JP6468083B2 - Converter discharge method - Google Patents

Description

  The present invention relates to a converter discharge method.

  In steel materials, the impurity P is a harmful element that reduces workability and toughness. Since the hot metal produced in a blast furnace or the like in the steel production process contains a large amount of P, dephosphorization is performed in the refining process, and the P concentration is reduced to a level necessary to satisfy the steel quality. . In order to cope with the stricter quality level required for steel materials, technological development for improving the dephosphorization efficiency has been actively conducted so far.

The dephosphorization reaction of P in molten iron is represented by, for example, the following formula (1). The underline indicates that it is a component in molten iron. That is, slag containing FeO is formed, and P in the molten iron is oxidized and removed to slag. Since P ₂ O ₅ is easily decomposed, CaO is added to the slag to stabilize P ₂ O ₅ and to prevent P from returning to the molten iron (rebound). Since this reaction is exothermic, the lower the temperature, the easier the dephosphorization proceeds.
2 P + 5FeO + 3CaO = 3CaO · P 2 O 5 + 5Fe (1)

  In the refining process, preliminary dephosphorization of dephosphorizing hot metal before decarburization is widely performed to improve the dephosphorization reaction efficiency, and the method uses a hot metal transport container such as a kneaded car (torpedo car) or hot metal ladle. And a system that uses a converter. Since the latter converter system has a larger internal volume than the former kneading wheel / hot metal ladle system, the hot metal and slag can be strongly stirred, and the processing time can be shortened. Furthermore, since oxygen can be supplied at a high speed, it is easy to increase the FeO concentration of the slag, and there is an advantage that the reaction of formula (1) is promoted and the lime for smelting can be reduced.

  As a converter-type hot metal dephosphorization method, Non-Patent Document 1 discloses a method of using two converters as dedicated furnaces for dephosphorization and decarburization (hereinafter referred to as dephosphorization-decarburization separation system). ing. In Non-Patent Document 2, after dephosphorization blowing, the converter is tilted to discharge only dephosphorization slag from the furnace port (hereinafter referred to as intermediate waste), and after the converter is returned to the vertical position, it is continuously removed. A method for performing charcoal blowing (hereinafter referred to as a dephosphorization-decarburization continuous method) is disclosed. In the dephosphorization-decarburization continuous method, there is no process for discharging and charging the hot metal after dephosphorization, so the non-operation time of the converter is short and there is no heat loss due to the transfer of hot metal. There is an advantage that the later slag is left in the furnace and can be reused as the next dephosphorizing blowing agent.

  The dephosphorization slag that remains in the furnace without being discharged by the intermediate desulfurization of the dephosphorization-decarburization system is carried over to the next decarburization blowing. It becomes easier to travel to the left side, and rebound from slag to hot metal occurs. For this reason, in decarburization blowing, additional CaO is added to advance the reaction of formula (1) to the right side. However, the more dephosphorization slag, the greater the amount of dephosphorization, so a larger amount of CaO must be added. No longer. Therefore, in the intermediate waste, it is desirable to efficiently discharge the slag and reduce the residual slag as much as possible, and a waste disposal method for that purpose is disclosed.

For example, in Patent Document 1, a method of scraping slag with a dragger used as a method for discharging a torpedo car or a hot metal ladle, and in Patent Document 2, a gas is blown from a plurality of tuyere provided on the furnace belly to discharge the slag. Patent Document 3 discloses a method for selectively discharging slag using electromagnetic force. In Patent Document 4, iron ore or a mill scale is added before evacuation to promote foaming of slag. In Patent Document 5, the basicity (CaO / SiO ₂ ) and Al ₂ O ₃ concentration of slag are set. There is disclosed a method of adjusting to a predetermined range and forming a slug property that is easy to form and rejecting. As described above, as the intermediate dephosphorization-decarburization intermediate method, the method of forcibly discharging slag by applying some external force and the method of increasing the volume by forming slag in the furnace before discharging It is roughly divided into two.

JP 59-13009 Japanese Patent Laid-Open No. 4-72007 JP 05-247514 A JP-A-4-350109 JP 2004-323959 A

Iron and steel, 76 (1990) No. 11, pp. 1817-1822 Iron and Steel, 87th (2001) No. 1, pp. 21-28

  However, the method of Patent Document 1 is not practical because the facility becomes too large considering the capacity of the converter. In the method of Patent Document 2, the tuyeres are installed on the furnace bell, so that the converter needs to be remodeled, and further, gas is constantly blown to prevent the tuyere clogging during blowing, resulting in increased costs. In the method of Patent Document 3, there is a problem that capital investment costs are incurred, and that it is difficult to use for a long time because it is in an environment of high temperature and vibration.

  Moreover, in the method of forming slag as in Patent Documents 4 and 5, since the slag once formed is calmed during evacuation and the evacuation efficiency is lowered, a large amount of slag is stably discharged. Was not easy.

  The present invention has been made in view of such circumstances, and after performing dephosphorization blowing of hot metal in a converter, when the converter is tilted and slag is discharged from the furnace port, a high discharge rate is obtained. It is an object to provide a method of exclusion.

The converter discharge method according to the present invention, which meets the above-mentioned object, forms the slag in the furnace by feeding the acid from the top blowing lance while leaving the molten iron in the converter after the dephosphorization treatment, and stops the feeding of oxygen. In the converter discharge method in which the converter is tilted and discharged from the furnace port, the slag has a composition of CaO / SiO ₂ = 0.8 to 1.2, Al ₂ O ₃ = 2 to 10%, In addition, the temperature is 1300 to 1400 ° C., and the tilt angle of the converter is once made smaller during the discharge, and then the pig iron is charged into the slag in the furnace in an amount satisfying the formula (2). This is a converter evacuation method characterized in that the converter is tilted and then evacuated by tilting the converter.

  According to the present invention, in the converter evacuation method, slag once sedated can be formed again, and the evacuation rate can be increased as compared with the prior art. Thereby, P in the slag carried over to decarburization blowing can be reduced, and the additional input amount of CaO can be reduced.

It shows a forming height and slag CaO / SiO ₂ relation Diagram showing the relationship between forming height and slag Al ₂ O ₃ concentration Diagram showing the relationship between forming height and temperature

Hereinafter, embodiments of the present invention will be described in detail. In dephosphorization blowing in a converter, oxygen in the hot metal is oxidized by blowing an oxygen jet onto the hot metal surface at a high speed and removed to the slag as P ₂ O ₅ . Since the hot metal contains C, Si, and Mn in addition to Fe, these elements are also oxidized, CO becomes exhaust gas, and SiO ₂ , MnO, and FeO form a slag phase. In addition, CaO is added to stabilize P ₂ O ₅ . Further, an MgO-based refractory is usually stretched on the converter inner wall. Therefore, the slag composition is a multicomponent system of CaO—SiO ₂ —FeO—MgO—MnO—P ₂ O ₅ .

At the interface between the hot metal and the slag, C in the hot metal and FeO in the slag react to generate CO gas (bubbles) by the reaction of the formula (3).
C + FeO = CO (g) + Fe (3)

  Further, a part of the hot metal is torn off by the sprayed oxygen jet to become granular iron. Since this granular iron contains C, CO gas is also generated from the interface between the granular iron and slag. When the bubbles generated in this manner stay in the slag, forming occurs and the slag expands. If the converter is tilted in this state, slag can be discharged efficiently from the furnace port. However, in order to tilt the converter, it is necessary to stop the acid supply and raise the lance, so that the supply of FeO to the interface between the hot metal and the slag and the generation of granular iron are stopped. For this reason, even if CO bubble generation continues in the initial stage of evacuation, the FeO concentration in the vicinity of the hot metal-slag interface gradually decreases, the C concentration in the granular iron decreases, and the precipitation of the granular iron occurs. Becomes weak and the forming gradually subsides. As a result, it is not easy to maintain the elimination speed after the middle stage of elimination.

  If the converter is returned to the vertical position after evacuation and blown again, slag can be formed and evacuated. However, it takes time, and productivity is greatly reduced.

  Therefore, the present inventors diligently researched a means for forming slag again without significantly reducing productivity, and if the pig iron is input from the outside after dredging, the slag can be formed again without reblowing. And found that the rejection rate can be increased. As used herein, “pig iron” includes, for example, blast furnace granule and mold iron. In order to achieve complete melting at the hot metal temperature (1250 to 1450 ° C.), the C concentration of pig iron is preferably 3 to 4.5% by mass from the viewpoint of the melting point. Moreover, 2-20 mm is suitable for the particle size of pig iron. Pig iron of less than 2 mm does not easily enter the slag, and it is difficult to generate CO bubbles from the inside. On the other hand, pig iron exceeding 20 mm quickly settles into the slag and reaches the hot water pool before melting, making it difficult to contribute to the generation of CO bubbles. When the ratio of 2 to 20 mm is 80% by mass or more, the effect of the present invention can be sufficiently exhibited.

  If pig iron having the above-mentioned C concentration and particle size is thrown into the slag from above the slag, it quickly melts inside the slag, and C contained in the pig iron reacts with FeO in the slag to react by the reaction of formula (3) CO bubbles can be generated and slag can be formed.

  As a charging method, for example, a scrap chute may be used, but after the discharge from the furnace port is completed, the furnace body may be once returned to a vertical position, and pig iron may be charged from a hopper on the furnace. In this case as well, pig iron quickly melts to generate CO bubbles and the slag forms again. Therefore, if the furnace body is tilted, the slag can be discharged. This method also does not require re-blowing, and a significant reduction in productivity can be avoided.

  Although a method of throwing pig iron from above the slag can be considered during the dredging, the thrown pig iron is washed away, and there is a very high possibility that it will be discharged out of the furnace before generating CO bubbles. Therefore, it is difficult for the injected pig iron to contribute to reforming. Rather, pig iron may generate CO bubbles in the waste pan that receives the discharged slag, forming slag and overflowing the slag from the waste pan, which may cause damage to peripheral equipment. Therefore, the method of throwing pig iron into the waste is not preferable.

In order to clarify the composition and temperature of slag suitable for forming, the inventors conducted experiments in a small furnace. That is, put 2 to 3 mm of granular pig iron into the slag melted in the iron crucible, immerse the iron rod in the formed slag, measure the change over time of the slag height from the adhesion height, and slag before throwing the pig iron The difference between the height and the maximum slag height after the introduction of pig iron was taken as the forming height. The results are shown in FIGS. The higher the forming height, the better the forming. From FIG. 1, it was found that the basicity (CaO / SiO ₂ ) of slag is preferably 0.8 to 1.2. Further, as shown in FIG. 2, the forming behavior changes The addition of Al ₂ O _3, it was found that 2-10% of the composition is preferred. Furthermore, as shown in FIG. 3, it turned out that 1300-1400 degreeC is suitable for temperature. Therefore, if the composition and temperature slag satisfy these conditions, the effects of the present invention can be enjoyed.

  The forming height of the slag is determined by the gas generation speed from the inside of the slag and the time during which the bubbles stay in the slag. The higher the gas generation speed or the longer the bubble staying time, the larger the forming height. According to the analysis of experimental data by the inventors, when the basicity of the slag increases, the slag viscosity decreases, so the flowability of the slag improves, the movement of FeO increases and the gas generation rate increases. Air bubbles are less likely to stay inside the slag. For this reason, there exists a range of basicity suitable for forming, and when the basicity is less than 0.8, the gas generation rate is low, and when it exceeds 1.2, the residence time of bubbles is low, so the forming property is lowered.

The same applies to the Al ₂ O ₃ concentration and temperature. As the Al ₂ O ₃ concentration increases, the slag viscosity increases. For this reason, when the Al ₂ O ₃ concentration is less than 2%, the bubble residence time is low, and when it exceeds 10%, the gas generation rate is low and the forming property is lowered. Further, since the slag viscosity decreases as the temperature increases, the gas generation rate is low below 1300 ° C., and the retention time of bubbles is low above 1400 ° C., resulting in a decrease in forming properties.

  Next, the amount of granular iron input was examined from the viewpoint of forming height suitable for evacuation. In order to discharge efficiently, the amount of granular iron is required to form slag to more than half of the distance (free board) from the hot bath stationary bath surface to the furnace port. However, if excessive grain iron is added, gas will be generated more rapidly than necessary, and the slag will be violently scattered around, making it extremely dangerous. When such excessive forming occurs, additional waste cannot be started until the gas generation has settled, so the waste time becomes longer and productivity is lowered. Therefore, there is an appropriate range for the input amount of granular iron.

When the amount of generated CO bubbles is the same, the forming height decreases as the cross-sectional area of the converter increases. Therefore, the amount of granular iron input depends on the free board and cross-sectional area of the converter. From this point of view, the amount of granular iron was examined, and the range of the formula (2) was found to be suitable. The amount of granular iron input in the formula (2) corresponds to the amount of CO gas generated necessary to form the slag in the furnace to a height suitable for waste within the range of the slag composition and temperature in the present invention.

  By putting an appropriate amount of pig iron from the outside into the slag in the furnace, the slag once calmed can be formed again, and the amount of slag can be increased.

As described above, in the converter discharge method according to the present invention, after the dephosphorization process, the molten iron is left in the converter, the slag in the furnace is formed by the supply of oxygen from the top blowing lance, and the acid supply In the converter discharge method in which the converter is tilted and discharged from the furnace port after the slag is stopped, the slag has a composition of CaO / SiO ₂ = 0.8 to 1.2 and Al ₂ O ₃ = 2 to 10%. In addition, the temperature is 1300 to 1400 ° C., and the tilt angle of the converter is once made smaller during the discharge, and then the pig iron is charged into the slag in the furnace in an amount satisfying the formula (2). After the slag is formed again, the converter is tilted and discharged.

Here, the slag forming in the furnace due to the acid sent from the upper blowing lance can be realized by carrying out the acid feeding used in the dephosphorization refining performed normally. In addition, if the steel to be melted is a normal cultivar that is not specially aimed at low phosphorus reduction, the slag composition at the end of dephosphorization will be CaO / SiO ₂ = 0.8 to 1.2. Refining may be performed by adding a refining material. Regarding the point of setting the slag temperature at 1300 to 1400 ° C at the time of slagging, calculate the heat balance before and after refining, and introduce coolant such as iron ore so that the molten iron temperature at the end of dephosphorization refining will be in the temperature range This can be realized.

The content of Al ₂ O _{3 in} the slag at the end of dephosphorization is around 2%. Therefore, it is not necessary to add an Al ₂ O ₃ source when it can be predicted that the content of Al ₂ O ₃ at the end of dephosphorization will be 2% or more from the composition of raw materials and smelting materials used for refining, When there is a possibility that the Al ₂ O ₃ content in the slag is less than 2%, an Al ₂ O ₃ source is added. The Al ₂ O ₃ source may be input during dephosphorization blowing, for example, secondary refining slag may be used. And Si concentration of the molten iron to be charged into the converter, the amount and composition of the refining material to be introduced into the dephosphorization blowing estimate the composition and amount of dephosphorization slag, of Al ₂ O ₃ source previously analyzed If the Al ₂ O ₃ concentration is used, it is possible to determine the input amount of the Al ₂ O ₃ source in which the dephosphorization slag has an Al ₂ O ₃ concentration of 2 to 10% by mass.

Examples of the present invention will be specifically described below based on Table 1. The shape of the converter used for refining is that the distance between the hot metal surface and the furnace port is 8 m, the height from the bottom of the converter to the hot metal stationary surface is 2.3 m, and the maximum horizontal cross-sectional area of the converter is 33 .2 m ² .

Hot metal was charged into the converter and dephosphorized and blown to form slag. The amount of refining material such as quick lime charged into the converter during dephosphorization refining was adjusted so that the slag in the converter at the end of dephosphorization refining was adjusted to the value shown in Table 1. Further, secondary refining slag was added during dephosphorization refining as necessary to adjust the content of Al ₂ O ₃ in the slag.

  The hot metal temperature at the end of dephosphorization was adjusted to the temperature shown in Table 1. After the dephosphorization and refining, the acid feeding was stopped, the converter was tilted, and slag was started to be discharged from the furnace port to the bottom ladle. Thereafter, in the middle of evacuation, the tilt angle of the converter was made smaller than that at the time of evacuation, and evacuation was interrupted, and pig iron (C concentration: 4.3 mass%) was put into the furnace from a scrap chute. Then, the converter was tilted again and additional evacuation was performed.

なお、炉内スラグの重量は、生石灰などの投入した精錬材の重量と、採取したスラグの成分値から物質収支を計算して求めた。 The weight of the discharged slag was measured after cooling, and the rejection rate was evaluated by equation (4).

The weight of the slag in the furnace was obtained by calculating the mass balance from the weight of the smelted material such as quick lime and the component value of the collected slag.

  The present invention is intended for melting general steel that is not low phosphorous steel, and high dephosphorization performance is not required. Therefore, the target of the rejection rate is set to 55% or more.

  Table 1 shows the results of the processing. The underline in the table represents a part that is outside the scope of the present invention. Examples 1 to 8 are invention examples, and the treatment conditions were within the scope of the present invention, so the rejection rate was 55% or more.

On the other hand, Examples 9 to 17 are comparative examples. In Example 9, as a result of not performing re-forming by introducing pig iron, the rejection rate was only 50%. Examples 10-11 were CaO / SiO ₂ of slag, Examples 12-13 were Al ₂ O ₃ concentrations of slag, and Examples 14-15 were slag temperatures outside the scope of the present invention, so the rejection rate was 55 %. In Example 16, since the amount of granular iron fell below the lower limit of the present invention, reforming was weak and the rejection rate was less than 55%. In Example 17, since the amount of pig iron exceeded the upper limit of the present invention, reforming was intense, and a waiting time occurred until the converter was tilted. As a result, although the rejection rate was high, the rejection time increased significantly.

Claims (1)

After the dephosphorization process, the molten iron remains in the converter, the slag in the furnace is formed by sending acid from the top blowing lance, and after stopping the feeding, the converter is tilted and discharged from the furnace port. In the dredging method, the slag has a composition of CaO / SiO ₂ = 0.8 to 1.2, Al ₂ O ₃ = 2 to 10%, and the temperature is 1300 to 1400 ° C. Make the tilt angle of the furnace smaller than that at the time of evacuation, and then throw pig iron into the slag in the furnace in an amount that satisfies the formula (2). After forming the slag again, the converter is tilted to perform slagging. A method for rejecting a converter.

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