JP2011214023A - Dephosphorization method for hot metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dephosphorization method for hot metal by which dephosphorization efficiency can be improved even when an increase in slag quantity is suppressed by decreasing basicity.SOLUTION: Converter slag generated in decarburization refining of hot metal in a converter is crushed, dephosphorization refining agent containing ≥90 mass% of the crushed converter slag is injected into hot metal in a hot metal mixer car or in a hot metal ladle, and also collected dust generated from the hot metal mixer car is recovered, and a solid oxygen source containing the recovered collected dust is injected into the hot metal in the hot metal mixer car to remove the phosphorus in the hot metal.

Description

  The present invention relates to a method for pre-treating hot metal before decarburization blowing in a converter, and more particularly to a dephosphorization method for dephosphorizing hot metal.

  The hot metal melted in the blast furnace contains a large amount of impurities such as sulfur (S), phosphorus (P), and silicon (Si), and does not necessarily have a component composition suitable for the next steelmaking process. The component composition of the hot metal required in the steelmaking process varies depending on the component composition of the final molten steel, the steelmaking process, and the production efficiency. Therefore, it is necessary to perform a preliminary treatment for removing impurities in the hot metal before decarburization blowing in the converter.

  In the hot metal pretreatment, the desulfurization, dephosphorization, and desiliconization processes in which smelting vessel and in which order are performed are different in each steelworks. This is because the types of steel manufactured at the steelworks, the smelting equipment, and the physical distribution forms between the blast furnace and converter are different. As for the hot metal dephosphorization process, an optimum process is being sought according to the local conditions of each steelworks. A typical hot metal dephosphorization process is as follows.

  The scouring containers used in the dephosphorization process can be roughly divided into three types: a kneading wheel, a hot metal ladle, and a converter type dephosphorization furnace. Since the kneading car and the hot metal pan are originally transport containers, the free board is small. It is necessary to proceed with dephosphorization under a low oxygen potential and under weak stirring, and an injection method is employed in which an oxygen source is blown in order to secure a reaction interface area.

  On the other hand, in the case of a converter type dephosphorization furnace, a large free board is used to react slag and metal under strong stirring by top blowing oxygen and bottom blowing at a high oxygen flow rate. Phosphorus. Since it is advantageous for quick lime hatching compared to a kneading wheel or hot metal hot pot method, a method of adding a bulky flux from the top is common.

  By the way, in order to cope with the environmental impact represented by the recent global warming, there is a demand for reduction of slag emission in the steelmaking process. In order to reduce the amount of slag discharged, it has also been promoted to recycle the converter slag produced when decarburizing and refining in the converter to the hot metal dephosphorization process.

  For example, Patent Document 1 discloses that a decarburized soot generated when decarburizing and refining is performed in a first converter is cooled and solidified, and the cooled and solidified decarburized soot is used as a second converter for performing a dephosphorization process. A hot metal dephosphorization method is disclosed in which decarburized soot is added and recycled as a dephosphorization refining agent for the second converter. Since the decarburized soot contains a large amount of unreacted lime and has a low phosphorus content, a dephosphorizing effect can be expected during the hot metal dephosphorization treatment.

  In Patent Document 2, a dephosphorization scouring agent mainly composed of CaO is added to a converter type dephosphorization furnace, a gaseous oxygen source and a solid oxygen source are supplied as oxygen sources, and the dephosphorization scouring agent is hatched. There has been disclosed a dephosphorization method for hot metal in which slag is used and the hot metal is dephosphorized. Patent Document 2 describes that, as a dephosphorizing and refining agent mainly composed of CaO, a decarburizing soot generated when decarburizing and refining in a converter in the next step can be used.

JP 2001-240910 A JP 2007-154313 A

However, in the dephosphorization methods described in Patent Documents 1 and 2 in which decarburized soot is added to the converter dephosphorization furnace as a dephosphorizing refining agent, when the hot metal is to be made low-phosphorus, converter-type desorption is required. It is necessary to increase the basicity of the slag in the phosphorus furnace, and there is a problem that the amount of slag increases. Generally, in order to improve the dephosphorization efficiency of hot metal, it is necessary to increase CaO as a dephosphorizing agent. Since the slag basicity is represented by CaO / SiO _2, increasing the CaO as dephosphorization refining agent slag weight increases.

  Furthermore, in the dephosphorization method described in Patent Document 1, pretreatment for mixing iron oxide with decarburized soot is necessary, and if iron oxide is mixed in a slag pan, dust generation becomes a problem, and in the converter When iron oxide is mixed, the inside of the converter is cooled, so that the problem that slag adheres to the converter also arises.

  Therefore, an object of the present invention is to provide a hot metal dephosphorization method capable of improving the dephosphorization efficiency even if the basicity is lowered to suppress an increase in the amount of slag.

  In order to solve the above-described problems, one embodiment of the present invention is to remove a converter slag produced when decarburizing and scouring molten iron in a converter, and containing 90% by mass or more of the pulverized converter slag. Injecting the phosphorus scouring agent into the molten iron in the kneading wheel or hot metal ladle, collecting dust collection dust generated from the kneading wheel or hot metal ladle, and supplying the solid oxygen source containing the collected dust collecting dust to the kneading wheel or This is a hot metal dephosphorization method in which the hot metal in the hot metal ladle is injected to dephosphorize phosphorus in the hot metal.

According to the present invention, a dephosphorization refining agent containing 90% or more of decarburized slag (converter slag) is injected into the molten iron in the kneading wheel or the hot metal ladle so that the decarburized slag penetrates into the molten iron (As shown in FIG. 2, the line of equilibrium value Lp (P hot metal / slag distribution ratio) increases from (1) to (2)). For this reason, it is not necessary to raise the basicity CaO / SiO ₂ in order to reduce the phosphorus, and even lower phosphatization can be achieved with a slag amount equivalent to the conventional level using mixed lime as a dephosphorizing scouring agent. Further, it is not necessary to add a useless lime source, heat loss can be greatly improved, and low phosphorousity can be achieved after temperature compensation for the next step. Furthermore, while the dust collected once blown into the hot metal is recycled again, dephosphorization rate can be improved by concentrating components such as K and Cl which are advantageous for hatching, and oxygen source (oxidation) It is possible to reduce the dephosphorizing agent including iron.

1 is an overall view of a hot metal dephosphorization system according to an embodiment of the present invention. Graph showing the equilibrium value of phosphorus (relation between P concentration in hot metal after treatment and P ₂ O ₅ concentration in slag) Graph showing dephosphorization oxygen efficiency

  Hereinafter, an embodiment of the hot metal dephosphorization system of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows an overall view of a hot metal dephosphorization system.

  In the hot metal 2 in the kneading wheel 1, a powdery dephosphorizing scouring agent and powdered iron oxide are injected together with a carrier gas from the tip of the immersion lance 4.

  The powdery dephosphorizing and refining agent is obtained by solidifying the converter slag generated when decarburizing and refining the hot metal in the converter. The solidified converter slag is pulverized into, for example, a powder having a particle diameter of 3 mm or less through a crushing step and a pulverizing step. The pulverized converter slag 100% by mass of the dephosphorizing and refining agent is conveyed from the steelmaking factory by the lorry 10 and stored in the hopper 9. The component composition (mass%) of the dephosphorizing agent when the converter slag is 100 mass% is as follows.

  The dephosphorizing agent may contain 90% by mass or more of converter slag. If it is 10 mass% or less of a dephosphorization scouring agent, you may mix quicklime and calcium carbonate for adjusting basicity.

  The hopper 9 is also mixed with powdered iron oxide as a solid oxygen source. As the powdered iron oxide, pulverized sintered ore can be used. The sintered ore produced in the sintering factory is pulverized into powder and stored in the hopper 9 by airing or the like (not shown). In addition, iron ore, a mill scale, etc. can also be used as fixed oxygen sources other than a sintered ore.

  Dust collection dust (solid oxygen source) generated from the kneading vehicle 1 is also collected and mixed in the hopper 9. The exhaust gas generated from the chaotic vehicle 1 is sucked by the exhaust fan 12. Dust contained in the exhaust gas is collected by the dust collector 13. The dust collected by the dust collector 13 is stored in a dust collection hopper 17. The dust collected by the dust collector 13 may be stored in the hopper 9. The powdery dephosphorizing agent and the powdered iron oxide stored in the hopper 9 are injected into the kneading vehicle 1 together with a carrier gas such as air or nitrogen by the blowing dispenser 11.

  The dust collected in the dust collecting hopper 17 is mixed with a carrier gas such as air and nitrogen via a mixing line 18 (the conventional line in the figure) and an injection line 19 on the secondary side of the blow-in dispenser 11. 1 is directly injected.

  The timing of collecting dust collection dust generated from the kneading vehicle 1 and directly injecting it again into the kneading vehicle 1 is from the latter half of the dephosphorization scouring process, from the timing when the phosphorus in the molten iron becomes 0.050 mass% or less. 15 minutes before the end of phosphorus scouring. By injecting the dust collection dust, the solubility and wettability of the iron oxide is increased when the temperature in the latter half of the treatment is less than 1300 ° C. due to the effects of the elements K, Cl, etc. contained in the dust collection dust. Dust collection dust has a low oxygen content (oxygen source is reduced), and is therefore less effective at the rate of dephosphorization oxygen supply in the first half of the treatment, but is preferably improved in the second half.

  After collecting the dust collection dust generated from the kneading vehicle 1, the hopper 9 is in a state where the powdered dephosphorizing agent, the powdered iron oxide and the dust collection dust are stored. The powdery dephosphorizing scouring agent, the powdered iron oxide and the dust collecting dust are injected into the molten iron 2 in the kneading vehicle 1 together with a carrier gas such as air and nitrogen by the blowing dispenser 11.

By injecting a dephosphorizing scouring agent, iron oxide, and dust collection dust into the hot metal 2 in the kneading wheel 1, the oxidation reaction of phosphorus shown in the following (1) is promoted and a phosphorus oxide is generated.
2P + 5FeO = P ₂ O ₅ + 5Fe (1)

The produced P ₂ O ₅ is supplemented by CaO contained in the slag. Since a so-called dephosphorization reaction occurs, phosphorus can be removed stably.

FIG. 2 is a graph showing the equilibrium value of phosphorus (relation between the P concentration in the molten iron after treatment and the P ₂ O ₅ concentration in slag). The vertical axis of FIG. 2 is the concentration (mass%) of P ₂ O _{5 in} the slag, and the horizontal axis is the P concentration in the hot metal after processing (× 0.001 mass%). Line (1) shows the equilibrium value when mixed lime is used, and line (2) shows the equilibrium value when 100% converter furnace is used. It can be seen that in the line (2), P in the slag migrates and low phosphatization is more advantageous.

By injecting a dephosphorizing agent containing 90% or more of the converter soot, as shown in FIG. 2, the equilibrium value Lp (P hot metal / slag distribution ratio) line is changed from (1) to (2). To rise. For this reason, it is not necessary to raise the basicity CaO / SiO ₂ in order to reduce the phosphorus, and it is possible to reduce the phosphorus even with a slag amount equivalent to the conventional level using mixed lime as a dephosphorizing scouring agent. Further, it is not necessary to add a useless lime source, heat loss can be greatly improved, and low phosphorousity can be achieved after temperature compensation for the next step.

  Furthermore, the following can be said when basicity is taken into account when mixed lime is used and when converter slag is used. When mixed lime is used, if the basicity is 1.5, the equilibrium value becomes the line of (1), and considering the line (3) of the basicity of 1.5, it is possible to transfer P into the slag Then line (5) is obtained. Up to point B, line (1) is rate-determined, and after point B, line (3) is rate-limiting and synthesized (5) is the maximum P concentration in the slag.

  On the other hand, when a converter is used, if the basicity is 1.3, the equilibrium value is the line (2), and the line (4) with the basicity of 1.3 is taken into consideration, and P is added to the slag. What can be transferred becomes line (6) when combined. The line (2) is rate-limiting up to the point A, and after the point A, the line (4) is rate-limiting and the combined (6) is the maximum P concentration in the slag. From the above, it can be seen that P in the slag becomes higher and low phosphatization can be achieved even when the basicity is lowered when the converter furnace is used (C / S: 1.5 → 1.3). Moreover, when dust collection dust is added to 100% of the converter soot and dephosphorization is performed, the slag hatchability is further improved. The result is shown in Fig. 2. The one using 100% converter dust using dust collection dust (□ plot) is lower than the one using only 100% converter rod (plots (6) and ■). Have achieved.

  Since the temperature compensation is not sufficient with the above alone, it is possible to improve the dephosphorization amount for the same oxygen input amount by recycling the dust collection dust once blown into the hot metal, and useless oxygen. The source (iron oxide) can be eliminated. Alternatively, by utilizing the temperature loss reduction allowance, the success rate of the low phosphorus hot metal manufacturing can be increased by blowing the oxygen to the limit and blowing in the oxygen source.

FIG. 3 is a graph showing the dephosphorization oxygen efficiency. In FIG. 3, the horizontal axis represents oxygen-free oxygen (Nm ³ / t), and the vertical axis represents de-P oxygen efficiency (%). The horizontal axis represents the amount of oxygen excluding oxygen consumed for the desiliconization reaction from the amount of oxygen supplied (oxygen gas, sintered ore, etc.). The “deoxygenation efficiency” shown on the vertical axis is the amount of oxygen consumed in the dephosphorization reaction relative to the amount of oxygen that does not contribute to this desiliconization reaction by subtracting the amount of oxygen used in the desiliconization reaction from the amount of oxygen supplied. That is, the percentage of oxygen used to form P ₂ O ₅ .

The dephosphorization oxygen efficiency is represented by the following formula (2).
Dephosphorization oxygen efficiency (%) = amount of oxygen used for oxidation of phosphorus in hot metal (Nm ³ / t) / (total amount of oxygen blown into hot metal (Nm ³ / t) −oxygen used for oxidation of Si Amount (Nm ³ /t))...(2)

The measurement conditions are as follows. A large kneading vehicle is used, P concentration before treatment: 0.110 to 0.120 mass%, injection oxygen amount: 0.75 to 1.30 Nm ³ / t, Si concentration before treatment: 0.10 0.15% by mass.

  As shown in FIG. 3, without using dust collection dust, the de-P oxygen efficiency decreases with the increase in oxygen outside the Si removal, but the use of dust collection dust suppresses the efficiency drop and blows in excess iron oxide. It can be seen that a low P can be achieved while maintaining the temperature.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

  For example, in the above embodiment, the hot metal dephosphorization method of the present invention is performed using a kneading vehicle, but a hot metal ladle may be used instead of the kneading vehicle. The dephosphorization process of the present invention may be performed in combination with a desiliconization process or a desulfurization process.

An embodiment of a method for dephosphorizing hot metal using converter slag and dust collection dust will be described. After converter decarburization and refining of hot metal using quicklime as a slagging agent, the converter slag generated after discharging the molten steel into a ladle is discharged to a receiving cart, and the resulting converter slag is crushed. And pulverization was carried out to make the particle size 3 mm or less. A predetermined amount of converter slag was obtained and used as a CaO-based dephosphorizing agent. The composition of the converter slag of the powder, CaO: 43 wt%, SiO _2: 16 wt%, Al ₂ O _3: 3.5 wt%, P ₂ O _5: 2.5 wt%, MnO: 3 wt% MgO: 2 mass%, TiO ₂ : 1 mass%, T-Fe: 12 mass%, basicity (mass% CaO / mass% SiO ₂ ): 2.7. Using the CaO-based dephosphorizing refining agent with 100% by mass of the converter slag, as shown in FIG. 1 described above, dephosphorization of about 320 tons of hot metal contained in a kneading vehicle was performed. In the dephosphorization treatment, iron oxide dust was blown from the injection lance using dry air as a carrier gas, and CaO-based dephosphorization refining agent (converter slag 100% by mass) was blown and added from the injection lance using dry air as the carrier gas. Dust collection dust was blown in at 7.4 kg / t (per hot metal ton) from 15 minutes before the end of the dephosphorization until the end of the dephosphorization (example of the present invention). For comparison, hot metal dephosphorization treatment was also performed using a CaO-based dephosphorization refining agent in which the converter slag was 40% by mass and 60% by mass was powdered quicklime (comparative example). The dephosphorization method was the same as that of the present invention except that the CaO-based dephosphorizing agent used was different. The phosphorus concentration in the hot metal before the dephosphorization treatment was 0.110 to 0.120% by mass, and the phosphorus concentration in the hot metal after the dephosphorization treatment was 0.010 to 0.020% by mass in the examples of the present invention. Further, even when the basicity was 1.5 or less, it was possible to achieve a phosphorous concentration in the hot metal of 0.020% by mass or less. In the comparative example, the phosphorus concentration in the hot metal was the same, but the frequency of the number of times of deviating from the target was large, and the basicity was required to be higher than that of the present invention example. In addition, the present invention example can improve the dephosphorization amount with respect to the same oxygen input amount as the comparative example, and can reduce the amount of oxygen source (such as iron oxide).

1 ... Chaotic car (processing container)
2 ... Hot metal 4 ... Lance 9 ... Hopper 12 ... Exhaust fan 13 ... Dust collector 17 ... Dust collector dust hopper

Claims (3)

  The converter slag produced when decarburizing and scouring the hot metal in the converter is pulverized, and a dephosphorizing slag containing 90% by mass or more of the pulverized converter slag is injected into the hot metal in the kneading wheel or hot metal ladle. In addition, the dust collection dust generated from the kneading wheel or the hot metal ladle is collected, and a solid oxygen source containing the collected dust collection dust is injected into the hot metal in the kneading wheel or the hot metal ladle so that the phosphorus in the hot metal A dephosphorizing method for hot metal to dephosphorize the steel.   2. The hot metal dephosphorization method according to claim 1, wherein the basicity of the dephosphorizing agent is 1.5 or less. The hot metal dephosphorization method according to claim 1 or 2, wherein the dust collection dust is injected into the kneading wheel or the hot metal in the hot metal ladle in the latter half of the dephosphorization scouring.

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