JPS6315325B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for carburizing, melting, and refining hot metal. The blast furnace-converter method, which currently dominates the iron refining process,
The amount of heat required for iron smelting and melting depends on the oxidation reaction heat of C, Si, etc. in the hot metal and the sensible heat of the hot metal itself, so the scrap digestion capacity is generally 20-30%, and 70%-80%. % of hot metal must be used as the main ingredient. In addition, the method of reducing and recovering iron by adding iron ore during converter refining is an extremely rational iron reduction method, but it absorbs a lot of heat, and in general converter refining, the
Currently, only iron ore weighing between 10Kg and 40Kg can be used. In this way, the converter refining method, which uses hot metal as the main raw material, cannot consume a large amount of scrap due to thermal problems, and the most rational iron ore reduction is carried out by adding a large amount of iron ore. things are impossible. In order to solve these difficulties, various methods have been proposed to improve the thermal margin of the converter by adding carbon materials (coke, coal), etc. as a heat source during converter refining. The method uses the thermal margin of the converter as the scrap consumption for the following reasons.
The improvement was only about 3 to 7% at most. (1) Carburizing substances such as coke and coal contain a large amount of ash, and in a single container like a converter, slag increases dramatically, and there is a limit to the amount of carburizing. (2) The decarburization reaction in general converter decarburization refining is mainly caused by C
+1/20 ₂ →CO, the calorific value is about 1/3 lower than the reaction of C+O ₂ →CO ₂ , and a large amount of carbon material must be added to the converter. In that case, in addition to the problem (1) naturally occurring, a large amount of high temperature
CO gas is generated as exhaust gas and takes away the heat inside the furnace, making this method unviable from an economical point of view. The present invention provides a method for carburizing, melting and refining hot metal, which achieves the reaction with the highest calorific value in decarburization refining using top-blown oxygen gas, and optimizes the thermal efficiency in the furnace. Furthermore, the present invention provides an efficient method for melting and refining input scrap iron and iron ore by adding a heat source to hot metal through carburization during refining using top-blown oxygen gas. The present invention will be explained in detail below. As a result of examining elemental technologies for improving thermal efficiency in carburization, decarburization, melting and refining using hot metal mainly using top-blown oxygen, we found that:
The following facts have become clear. The basis for improving thermal efficiency is that the carbon in the hot metal undergoes a C+O ₂ → CO ₂ reaction during oxygen refining of the hot metal.As a result of investigating the necessary conditions to achieve this, we found that oxygen refining with bottom blowing Oxygen blowing conditions and CO in exhaust gas at
As shown in Figure 2, the relationship between CO ₂ + CO is extremely strong with the hot spot area/bath surface area ratio and hot metal bath depth/hot metal bath inner diameter ratio; the larger the hot metal bath area ratio, the deeper the bath depth. The reaction C + O ₂ → CO ₂ occurs frequently, and when the fire spot area/bath surface area is around 0.5 and the bath depth/bath inner diameter is around 0.5,
It is clear that there is a critical point near 0.5. If the inner diameter of the hot metal bath is not circular, use the inner diameter equivalent to the circular area. The above hot spot area/bath surface area has a close relationship with the hot metal temperature during decarburization refining, which will be explained next. Here, the flash point area/bath surface area means, as shown in Figure 1, when oxygen gas is ejaculated, it is injected from the lance hole,
The area S geometrically projected onto the bath surface is the bath surface area.
Indicates the proportion of Ls. Next, the relationship between hot metal temperature and exhaust gas CO/CO ₂ +CO is as shown in Figure 3.
It is clear that the CO/CO ₂ +CO ratio decreases rapidly below 1500°C, and that there is a critical point at 1500°C.
The figure shows flashing point area/bath surface area = 0.65, slag amount 10Kg/
According to experiments, the hot metal temperature can be maintained at 0.3 or higher while keeping the hot spot area/bath surface area at 0.3 or higher.
A decrease in the CO/CO ₂ +CO ratio was confirmed when controlling the temperature below 1500°C. Furthermore, the relationship between the amount of slag in the furnace and CO/CO ₂ +CO in the exhaust gas is as shown in Figure 4. ₂ The relationship between +CO and slag amount is 15Kg/t.
It is clear that above this level, the value will rise rapidly. The spark spot area/bath surface area in the figure is 0.6. As a result of examining the above elemental conditions, in the carburization melting and refining method, the most efficient decarburization reaction using top-blown oxygen gas actively causes the reaction with the highest calorific value of C + O ₂ → CO ₂ , and the furnace The means of optimizing internal heat efficiency is the firing point area/bath area during oxygen gas decarburization refining>
0.5 and bath depth/bath inner diameter ≧0.5. Note that when the hot metal temperature is maintained below 1500℃, this value can be expanded to 0.3 respectively. Furthermore, according to the present invention, in addition to the hot spot area/bath surface area conditions, the hot metal temperature during oxygen gas decarburization refining is
It was confirmed that it is desirable to maintain the temperature at 1500°C or lower, and that it is most efficient when an elemental technology is added to control the amount of slag during oxygen gas decarburization refining to 15 kg/t or lower. Next, an application example of the carburization melting and refining method of the present invention will be explained. FIG. 5 shows the apparatus of the invention. In the figure, the carburization tank 10 has a slag hole 12, a bottom-blown stirring gas hole 14, a carburization agent injector 11, a scrap iron and iron ore input device 23, and a separation wall 13 at the boundary with the decarburization melting and refining tank 21. establish. The separation wall 13 separates the carburization tank 10 and the decarburization melting and refining tank 21 in the upper region of the hot metal, and forms a flow path for the molten metal in the bottom of the tank. The decarburization melting and refining tank 21 has an oxygen gas lance 22, a tapping hole 24, a bottom blowing stirring gas hole 25, and an electromagnetic stirring device 26 is provided near the conduction area of the separation wall. According to the present invention, after charging a small amount of hot metal into a melting and refining furnace consisting of two tanks (or leaving it in the furnace in advance), in the carburization tank, while blowing bottom-blown stirring gas, a carburizing agent is added to the top of the furnace. It is added to hot metal by charging at a more appropriate time or by injection method. When more than a certain amount of slag is generated, the slag is naturally drained from the slag drainage hole, or it is forcibly removed using a slag cleaner or the like. On the other hand, in the decarburization melting and refining tank, the hot metal bath depth (m)/
Continue decarburization refining while blowing top-blown oxygen and bottom-blowing gas to strengthen stirring so that the hot metal bath inner diameter (m) is maintained at 0.5 or more and the hot spot area/bath surface area≧0.50. Also, at least while carburization is being carried out in the carburization tank, oxidizing substances such as scrap or iron ore are added from above to prevent the hot metal temperature from exceeding 1500°C. If necessary, a refining agent such as lime or fluorite is added. According to experiments, the temperature of hot metal
When controlling below 1500℃, L/D and S/Ls
can be 0.3 or higher. After the necessary amount of carburization and melting, the hot metal can be poured out, or the decarburization and refining can be continued and the steel can be tapped when the required molten steel temperature and carbon content are reached. The separation wall between the decarburization melting and refining tank and the carburization tank is sufficient as long as the molten pig iron in the smelting tank and the carburization tank can mix with each other in the lower layer of the molten pig iron, and its main purpose is to separate the decarburization melting tank and the carburization tank. This prevents slag from the coal tank from flowing into the smelting tank. By doing the above, it became possible to digest a large amount of scrap with extremely high thermal efficiency, and it also became possible to reduce a large amount of oxides such as iron ore. FIG. 6 is an explanatory diagram of another example of application of the present invention. The carburization tank 10 and the decarburization melting and refining tank 21 are the same as those shown in FIG. A desulfurizing agent injection tank 32 is provided, and a bottom blowing stirring gas blowing hole 14-2 is provided. This example adds a desulfurization tank, but the desulfurization method is
It is possible to charge the desulfurizing agent upward and stir the gas from the bottom, or it is also possible to blow it in with an injection lance. As a method to prevent the slag from each reaction tank from entering the decarburization tank, in addition to separating the hot metal from each tank at the top in one container as described above, It is also possible to connect the containers by an electromagnetic force transfer method, a vacuum suction transfer method, etc., and transfer and mix the molten metal from each other. FIG. 7A shows a plan view of still another application example of the present invention. Decarburization melting and refining tank 21, carburization tank 10, desulfurization tank 3
This is a box-shaped three-tank separation type melting and refining furnace in which 1. 27 is a vacuum slag cleaner, and 19 is a hot metal transfer hole (FIG. 7B). That is, according to this example, in the first tank 21, oxygen gas is blown from the top using a lance 22, stirring gas is blown from the bottom, and iron ore charging device 21 is used to perform melting and refining. Crude molten steel is introduced into the second tank 10, coal powder is injected with the top blowing lance 11, and the generated slag is passed through the slag hole 1.
Discharge in 2. In the third tank 31, the desulfurization agent is returned to the first layer 21 after desulfurization using the injector 32, and continuous operation can be performed. FIG. 8 is a schematic diagram showing still another example of application of the present invention. In the figure, the carburization tank 10, the decarburization melting and refining tank 21, and the desulfurization tank 31 are connected to each other through a passage 36,
The molten metal is transferred by an electromagnetic transfer device 35. The slag off 12 is placed in the carburization tank 10, and the desulfurization (dephosphorization) tank 31
A slag-off 33 is provided in the molten steel, and molten steel is tapped from the decarburization melting and refining tank 21 into a ladle 27. Although the present invention has been described above with reference to an example in which the present invention is mainly applied to a separate continuous furnace, it does not depart from the scope of the present invention to operate with a single batch type furnace, unless it is contrary to the purpose of the present invention. As mentioned above, in carrying out carburization melting and refining of hot metal, the present invention provides a stirring gas bottom blowing hole in the bottom of the furnace, separates the upper layer region of the hot metal with a separation wall, and configures at least two tanks. By forming a coal tank and a decarburizing melting and refining tank, and adding a desulfurization tank as a third tank if necessary, a large amount of auxiliary raw materials such as iron ore and scrap iron can be processed in combination with coal addition during oxygen gas top-blowing refining. It makes charcoal melting and refining possible and has great industrial effects. Example 1 In a 180t oxygen top-blowing, Ar gas bottom-blowing combined refining furnace, the bath diameter was L3.2m, bath depth D3.2m (L/D=1.0, hereinafter referred to as L/D), and the oxygen was blown from the top-blowing lance. Spark spot area on the steel bath surface (total area of collision of oxygen gas against the steel bath surface ≒ N × (R + l・tanQ) ² × π N = number of lance nozzles R = lance hole radius l = lance height Q = nozzle throat Adjust the lance height so that the angle is 5.6m ² (flame area ratio 0.7), and as shown in Table 1, C +
By actively promoting the O ₂ → CO ₂ reaction, we were able to melt a large amount of scrap and refine steel.

[Table] Example 2 In a composite refining furnace with 200t oxygen top blowing and Ar gas bottom blowing, the bath diameter was 3.2 m and the bath depth was 3.2 m (L/D = 1.0). The flash point area is
The lance height was adjusted to ^5.6m2 , and iron ore was added to the furnace during oxygen refining so that the temperature in the steel bath was 1450℃ or less when the C% in the steel bath was 1% or more. As a result of refining, as shown in Table 2, C + O ₂ → CO ₂
By proactively carrying out this reaction, we were able to use a large amount of iron ore and carry out smelting with a high iron yield.

[Table] Example 3 After charging 50 tons of hot metal in the pear-shaped melting and refining furnace with two separated hot metal tanks shown in Figure 5, the bath diameter was 2.6 m and the bath depth was
While blowing coke powder with _N2 gas from the top onto the hot metal surface at a speed of 500 kg/min in the 1.3 m (L/D = 0.5) carburization tank side, a porous lance was used in the decarburization refining tank. Fire point area/bath surface area = 65%, acid passing rate
Blowing was carried out at a rate of 500Nm ³ /min, and 600Nm ³ /hour of Ar gas was blown into both tanks from the bottom of the furnace through a porous, small diameter nozzle (refractory) to maintain the slag in the decarburization tank below 10Kg/t-steel. . In addition, in order to prevent the hot metal temperature during carburization from exceeding 1400℃, scrap is added to the decarburization melting and refining tank at appropriate times according to the hot metal temperature during refining, and then decarburization is performed. As shown, it was possible to melt a large amount of scrap extremely efficiently and produce crude molten steel.

【table】

[Table] Example 4 In the box-type three-tank separated melting and refining furnace shown in Fig. 7, the first tank has a bath diameter of 2.0 m and a bath depth of 2.0 m (L/D =
1.0), oxygen gas is supplied from the top with three lances,
Blowing was carried out at 1400 Nm ³ /min at a firing point area/bath surface area = 70%, Ar gas was blown at 300 Nm ³ /hour from three nozzles at the bottom, and iron ore was introduced from the top.
In addition, at the tip of the first tank, slag generated from iron ore was timely discharged using a vacuum slag cleaner. In the subsequent second tank, the coal powder was injected into the bath iron using a top blowing lance, and the slag generated from the coal was continuously removed from the tip. In the third and final tank, quicklime and fluorite were injected into the hot metal using a top blowing lance, and the slag was removed from the tip using a slag cleaner. By returning the hot metal in the third tank to the first tank and repeating this process continuously, hot metal as shown in Table 5 could be efficiently produced from iron ore.

[Table] Example 5 A decarburization melting and refining tank, a carburization tank, and a desulfurization and dephosphorization tank with a bath diameter of 2.0 m and a bath depth of 2.0 m (L/D = 1.0) were made to almost the same level as shown in Figure 8. The hot metal is transferred to the decarburization tank → carburization tank, carburization tank → desulfurization and dephosphorization tank, and desulfurization and dephosphorization tank → decarburization tank. An electromagnetic induction coil was installed to ensure circulation. First, 30 tons of hot metal is initially charged into the tank so that the connecting pipes of each tank are on the hot metal surface, and then the initial level L ₁
The reactions shown in Table 6 were carried out in each tank.

[Table] The process was carried out while moving the hot metal between each tank at a speed of 20 tons per minute, and after one hour, 130 tons (final level L ₂ ) of molten steel (C = 0.10%, P = 0.25%, S = 0.010%) Since we were able to produce 100 tons of scrap iron from the decarburization tank into a ladle, we were able to continue melting scrap iron continuously. Example 6 The bath diameter is 2.3 m and the bath depth is 1.6 m (L/D
= 0.7), 50 tons of pre-treated hot metal is received in the refining furnace 101, and oxygen gas 102 is injected from the top at the steel bath hot spot area ratio.
0.70, and 25 tons of scrap and 2 tons of coke were continuously introduced from the upper part 103.
Adjusted the temperature of the steel bath during refining so that it does not exceed 1400℃. At the same time, 0.12N of Ai gas 104 was added from the bottom of the furnace.
The stirring of the steel bath was intensified by blowing through the tuyere at a rate of m ³ /t-min. After that, the refining is interrupted to discharge the slag generated in the refining furnace, and as shown in the figure, the slag in the furnace is completely removed by the vacuum slag machine 105, and then the scrap is removed from the upper part 103-2 in the same manner as described above. 25t,
Carburizing, melting and refining was carried out while adding 6 tons of coke, and we were able to produce 100 tons of hot metal. 7th
The operating conditions are shown in the table.

【table】

【table】 [Brief explanation of the drawing]

Figure 1 is a schematic diagram of the flash point area/bath surface area, Figure 2
Figures 3 and 4 show the differences in exhaust gas by L/D ratio.
A diagram of CO/CO ₂ +CO, FIG. 5 is a partial sectional view of an embodiment of the present invention, FIG. 6 is a partial sectional view of another embodiment of the present invention, and FIG. FIG. 8 is an explanatory diagram of still another embodiment of the present invention, and FIG. 9 is an explanatory diagram of still another embodiment of the present invention. 10; carburization tank, 12; slag drainage hole, 13; separation wall,
14, 25; Stirring gas bottom blowing hole, 24; Steel tapping hole.

Claims (1)

[Claims] 1. Maintaining L/D≧0.5 and S/LS≧0.5 during oxygen gas blowing in an oxygen top-blowing refining method that involves bottom blowing of gaseous substances and adding carbon material to hot metal. A method for carburizing, melting, and refining hot metal. However, L: Hot metal bath depth (m) D: Hot metal bath inner diameter (m) S: Hot spot area LS: Hot metal bath surface area 2 Oxygen top-blowing refining that involves bottom blowing of gaseous substances and adding carbon material to hot metal. In the method, L/D≧0.3 and S/LS≧0.3 are maintained during oxygen gas blowing, and the molten metal is kept at 1500 ml during decarburization refining using oxygen gas.
A hot metal carburization melting and refining method characterized by controlling the temperature to below ℃. However, L: Hot metal bath depth (m) D: Hot metal bath inner diameter (m) S: Hot spot area LS: Hot metal bath surface area 3 The amount of slag during decarburization refining with oxygen gas should be controlled to 15 kg or less per ton of molten steel. A method for carburizing, melting and refining hot metal according to claim 2.