JPS6152212B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of decarburizing and refining hot metal whose Si, P, and S contents have been reduced in advance using a small freeboard reaction vessel. Generally, the reaction vessel in the oxygen steel refining process has a fairly large freeboard. For example, in the case of a converter, the depth of the molten metal when it is stationary is at most about 10 to 30% of the inner height, and most of the remaining part is freeboard that does not come into contact with the molten metal. This is caused by the rocking phenomenon of the molten metal caused by powerfully blowing oxygen gas at supersonic speed onto the molten metal surface, the slopping phenomenon of generated slag outside the furnace, and the scattering of fine iron particles outside the furnace (slopping). This is considered a necessary measure to prevent the phenomenon of spitting. Such an excessively large freeboard not only has the disadvantage of increasing the equipment weight of the reaction vessel and the amount of refractories used relative to the weight of hot metal being processed, but also reduces productivity by prolonging furnace construction and repair time. This will cause harm. In addition, the current converter steel manufacturing method uses a large amount of slag-forming agent in order to have the functions of decarburization, desiliconization, phosphorization, and desulfurization.
A huge amount of slag weighing 100 to 130 kg is generated incidentally. Problems with the current steel manufacturing method that involves such a large amount of slag include the following. (1) A large amount of slag promotes the slopping phenomenon, leading to a decrease in iron yield. In order to prevent slopping, an excessively large freeboard is required, which causes the above-mentioned disadvantages. (2) Decrease in iron yield due to increase in iron oxide contained in slag. (3) Decrease in thermal efficiency due to slag sensible heat and decrease in scrap content ratio. etc. The present invention provides a method for solving the above problems, and its features are as follows: 1. Hot metal whose Si, P, and S content has been reduced in advance is decarburized under conditions that satisfy the following three items. , a decarburization refining method in a small freeboard reaction vessel. (i) The static depth Lo of the charged molten metal satisfies the relationship Lo/Lt≧0.6 with respect to the internal height Lt of the reaction vessel. (ii) The penetration depth L of the oxygen jet into the molten metal is L/Lo
Satisfy the relationship ≦0.3. However, L=Lh・exp(−0.78h/Lh) Lh=63.0(kFo ₂ /nd) ^2/3 Lo: Rest depth of molten metal (mm) L= Molten metal penetration depth of oxygen jet (mm) h= Lance hot water surface spacing (mm) Fo ₂ : Oxygen flow rate (Nm ³ /Hr) n: Number of holes in the lance nozzle d: Diameter of the lance nozzle (mm) k: Correction coefficient based on the nozzle injection angle θ When n=1 1 When n≧2: 1.7 when θ=0 1.4 when θ=6° 1 when θ=10° (iii) A lance immersed in the molten metal or a breathable refractory or tuyeres installed below the reaction vessel, etc. Injecting gas into the molten metal and stirring the molten metal by the floating and expansion phenomenon of the gas. and 2. A decarburization refining method in a small freeboard reaction vessel according to claim 1, characterized in that a removable side wall is provided at the upper part of the reaction vessel. In order to overcome the aforementioned problems caused by slag, there is no need for a slag-forming agent.In other words, it is sufficient to use raw hot metal that has been subjected to P and S removal treatment, and Si is
0.20% or less (preferably trace), and P, S
are below the required standard component values. As a result, the amount of slag generated is significantly reduced and oxygen is blown in a state similar to that of bare hot water, so problems caused by slag such as slopping can be prevented. However, if oxygen is blown under conditions similar to those currently used in converters in conditions similar to those of bare hot water, the oxygen jet tends to scatter the hot metal upwards due to the absence of a slag layer, resulting in severe spitting and, on the contrary, This causes a decrease in retention. The oxygen blowing conditions currently used in converters are so-called hard blow conditions where L/Lo is between 0.7 and 1.0 for the purpose of decarburization blowing, and the oxygen blowing conditions are simply those of the oxygen supply function. In addition, it has the function of penetrating the slag layer and stirring the molten metal to increase reaction efficiency. Under such hard blowing conditions, the molten metal swings greatly and the amount of spitting increases, and as a result, the amount of hot metal to be processed relative to the internal volume of the reaction vessel must be reduced and the freeboard must be increased. To reduce rocking and spitting,
Soft blowing, which gently blows oxygen onto the surface of the molten metal, is effective. Soft blowing in current converter operations is usually carried out at L/Lo between 0.4 and 0.7 in order to increase the oxygen potential in the slag and promote dephosphorization, but the method of the present invention basically There is no such thing, and only decarburization is expected. In this sense, direct contact between oxygen and hot metal is easy, so the decarburization reaction is promoted even under ultra-soft blow conditions that would be unthinkable in normal converter operation, that is, under L/Lo of 0.3 or less. The freeboard height can also be reduced. L/Lo is usually lance level interval h and oxygen flow rate Fo ₂
controlled by The lower limit of h is limited by lance melting, and the upper limit is limited by the height that does not go outside the reaction vessel in order to ensure oxygen efficiency (the height of the side wall if there is a removable side wall), and within this range. selected. Fo ₂ is determined by the treatment time setting, but when it is necessary to flow a large amount of oxygen in a short period of time, a porous lance and/or multiple lances are used to disperse the oxygen jet. An effective method is to reduce the molten metal penetration depth L. In the conventional converter method, the oxygen jet has both the functions of supplying oxygen and stirring the molten metal, but in the method of the present invention, in order to suppress spitting, the functions are actively separated to perform only the former function.
If hot metal is not sufficiently stirred, an iron oxide layer will form and accumulate on the surface of the hot metal, which will not only reduce the blowing oxygen efficiency but also rapidly react with the carbon in the hot metal during blowing, producing a large amount of waste gas. At the same time, a phenomenon occurs in which the contents are blown up, and stable blowing cannot be expected. In order to prevent this phenomenon, when blowing is carried out under ultra-soft blowing conditions as in the method of the present invention, a lance immersed in the molten metal or an air-permeable refractory or tuyeres provided below the reaction vessel are used to blow gas into the molten metal. A necessary structural condition is to stir the molten metal by the floating and expansion phenomenon of the gas. By stirring, iron oxide is reduced by the carbon in the hot metal without being accumulated, and the decarburization reaction can be stably promoted. The decarburization refining method of the present invention will be explained below with reference to drawings and examples. FIG. 1 is a schematic diagram showing an example of the decarburization refining method according to the present invention, in which 1 is a reaction vessel, 2 is a molten metal, 3 is a lance for oxygen blowing, and 4 is an air-permeable refractory for blowing stirring gas. . Inner height of reaction vessel 1
The static depth Lo of the charged molten metal is Lo/
The relationship Lt≧0.6 is satisfied. The upper limit of Lo/Lt is limited to the extent that the swinging height of the molten metal during blowing does not exceed the freeboard height H. That is, if the maximum height of molten metal rocking due to blowing is Ls, then the range of Lo/Lt is 0.6≦Lo/Lt<1−Ls/Lt. (Even if Lo/Lt<0.6, the decarburization refining method according to the present invention
Of course, decarburization is possible, but the amount of molten metal processed is smaller than the current converter method compared to the scale of the reactor vessel equipment, and sufficient economic benefits cannot be enjoyed. ) A plurality of lances 3 for oxygen blowing and a plurality of breathable refractories 4 for blowing stirring gas may be provided as necessary. Other examples are shown in FIGS. 2 and 3. FIG. 2 shows an example in which two tuyeres 5 for blowing stirring gas are installed below the reaction vessel instead of the breathable refractory 4, and three lances 3 for blowing oxygen are used. FIG. 3 shows a case in which the stirring gas is blown in with an immersion lance 6, and also shows an example in which a removable side wall 7 is attached. Figure 4 shows the relationship between L/Lo, the amount of scattering outside the container, and the decarburization reaction rate.
A comparison is made with the conventional method using Lt) as a parameter. In the conventional method, Lo/Lt=0.2, and in the present invention, Lo/Lt=0.7. Therefore, in the present invention, the preferable tolerance limit in terms of iron yield is L/Lo≦
Although limited to the range of 0.3, even in such an ultra-soft blow region, the decarburization reaction rate can be maintained at a high level because oxygen and molten metal are in direct contact, and the small freeboard reaction can be maintained. Even in a container, the decarburization reaction can be promoted while suppressing spitting. Furthermore, when aiming to improve yield, detachable side walls can be installed to prevent spitting. Table 1 shows the decarburization blowing conditions and blowing results according to the present invention.

【table】

[Table] If the flow rate of the stirring gas is too low, the accumulation of iron oxide will progress and the content will blow up, so it is required to be at least 0.05 Nm ³ /min·t. As seen in the examples, according to the method of the present invention, decarburization blowing can be carried out stably and with a high yield without requiring an excessively large amount of freeboard, thereby reducing the construction and maintenance costs of the equipment. At the same time, the amount of auxiliary raw materials (quicklime, etc.) used is reduced, and manufacturing costs can be reduced. In addition, the amount of slag generated is significantly reduced, making the slag treatment equipment more compact.Also, since the amount of free oxygen during blow-up is lower than in the conventional method, the yield of ferroalloy is improved, which is an extremely useful effect industrially. can be expected.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are diagrams showing embodiments of the decarburization refining method according to the present invention, and Figure 4 is L/Lo.
FIG. 3 is a diagram comparing the relationship between the amount of scattering outside the container and the decarburization reaction rate with the conventional method using the hot metal charging rate (Lo/Lt) as a parameter. 1... Reaction vessel, 2... Molten metal, 3... Oxygen blowing lance, 4... Breathable refractory, 5... Tuyere, 6
...Immersion lance, 7...Removable side wall.

Claims (1)

[Claims] 1. A decarburization refining method in a small freeboard reaction vessel, characterized in that hot metal whose Si, P, and S content has been reduced in advance is decarburized under conditions that satisfy the following three items. (i) The static depth Lo of the charged molten metal satisfies the relationship Lo/Lt≧0.6 with respect to the internal height Lt of the reaction vessel. (ii) The penetration depth of the oxygen jet into the molten metal is L/Lo≦
Satisfy the relationship of 0.3. However, L=Lh・exp(−0.78h/Lh) Lh=63.0(kFo ₂ /nd) ^2/3 Lo: Rest depth of molten metal (mm) L= Molten metal penetration depth of oxygen jet (mm) h= Lance hot water surface spacing (mm) Fo ₂ : Oxygen flow rate (Nm ³ /Hr) n: Number of holes in the lance nozzle d: Diameter of the lance nozzle (mm) k: Correction coefficient based on the nozzle injection angle θ When n=1 1 When n≧2: 1.7 when θ=0 1.4 when θ=6° 1 when θ=10° (iii) A lance immersed in the molten metal or a breathable refractory or tuyeres installed below the reaction vessel, etc. Injecting gas into the molten metal and stirring the molten metal by the floating and expansion phenomenon of the gas. 2. The decarburization refining method in a small freeboard reaction vessel according to claim 1, characterized in that a removable side wall is provided at the upper part of the reaction vessel.