JPS63180345A - Dephosphorization method for molten iron - Google Patents

Abstract

PURPOSE:To suppress decarburization reaction and temp. drop of a molten iron and to permit an efficient dephosphorization treatment by immersing at least one of lances into the molten iron, blowing a dephosphorizing agent and gas simultaneously from said lance and pointing at least one of the other lance toward the surface of floating slag. CONSTITUTION:The dephosphorizing agent is blown with air, etc., as a carrier gas into the molten iron 8 by using at least one lance 12 among the lances to make slag off and dephosphorization of the molten iron at the time of subjecting the molten iron to the dephosphorization treatment in a molten iron vessel such as torpedo ladle car 2. At least one other lance 14 is pointed toward the surface of the slag 18 floating on the molten iron 8 and only the jet 20 of gaseous oxygen or the like is blown therefrom to burn the CO formed by the dephosphorization treatment. The blowing pressure of the lance 14 is controlled to a range where the exposing of the bar surface of the molten iron 8 by expelling the floating slag 18 is averted.

Description

[Detailed Description of the Invention] [Industrial Utilization] The present invention relates to a method for dephosphorizing hot metal, and particularly to a method for dephosphorizing hot metal stored in a volume type such as a pig iron mixer car or a ladle. Used in the field.

[Conventional technology]

In conventional converter operation using the top blowing method, WI
In order to utilize the Si in the pig iron as a heat source, the preliminary treatment of hot metal has mainly been carried out by desulfurization. However, in recent years, a combined blowing method of bottom blowing and top blowing has been implemented, and the hot metal pretreatments include desulfurization, desiliconization, and dephosphorization, and each hot metal pretreatment has a different type. Hot metal pretreatment is now performed using a treatment agent for each of the above treatments. This is because desulfurization treatment is a reduction reaction, whereas desiliconization and dephosphorization treatment are oxidation reactions and cannot be performed simultaneously.

Therefore, the dephosphorization treatment is generally carried out in an oxidizing atmosphere, using a specific refining agent to oxidize and remove P in the hot metal, which has been desiliconized using acidic slag.

The following two points are most important in such preliminary treatment of hot metal.

(a) Suppressing the decarburization reaction in order to retain a large amount of C, which serves as a source of thermal energy during converter operation.

(b) Minimize the temperature drop of hot metal.

In the past, many studies have been conducted on dephosphorization methods for hot metal, such as Japanese Patent Publication No. 42-16863 and Special Publication No. 46-1.
0771 etc. That is, CaO-Ca
It is well known that dephosphorization can be effectively carried out by basic slag having good fluidity using an F2-oxidizing agent, and that oxygen gas and/or solid oxygen such as iron ore or mill scale can be used as the oxidizing agent.

However, the above-mentioned conventional techniques for dephosphorizing hot metal have many problems that need to be improved. That is, in normal dephosphorization treatment of hot metal, the amount of slag forming agent and oxidizing agent input is large at 50 to 100 kg/l, and therefore a large amount of heat is required to dissolve the slag forming agent and decompose the solid oxidizing agent. As a result, the temperature drop of hot metal due to phosphor treatment is usually 50 to 1
It becomes a large one with a temperature of 50℃. A large drop in hot metal temperature is due to
Not only does it make the subsequent desulfurization treatment difficult, but it also significantly impedes the charging work into the converter in the next process and reduces the thermal energy of the hot metal. It is desirable that the temperature of the hot metal after treatment can be maintained at at least 1300°C or higher.

On the other hand, gaseous oxygen is often used as an oxidizing agent used as a dephosphorizing agent, and the method involves raising the temperature of the hot metal after treatment by injecting it into the hot metal as a carrier gas of Ca0-CaF or spraying it onto the surface of the hot metal. are also widely adopted. However, the dephosphorization oxygen efficiency using gaseous oxygen is much lower than that using solid oxygen from iron ore, mill scale, etc., and moreover, a large amount of C, which is an important heat source in hot metal, is burned, and the carbon after dephosphorization treatment is This results in a decrease in concentration. For example, in the "Continuous desulfurization and dephosphorization method of hot metal" disclosed in JP-A-58-16008, during dephosphorization,
In addition to injecting a dephosphorizing blank consisting of C&O1 iron oxide and a solvent, or a reaction accelerator and a carrier gas into the hot metal, the dephosphorizing blank made of C&O1 iron oxide and a solvent or a reaction accelerator is blown into the hot metal. de9 by intensively supplying oxygen using an oxygen top-blowing lance.
The slag floating on the surface of the hot metal is pushed toward the wall of the container by the oxygen upper stream generated by this operation, exposing the bare surface of the hot metal, where the dephosphorization reaction is carried out efficiently. It is said to be progressing well.

Further, Japanese Patent Application Laid-Open No. 59-50105 discloses a method in which gaseous oxygen is sprayed onto hot metal in a container to form localized areas on the bath surface where oxygen is excessively dissolved.

In all of these conventional methods, oxygen blowing is performed so that gaseous oxygen and hot metal come into direct contact, and although the temperature of the hot metal after treatment increases, the dephosphorization oxygen efficiency is poor due to gaseous oxygen. The decrease in C, which is an important heat source in the next step of converter operation, is an unavoidable problem.

[Problem that the invention seeks to solve]

The purpose of the present invention is to solve the problems of the above-mentioned conventional techniques in hot metal phosphorization methods, and to suppress the two most important points in hot metal pretreatment mentioned above, namely (a) decarburization reaction.

(b) Suppress the temperature drop of hot metal and take measures to raise the temperature.

To provide a method for dephosphorizing hot metal that satisfies the above requirements and enables effective dephosphorization.

[Means and operations for solving the problems] The gist of the present invention is as follows.

That is, in a method for dephosphorizing hot metal in which a dephosphorizing agent and gas are simultaneously blown into hot metal stored in a container such as a pig iron mixer through a lance, at least one of the lances is immersed in the hot metal. At the same time, the de9ization agent and the gas are blown in at the same time, and at least one other tube is directed toward the surface of the slag floating on the molten pig iron, and the pressure is suppressed to avoid exposing the bare surface of the molten pig iron. This method of dephosphorizing hot metal is characterized by dephosphorizing treatment while blowing only gaseous oxygen.

The present invention is based on the fact that the present inventors used a hot metal mixer type hot metal container and changed various methods for de9ization treatment of hot metal, and discovered the following fact during experiments. That is, (b) When an oxygen jet directly impinges on the hot metal surface in the presence of CaO-CaF2 slag or when blown into the hot metal bath, oxygen acts on both decarburization and dephosphorization, but
The dephosphorization oxygen efficiency, that is, the dephosphorization rate relative to the input oxygen amount, is 5 to 8%, which is significantly lower than the 12 to 19% dephosphorization oxygen efficiency using solid oxygen such as iron ore and mill scale. Therefore, in this case, the decarburization rate of hot metal is high.

(b) When the oxygen jet is moved away from the hot metal bath surface, secondary combustion of CO gas occurs within the vessel, and the thermal energy of this flame reaches the hot metal and raises the hot metal temperature. However, although the heat transfer efficiency of this flame to the hot metal is about 60%, decarburization of the hot metal does not occur at this time.

(c) By improving the oxygen injection lance and making it T-shaped to prevent the oxygen jet from colliding with the hot metal, C
When the container is filled with the secondary combustion flame of O gas, the heat transfer efficiency is further improved to reach 60 to 70%. To do this, place a lid with an opening for the lance on top of the container.
Heat transfer efficiency can be improved by sealing the inside of the container as tightly as possible.

As a result of research based on the above knowledge, we were able to complete the present invention.

The details of the invention will now be described with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view showing the situation in which hot metal is being dephosphorized according to the present invention when the container is a pig iron mixer and FIG. 2 is a ladle.

Ancillary equipment for a hot metal storage container when carrying out the present invention will first be described. For the pig iron mixer 2 shown in FIG. 1, a dust collection hood 6 is installed above the furnace mouth 4 to suck the generated gas, and a cover 10 is installed on the upper outer periphery of the furnace mouth 4 to prevent splashing caused by blowing of the hot metal 8. will be established. More preferably, the lance 12 for blowing dephosphorizing agent and the lance 1 for blowing gaseous oxygen
It is better to provide an insertion hole II (not shown) except for the insertion hole No. 4.

Take # shown in Figure 2! In the case of No. 3 as well, an M2C is provided at the top, and a dust collection hood 6 is provided to suck the generated gas.

The dephosphorization treatment of hot metal according to the present invention using the above-mentioned auxiliary equipment is carried out as follows. That is, at least one lance 12 inside the lance blows a demelting agent containing a mixture of CaO powder, CaF2 powder, and iron oxide powder into the hot metal 8 using air as a carrier gas. In this case, CaO is CaF2
and form a highly basic slag with good fluidity, reducing P in the hot metal.
is reacted with 0 in iron oxide to form a sludge and dephosphorize according to the following reaction formula.

3CaO+2P+50→3Ca(L p2o, ・=・−
(t) However, the generated CaO/P2O3 reacts with C in the hot metal, and a part of it is rephosphorous as shown in the following equation (2), and at that time, C
Generates O.

3 Ca0P205+ 5C-= 3 CaO+ 2
P+ 5 CO-- (21 Furthermore, in the non-contact part with the dephosphorizing agent, C in the hot metal reacts with iron oxide or gaseous oxygen to generate CO gas according to equation (3).

C+ v202-, CO・-・-・----(31(
At least one other lance 14 according to the present invention, which is dephosphorized and simultaneously generates CO gas by the reactions according to formulas 1), (2), and (3), is not immersed in the hot metal 8 and is As shown in FIG. 2, a gaseous oxygen jet 20 is directed toward the surface of the slag 18 floating in the hot metal 8.
The CO generated in the above equations (2) and (3) is combusted by the reaction in the following equation (4).

CO+v202-"CO2+68.2Ca#...-
・(41 At this time, the blowing pressure of the run 14 must be such that the slag 18 floating on the hot metal 8 is removed and the bare surface of the hot metal is not exposed. This is because if the bare surface of the hot metal 8 is exposed. At the same time as the dephosphorization reaction occurs according to equation (1), oxidation of C in hot metal 8 occurs according to equation (3), and Fe+O-*Fa
This is because the hot metal 8 is oxidized by the O 2 reaction, which is unfavorable in terms of Fe yield.

As mentioned above, in the preliminary treatment of hot metal in a vessel, it is necessary to minimize the drop in temperature of the hot metal. Therefore, using the lance 14 according to the present invention to increase the temperature of hot metal by burning the generated CO through the reaction of equation (4) brings about an extremely important effect.

The relationship between the top blowing oxygen consumption rate (Nm''/hot metal t hot metal layer pig iron temperature rise amount) due to gaseous oxygen blowing according to the inventors' experiments is as shown in Figure 3. In Figure 3, the straight line S represents the theoretical increase. The * mark is the actual value.As shown above, the CO gas generated during the dephosphorization process from the hot metal 8 is combusted with gaseous oxygen, and the generated heat is transferred to the hot metal 8 to increase the temperature of the hot metal. The effect it brings is the most important feature of the dephosphorization method according to the present invention.In order to make this effect more effective, the lance 14 for blowing gaseous oxygen should be used more than a straight lance as shown in Fig. 4(A). It is better to use a T-shaped lance as shown in Figure 4 (B) or a Y-shaped lance as shown in Figure 2, and it is also better to lower the blowing speed. It is preferable that the mouth is covered with a lid having openings for inserting the lances 12 and 14 to effectively burn the generated CO gas and heat the generated heat to the molten pig iron 8 as much as possible. According to their experimental results, it is possible to achieve a heat transfer efficiency of 60 to 70% of the calorific value.

Table 1 shows the predicted temperature rise of the hot metal 8 due to the upward blowing of gaseous oxygen by the lance 14, which was carried out by the present inventors using a 200-ton pig iron mixer.

However, the calculation results are based on the assumption that the heat transfer efficiency of the generated heat to the hot metal is 60%.

Table 1 From the results in Table 1, even if the temperature before pretreatment of hot metal including dephosphorization is at least 1320°C, if gaseous oxygen is blown at 25 N rn'/sin during dephosphorization, the temperature of hot metal can be lowered. It was found that the limit temperature of 1260°C can be secured, and in normal cases, the post-treatment hot metal temperature of 1300°C or higher can be secured.

〔Example〕

Comparative experiment in which hot metal No. 200 was charged into a mixing car, dephosphorization treatment according to the present invention was carried out after the completion of normal desiliconization treatment, and at the same time dephosphorization treatment according to the conventional method was also carried out to confirm the effect of the present invention. I did it.

The dephosphorization treatment according to the present invention is performed as shown in FIG.
The blowing according to No. 2 was carried out at the same time under the following conditions.

(1) Injection of dephosphorizing agent carrier gas (air): 1ONm''/win (2) Top blowing of gaseous oxygen 0: 25Nm/win A T-shaped lance as shown in Fig. 4 (B) was used, and even when using a straight lance, the blowing pressure was kept low so that no bare surface was exposed to the hot metal 8.
The conventional method for comparison was a method in which the dephosphorizing agent was blown under the same conditions, but only gaseous oxygen was not blown.

The amount of CO gas generated from hot metal using the above conventional method is 45~
5ONffI''/Illn, therefore, in the case of the method of the present invention, all of the generated CO gas is combusted, and 60 to 70% of its calorific value is transferred to the hot metal, contributing to its temperature rise, and increasing the temperature of the hot metal. We were able to significantly suppress the decline.

Figure 5 shows the dephosphorizing agent layer unit (Ca
It is a correlation diagram between the total amount of O1CaF2 and iron oxide powder (kg/t of hot metal) and the amount of temperature drop ('C) of hot metal during treatment.

As is clear from Figure 5, in the case of the conventional method without top blowing of gaseous oxygen, the amount of drop in the temperature of hot metal during treatment is:
6 when the dephosphorizing agent layer unit is as small as 20 to 30 kg/l.
The temperature is about 0 to 70°C, but when it increases to 50 to 60 kg/l, it reaches 100 to 120°C.

On the other hand, when using the method of the present invention, which involves blowing with gaseous oxygen in addition to blowing with a dephosphorizing agent, case B using a T-shaped lance is slightly better than case A using a straight lance. However, both methods have a much smaller increase in hot metal temperature than conventional methods and have fewer dephosphorizing agent layer units.
In the case of kg/l, the drop was 30 to 40°C, and even when the basic unit was 50 to 60 kg/l, the drop was 30 to 50°C, which was below the wheel load of the conventional method.

Next, the dephosphorization effect of hot metal by the method of the present invention is almost the same as that by the conventional method, and the changes in hot metal components before and after the dephosphorization treatment are as shown in Table 2.

As is clear from Table 2, the dephosphorization effect was reduced to 174 to 1/10 of the original content, sufficiently achieving the objective. The remarkable reduction in Si is the effect of the desiliconization treatment performed before the dephosphorization treatment. On the other hand, for problem C, 0.1~
Although there was a slight reduction of about 0.2%, there was almost no change, and it was possible to secure a sufficient amount of C without any problem in converter refining.

〔Effect of the invention〕

Modern pre-treatment of hot metal requires a number of processes such as desulfurization, desiliconization, and dephosphorization, and especially during dephosphorization, the amount of dephosphorization agents such as slag forming agents and oxidizing agents is required. As a result, a large amount of heat is required to dissolve and decompose these dephosphorizing agents, and as a result, the temperature of the hot metal decreases by 50 to 150 degrees Celsius. In view of the current situation where decarburization is performed at the same time, which hinders the operation of the converter in the next process, the present invention has been developed in addition to the conventional de9ization treatment in which a dephosphorizing agent is blown into hot metal using air as a carrier gas. In addition, we adopted a new dephosphorization method that simultaneously added an operation of gently blowing gaseous oxygen upward, resulting in the following effects.

(b) The CO gas produced by the oxidation reaction that occurs in part along with the dephosphorization reaction is combusted with top-blown gaseous oxygen, and 60 to 70% of the resulting calorific value is transferred to the hot metal to raise its temperature. The drop in temperature can be suppressed to a minimum of 50°C or less, making it possible to maintain a temperature of 1300°C or higher at all times.

(b) According to the method of the present invention, decarburization can be suppressed to a minimum, so sufficient C can be secured for the next process of converter refining,
Additional heat sources such as conventional coke and ferrosilicon are no longer required.

(c) The dephosphorization effect is comparable to that of conventional methods.

(d) In carrying out the present invention, only a gaseous oxygen top-blowing device is added to the conventional device, and no major modification of the equipment is required, and the slight increase in cost is more than compensated for by its great effect. be.

(e) By introducing the method of the present invention, problems such as problems with charging into a converter due to a drop in hot metal temperature after preliminary treatment have been eliminated, and stable handling of hot metal has become possible.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing the situation during the phosphorization process of hot metal stored in a mixing car according to the present invention, and FIG. 2 is a schematic sectional view showing the situation during the phosphorization process of the hot metal in a ladle according to the present invention. figure,
Figure 3 shows the top-blown oxygen consumption rate (N m'
/t) and the hot metal temperature rise (°C), and FIGS. 4(A) and 4(B) are schematic cross-sectional views showing how the lance for top blowing gaseous oxygen is used. A) shows a single-hole straight lance, and (B) shows a two-hole T-shaped lance. Figure 5 shows the basic unit before dephosphorization (kg
FIG. 2 is a diagram comparing the relationship between the amount of temperature drop ('C) of the hot metal during treatment and the amount of temperature drop ('C) of the hot metal during treatment with that of a conventional method. 2... Pig mixer car 4... Furnace mouth 6..., m
s Hood 8...Hot metal 12...Lance for blowing dephosphorizing agent 14...Lance for blowing gaseous oxygen 16...Lid 18...Slag 20...
・Gas oxygen jet

Claims (1)

[Claims] (1) In a hot metal dephosphorization method in which a dephosphorizing agent and gas are simultaneously blown into hot metal stored in a container such as a pig iron mixing car through a lance, at least one of the lances is immersed in the hot metal. At least the dephosphorizing agent and the gas are blown simultaneously, and at least one other tube is directed toward the surface of the slag floating on the hot metal to suppress the blowing pressure to a range that does not expose the bare surface of the hot metal. A method for dephosphorizing hot metal, which is characterized by performing sharp phosphorus treatment while spraying only gaseous oxygen.