JP4806945B2 - Method for producing low phosphorus hot metal - Google Patents

Description

  The present invention relates to a method for producing a low phosphorus hot metal in which a hot metal dephosphorization process is performed while melting scrap in a converter type vessel.

  Conventionally, a steelmaking method has been developed in which dephosphorization treatment (preliminary dephosphorization treatment) is performed in advance in the hot metal stage, and phosphorus in the hot metal is removed to some extent and decarburization blown in a converter. In this preliminary dephosphorization treatment, an oxygen source such as gaseous oxygen or iron oxide is added together with a lime refining agent (dephosphorization agent). This oxygen source reacts with carbon and silicon in addition to phosphorus in the hot metal to raise the hot metal temperature. However, since the dephosphorization reaction is thermodynamically lower in temperature, it is advantageous to add a coolant and treat it. The later temperature is controlled around 1300 ° C. In the pot type and torpedo type, the stirring is weak and it is impossible to add scrap as a coolant because the lance is charged into the bath. However, in the dephosphorization process using a converter type vessel, bottom blowing stirring And the lance is not charged in the bath, so that scrap can be dissolved.

Conventionally, as a method of melting scrap during hot metal dephosphorization using a converter type vessel, a refining agent mainly composed of decarburized soot and scrap having a width of 30 mm or less and a thickness of 15 mm or less are added, and blown gas Flow rate: 0.07 Nm ³ / min / t-pig or more, a method of performing hot metal dephosphorization treatment while stirring the bottom blowing gas (see, for example, Patent Document 1), a part of the dephosphorization agent, scrap and carbon material In addition, a method is proposed in which oxygen is blown up and the scrap is dissolved, and then the remaining dephosphorization agent is added to perform a dephosphorization process (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 1-147011 JP-A-1-316409

However, in the method of Patent Document 1, since it is necessary to reduce the size of the scrap, there is a problem that the processing cost is high for cutting and the like. Further, in the method of Patent Document 2, since the treatment period is divided into a scrap melting period and a dephosphorization period, the blowing time becomes very long and the productivity is greatly hindered.
As described above, the conventional technique for performing dephosphorization of hot metal while melting scrap has various problems. In particular, the hot metal temperature in the preliminary dephosphorization stage is about 1400 ° C. at the highest, and the temperature is lower than that of the decarburization process at a high temperature of 1600 ° C. or higher. Actually, dissolution occurs and it is hardly used.

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing low phosphorus hot metal that can perform hot metal dephosphorization while efficiently dissolving heavy scrap scrap. It is in.

  Conventionally, when performing dephosphorization treatment of hot metal while melting scrap, it is difficult to dissolve thick scrap such as heavy scrap, so it is necessary to limit to a very limited amount even if this is used, That was the mid-technical common sense. On the other hand, the present inventors examined a method of dephosphorizing while efficiently dissolving scrap by an experiment using a converter type vessel, in particular, a method of efficiently dissolving heavy waste, and as a result Contrary to the conventional recognition as described above, when scrap scrap whose weight waste ratio (mass ratio) is increased to 90% or more is used, it is completely expected that heavy scrap can be dissolved almost completely. I found outside facts.

The present invention has been made on the basis of such knowledge, and the gist thereof is that 10-30 kg / t-pig of a dephosphorizing agent as a CaO source is added to hot metal contained in a converter type vessel. spraying at a flow rate of 0.7~2.5Nm ³ / min · t-pig the top-blown oxygen gas or an oxygen-containing gas from the lance as the oxygen gas amount, and the furnace bottom or / and the stirring gas from the sidewalls 0.05 Dephosphorization of hot metal while blowing at a flow rate of ~ 0.3 Nm ³ / min · t-pig Processing time (however, when hot metal charging into the converter type vessel is completed – at the start of hot water after treatment) 10 It is a method that is performed in 20 minutes, and wastes (however, wastes are the grades HS, H1, and H2 in heavy wastes classified in the “Standardized Iron Scrap Inspection” established by the Japan Iron Recycling Industry Association) converter type volume percentage of points) of the 90 mass% or more scrap scrap It was charged to a low phosphorus molten iron manufacturing method, which comprises carrying out the dephosphorization process while dissolved in molten iron without causing undissolved the scrap debris.

  In the present invention, “heavy scrap” in scrap scrap is defined as grades HS, H1, and H2 in heavy scrap classified in “Iron Scrap Inspection Standard” established by the Japan Iron Recycling Industry Association. These heavy scraps are considered to be particularly difficult to dissolve when used in a dephosphorization process, and their use has been limited. The scraps other than “heavy waste” are H3, H4 heavy waste, press waste, shredder waste and the like as defined by the same standard.

  According to the method for producing low phosphorus hot metal of the present invention, it is possible to dissolve a large amount of heavy scrap that has been largely limited in the prior art. The restriction on the type is substantially eliminated, and an elastic operation is possible, and a large amount of scrap scrap can be dissolved to produce low phosphorus hot metal with high productivity.

In the method for producing low phosphorus hot metal of the present invention, a dephosphorizing agent is added to hot metal contained in a converter type vessel, oxygen gas or oxygen-containing gas is sprayed from an upper blowing lance, and the furnace bottom or / And dephosphorizing the hot metal while blowing a stirring gas from the side wall. Such a dephosphorization process itself is generally known as a method for efficiently producing low phosphorus hot metal, but in the present invention, scrap scrap with a weight scrap ratio of 90 mass% or more is charged into a converter type vessel. Then, the dephosphorization process is performed while dissolving the scrap waste in the hot metal.
As oxygen gas or oxygen-containing gas blown from the top blowing lance, pure oxygen, air, oxygen-enriched air, etc. can be used, but in view of thermal efficiency and dephosphorization rate, industrial pure oxygen is generally used. Is done.

  Usually, in the dephosphorization process, a plurality of types of scrap debris are used at the same time. However, the present inventors based on various experiments, the scrap debris used in the dephosphorization process is divided into heavy debris and other scraps. It has been found that the mass ratio with waste (light waste, etc.) greatly affects the dissolution of heavy waste. Specifically, when the total mass of scrap waste is constant, if there is a very small amount of heavy waste, it is naturally easy to dissolve, and as the proportion of heavy waste increases, undissolved residue occurs, and the proportion of heavy waste It was found that when the amount exceeds 20 mass%, the undissolved amount increases. However, although the amount of undissolved material increases as the percentage of weight waste increases further, contrary to expectation, the tendency reverses from around 50 mass%, and the amount of undissolved material decreases. It was found that most of the scrap was dissolved.

  This is considered to be due to the following reasons. First, if light wastes such as heavy waste and shredder are added at the same time, only the light waste dissolves from the initial stage, so the temperature of the hot metal is lowered, making it difficult for the waste waste to melt and leaving unmelted at the end of processing. . On the contrary, when only heavy waste is added, the scrap does not melt easily at the initial stage, so there is little decrease in hot metal temperature, and melting progresses in the middle and latter half when heat transfer to the scrap proceeds, and the processing proceeds. Upon completion, dissolution is considered complete. Accordingly, it has been found that in order to efficiently dissolve the heavy waste in the hot metal pretreatment stage at a low temperature, it is necessary to use only a small amount or to increase the ratio of the heavy waste to near the heavy waste alone. For this reason, in this invention, the scrap waste whose ratio of weight waste is 90 mass% or more is thrown into a converter type | mold container, and it is made to perform a dephosphorization process, dissolving this scrap waste in a hot metal.

  In addition, when undissolved scrap scraps occur at the end of the dephosphorization process, the scrap scraps impede the stirring of the hot metal, so not only the [P] concentration in the hot metal is difficult to decrease, but also the iron yield deteriorates. This may cause troubles such as impediments to evacuation and blockage of the bottom blowing gas nozzle. For this reason, generation | occurrence | production of the undissolved scrap scraps needs to be avoided as much as possible from the operational aspect.

Hereinafter, other refining conditions in the method of the present invention will be described.
In the method of the present invention, a dephosphorizing agent as a CaO source is added to hot metal contained in a converter type vessel, oxygen gas or oxygen-containing gas is sprayed from an upper blowing lance, and from the furnace bottom or / and the side wall. The dephosphorization process is performed while blowing a stirring gas (nitrogen, Ar gas, etc.). Here, it is considered that the scrap scrap solubility is easily affected by the amount of stirring gas, but according to the experiments by the present inventors, the amount of stirring gas is 0.05 Nm ³ / min · t-pig or more. As a result, it was confirmed that there was no hindrance to the dissolution of the weight waste. In addition, although there is no upper limit in particular in the amount of stirring gas, generally it is preferable to set it as 0.3 Nm < ³ > / min * t-pig or less from a viewpoint of refractory protection. Moreover, there is no problem if the treatment time (from the completion of the hot metal charging into the converter type vessel to the start of the hot water after treatment) is 10 minutes or more. Although there is no upper limit for the treatment time, it is generally preferably 20 minutes or less from the viewpoint of productivity. In addition, as other conditions, the dephosphorizing agent as the CaO source is 10 to 30 kg / t-pig, the oxygen gas amount from the top blowing lance is 0.7 to 2.5 Nm ³ / min · t-pig, and the processing is completed. The hot metal temperature at the time is about 1300 to 1400 ° C. is a normal level. As a method of introducing the dephosphorizing agent into the converter type vessel, an appropriate method such as so-called “top placement” or “projection with an upper blowing lance” can be adopted.

  The hot metal discharged in the blast furnace is desiliconized in the hot metal ladle, desulfurized in the hot metal ladle using mechanical stirring, and then in the converter type container 1 (capacity 300 t) having a structure as shown in FIG. The dephosphorization process which added the scrap waste was performed. The amount of scrap scrap added was 10 t (constant) per charge, and the ratio of heavy scrap in the scrap scrap was changed. After scrap scraps were charged into the converter type vessel 1 via a scrap chute (not shown), the hot metal 4 was received and treatment (blowing) was started.

In this dephosphorization process, the oxygen gas 6 is added to the hot metal 4 at a rate of 1.2 to 1.5 Nm ³ / min · t-pig using the top blowing lance 2 while the nozzle 3 embedded in the furnace bottom is used. Then, nitrogen gas 7 is blown in as a bottom blowing gas (stirring gas) at a supply rate of 0.08 to 0.12 Nm ³ / min · t-pig, and molten metal is charged into the converter type vessel for 10 to 12 minutes. The treatment was performed from the time of completion to the start of hot water after treatment. As the dephosphorizing agent 5, CaO was added in the range of 14 to 21 kg / t-pig according to the hot metal [Si] concentration before the treatment.

When the hot metal 4 was discharged from the converter type vessel 1 after the dephosphorization process, the presence or absence of undissolved scrap was visually examined. The results are shown in Table 1 together with the hot metal components / temperature and the ratio of heavy scrap in scrap scrap.
According to Table 1, depending on the ratio of heavy scrap in scrap scrap, the occurrence of scrap undissolved (after treatment) differs, and when the ratio of heavy scrap is increased, the scrap is less than 90 mass% of scrap scrap. While undissolved has occurred, scrap undissolved does not occur at all when the ratio of weight waste is 90 mass% or more.

Explanatory drawing which shows an example of the longitudinal cross-section of a converter type | mold container used for implementation of this invention method, and the dephosphorization process condition

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Converter type container 2 Lance 3 Nozzle 4 Hot metal 5 Dephosphorizing agent 6 Oxygen gas 7 Nitrogen gas

Claims (2)

10 to 30 kg / t-pig of a dephosphorizing agent as a CaO source is added to the hot metal accommodated in the converter type vessel, and oxygen gas or oxygen-containing gas is added as an oxygen gas amount from the top blowing lance to an oxygen gas amount of 0. Blowing at a flow rate of 7 to 2.5 Nm ³ / min · t-pig , and stirring gas from the furnace bottom or / and side wall at a flow rate of 0.05 to 0.3 Nm ³ / min · t-pig In which the dephosphorization process is performed for 10 to 20 minutes in the treatment time (however, when the molten metal charging into the converter type vessel is completed to the start of the hot water after the treatment) ,
The ratio of heavy waste (however, heavy waste refers to grades HS, H1, and H2 in heavy scraps classified in the “Standardized Iron Scrap Inspection Standard” established by the Japan Iron Recycling Industry Association) is 90 mass% or more. A method for producing low-phosphorus hot metal, characterized in that scrap debris is charged into a converter-type container, and dephosphorization is performed while dissolving the scrap debris in hot metal without causing undissolution. 14-21 kg / t-pig of a dephosphorizing agent as a CaO source is added to the hot metal contained in the converter type vessel, and oxygen gas is supplied from the top blowing lance to 1.2-1.5 Nm. ³ / Min · t-pig at a flow rate of 0.08 to 0.12 Nm from the bottom of the furnace ³ The hot metal dephosphorization treatment is performed for 10 to 20 minutes with the flow rate of / min · t-pig for 10 to 20 minutes (however, when the molten metal is charged into the converter-type vessel and when the hot water starts after treatment). The method for producing a low phosphorus hot metal according to claim 1.

Images