole 3 and the distance to the slag surface, and the position is determined by the nozzle angle θ of the lance hole 3 described above. By changing all the nozzle angles θ of the eight lance holes 3 as described above, eight rings R are formed.

  The ring R is a movement locus of a hot spot where the slag layer S melts at a high temperature due to the reaction with oxygen. If the rotation speed is set to about 5 to 15 rpm, the ring R becomes a continuous hot ring. This makes it possible to quickly melt the entire slag layer. However, if the rotation speed is slower than 5 rpm, it becomes difficult to melt the entire slag layer quickly, and even if it is rotated faster than 15 rpm, an improvement in the effect is not recognized, so about 5 to 15 rpm is preferable.

  In addition, it is preferable to determine the arrangement of the lance holes 3 so that the sum of the areas of a large number of rings R drawn on the surface of the slag layer S by the oxygen gas jet is 50% or more of the total surface area of the slag layer S.

  In the present invention, the oxygen gas jets are dispersed and blown out from such a large number of lance holes 3 to reduce the flow velocity and collision energy of each oxygen gas jet. And as shown to FIG. 5B, an oxygen gas jet is sprayed with the flow velocity which does not penetrate the slag layer S of the hot metal surface.

  Conventionally, as shown in FIG. 5A, the oxygen gas jet penetrates the slag layer S and forms a cavity on the hot metal surface, and a large amount of fumes and dust mainly composed of iron oxide are generated accordingly. . In contrast, in the present invention, the oxygen gas jet does not penetrate the slag layer S and reach the hot metal surface. Therefore, the generation amount of fume and dust can be reduced.

  Conventionally, dephosphorization is performed by directly contacting the oxygen gas jet with the molten iron. However, in the present invention, the oxygen gas jet is not directly contacted with the molten iron, and dephosphorization proceeds through the molten slag layer S. To do. That is, oxygen that reaches the slag layer S is ionized and passes through the slag layer S, and reacts with phosphorus in the hot metal. As described above, in the present invention, by dephosphorization reaction proceeding through the slag layer S, oxygen is dispersed inside the slag layer S, and the dephosphorization reaction can proceed in a wider area. The dephosphorization rate can be improved as shown in the example data.

  In addition, in the hot metal of the converter 1, a raw stone is inserted as a CaO source. However, quick lime powder may be charged. CaO reacts with phosphoric acid to become calcium phosphate and floats as slag. Quicklime is a substance with low thermal conductivity, but its reactivity is improved by pulverization. Quick lime may be supplied from the nozzle 5 at the bottom of the converter 1 or from above.

  Although the CaO source is essential for dephosphorization, it is preferable to reduce the amount of quicklime used as much as possible. For this reason, together with quicklime, recycled raw materials containing quicklime, for example, agglomerate cake, calcium aluminate, decarburized cake, etc., can be charged. This decarburized soot is slag generated in the process of decarburizing the hot metal after dephosphorization, and the phosphorus content is low and also contains an unreacted CaO component. For this reason, by using quick lime and decarburized soot together, the amount of quick lime used can be reduced and slag can be recycled.

  As shown in the following examples, according to the present invention, immediately after the start of the dephosphorization operation, the phosphorus concentration in the hot metal decreases rapidly, and the degassing can be carried out in a short time compared with the conventional method in which the top blowing lance 2 is not rotated. Phosphorus can be completed. Further, as shown in the following embodiments, the effect becomes more remarkable by increasing the types of nozzle angles of the lance hole 3.

  In order to confirm the effect of the present invention, a hot metal dephosphorization experiment was conducted using an actual machine. In the experiment, hot metal (1300 ° C.), secondary raw materials, and scrap of hot metal pretreatment conditions were charged into a converter for hot metal pretreatment, and blown while rotating the upper blowing lance shown in FIG. 2 at 10 rpm. In-furnace sampling was performed using a sub lance to confirm the phosphorus concentration in the metal, and the dephosphorization rate was compared with the case where the top blowing lance was not rotated. For comparison, the same experiment was performed using two types of nozzle angles (20 ° and 30 °) and eight lance holes.

The experimental conditions are as follows.
Input basicity: 1.8
Basicity adjustment auxiliary materials: quick lime and decarburized cocoon Distance between lance tip and hot water surface: 3.3m
Total acid speed of top blowing: 15000 Nm ³ / hr
Input P concentration: 0.060 to 0.090%
Input Si concentration: 0.20 to 0.30%

  Since the dephosphorization rate progresses exponentially with the effective oxygen amount (the amount of oxygen supplied in addition to the oxygen required for the desiliconization reaction), the logarithm of the phosphorus concentration in the metal with respect to the desiliconization oxygen unit Plotted to create the graph of FIG. In order to eliminate the difference due to the input P concentration, the plot was made by correcting the input P concentration to be 0.060%.

  In FIG. 6, the lance hole angle is displayed as “constant” for an upper blowing lance having eight lance holes with two different nozzle angles, and “various” is displayed in the figure. 2 is an upper blow lance provided with eight lance holes of eight types having different nozzle angles. In addition, the lance rotation is displayed when it is rotated at 10 rpm.

  As shown in the graph of FIG. 6, even in the case of two types of lance holes with different nozzle angles, when the top blowing lance is rotated, the phosphorus concentration in the same oxygen basic unit is lower than when not rotating. Although the dephosphorization rate was improved, it was confirmed that the decrease in the dephosphorization rate was particularly remarkable when the upper blowing lance having a large number of lance holes with different nozzle angles was rotated. The data in FIG. 6 is for the top blowing lance shown in FIG. 2 (eight lance holes). However, even if the nozzle angle of the lance hole is reduced to three different types, it is removed from the two types. It is estimated that the phosphorus rate is significantly improved.

It is sectional drawing which shows embodiment of this invention. It is sectional drawing of a lance front-end | tip part. It is a bottom view of a lance tip part. It is a top view which shows the blowing state of the oxygen gas jet to the surface of a slag layer. It is a schematic diagram of the approach state of the oxygen gas jet to the hot metal surface, A is the conventional method, B is the method of the present invention. It is a graph which shows the data of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Converter 2 Top blowing lance 3 Lance hole 4 Rotation mechanism 5 Nozzle

Claims (6)

  In a hot metal dephosphorization method in which an oxygen gas jet is blown from the top blowing lance onto the surface of the hot metal in the converter, an upper blowing lance having three or more types of lance holes with different nozzle angles at the tip is arranged with its vertical axis. A hot metal dephosphorization method characterized in that an oxygen gas jet is blown at a flow rate that does not penetrate the slag layer on the hot metal surface while rotating around the hot metal surface to cause dephosphorization through the slag layer.   2. The hot metal dephosphorization method according to claim 1, wherein an upper blowing lance having different nozzle angles for each lance hole is used.   The sum of the areas of concentric rings drawn on the surface of the slag layer by the oxygen gas jet sprayed from each rotating lance hole is 50% or more of the total surface area of the slag layer. Of dephosphorizing hot metal.   2. The hot metal dephosphorization method according to claim 1, wherein the rotation speed of the top blowing lance is 5 to 15 rpm.   2. The hot metal dephosphorization method according to claim 1, wherein quick lime powder is charged as a CaO source in the hot metal.   2. The hot metal dephosphorization method according to claim 1, wherein a decarburized iron is charged together with quicklime powder as a CaO source in the hot metal.

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