JPH0555564B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention eliminates the bubbling phenomenon of slag (called slag forming), minimizes the unit consumption of powder used and the temperature drop during processing, and reduces oxidation loss of valuable metals such as manganese and iron. This invention relates to a method for desiliconizing hot metal that can reduce the amount of silicon. When dephosphorizing hot metal before being subjected to decarburization refining, it is usual to carry out a desiliconization treatment in advance in order to efficiently perform the dephosphorization. More specifically, it is preferable to perform the desiliconization treatment until the Si concentration in the hot metal becomes 0.2% or less, preferably 0.05% or less, and then dephosphorize it. In the conventional desiliconization treatment, a blast furnace cast bed trough, torpedo, ladle, etc. is used as the processing vessel, and in these vessels, the desiliconization agent can be applied using the overlay method, injection method, top blow projection method, etc. Various treatment methods have been adopted, and oxygen, iron oxide, or iron oxide containing 10 to 20% CaO is used as the desiliconizing agent. However, no matter which formulation is adopted, one of the common problems of conventional methods is slag forming. In other words, the slag foams during the desiliconization process. Conventionally, due to this slag forming,
The following operational problems were always involved. For example, when carrying out desiliconization treatment in a gutter, the desiliconizing agent introduced or projected into the gutter turns into slag in the gutter, and the desiliconization reaction also progresses, but the desiliconizing agent that has become a slag is transferred to a torpedo or ladle along with hot metal. The desiliconization reaction further progresses within this container due to the energy of this fall. However, the slag accumulated in the vessel causes forming, and a situation arises in which it is necessary to limit the amount of hot metal that is to be received in the vessel. usually,
Due to this slag forming, only about 70 to 80% of the intended amount of pig iron can be received in the vessel. As a result, the efficiency of transporting the hot metal is reduced and a large number of transport containers are required, and the temperature drop of the hot metal increases, resulting in a loss of thermal energy. Furthermore, in the event that slag overflows from a transport container and flows out of the container, it will require a great deal of effort and time to dispose of it afterwards, causing a major hindrance to operations. In order to prevent this from occurring, the amount of pig iron received has been further reduced in view of safety, and the amount of desiliconizing agent used has been restricted, which has become an obstacle to carrying out sufficient desiliconization treatment. are doing. Similar problems also occur in the case of the so-called injection method, in which a desiliconizing agent is added by blowing it into hot metal in a transportation container such as a torpedo. In fact, with this formulation, the flow of the slag is greater, so the degree of slag forming is higher, and the unit consumption of the desiliconizing agent is significantly limited. For this reason, it is no exaggeration to say that although the in-die extraction method is superior in terms of reaction efficiency, preventing slag forming is a priority issue in order to desiliconize to the desired silicon level. The basic cause of such problems lies in the composition of the desiliconizing agent used. In other words, in the conventional desiliconization treatment, it is necessary to ensure a sufficient oxygen source to oxidize the Si in the hot metal, and also from the viewpoint of flux slag formation and slag removal. Also, oxidizing agents for oxidizing Si in hot metal (e.g. iron ore, mill scale, iron sand,
The content of iron oxide (such as sintered ore powder) is increased, lime (CaO) is added at most 10 to 20%, and the basicity (CaO/SiO ₂ ) of the slag after treatment is adjusted to around 1. was normal. However, in such a low basicity slag, it is not possible to separate the silicate network in the slag, and the slag becomes vitrified. For this reason, CO gas generated by the reaction between the oxygen source in the slag and carbon in the hot metal or precipitated carbon contained in the slag is trapped in the slag, causing a significant bubbling phenomenon. In addition to this slag forming, under such low basicity slag, the oxygen potential on the slag side increases, so
A resulfurization phenomenon was also commonly observed, and manganese, a valuable metal, was also oxidized, and a demanganization reaction of about 70 to 120% of the amount of silicon removed usually occurred. These problems can basically be alleviated by increasing the CaO content in the desiliconizing agent used, but as mentioned above, with conventional formulations, the slagability deteriorates and the reactivity increases. In addition to this, the increase in CaO causes a relative decrease in oxygen sources, which reduces the oxidizing power for silicon oxidation and increases the cost of desiliconizing agents. However, the disadvantages such as the increase in CaO are greater, especially in the widely practiced method of desiliconization using gutters, which avoids increasing CaO. In addition, even in the injection method using an inert gas at a high solid-gas ratio, increasing CaO is difficult because the amount of oxidant for silicon oxidation is insufficient.
Even if it was added, the amount was kept to an extremely low level. The present invention was made with the aim of solving various problems in the conventional desiliconization treatment as described above, particularly problems such as slag forming, temperature drop during treatment, and oxidation loss of valuable metals such as manganese and iron. It is something. For this purpose, the present inventors have conducted numerous tests and researches, and found that instead of the conventional method of injecting a desiliconizing agent using an inert gas as a carrier gas, a predetermined method using an oxygen-enriched gas as a carrier gas. It was discovered that the aforementioned problems of conventional desiliconization methods could be completely eradicated by injecting powders with the same proportions, and a completely new desiliconization treatment method for hot metal could be established. That is, the present invention, as described in the claims, involves injecting powder containing solid iron oxide and CaO through a single pipe nozzle having a nozzle opening below the surface of the hot metal using an oxygen-enriched gas as a carrier gas. This is a desiliconization treatment method for hot metal supplied below the surface, in which the oxygen concentration (%O ₂ ) in oxygen-enriched gas is reduced to 40vol%.
Above, the solid-gas ratio (γ) of the powder and oxygen-enriched gas is 4 to 50.
g/Nl, and the ratio of the total amount of oxygen, which is the addition of the amount of oxygen in the oxygen-enriched gas and the amount of oxygen in iron oxide, to the blending ratio of CaO in the powder (ΣO ₂ /CaO) is 0.2. ~0.75Nl/
g. However, ΣO ₂ /CaO (Nl/g) is calculated using the following formula, (%O ₂ )/γ + (%IO) x (%O) x 0.7/100/(%C
aO), and in this formula, (%O ₂ ): Oxygen concentration in carrier gas (Vol%), (%IO): Iron oxide blending ratio in powder (wt%), (%CaO): Powder CaO blending ratio in the body (wt%), (%O): oxygen content in iron oxide (wt%), γ: ratio of powder to carrier gas (solid-gas ratio: g/
Nl), represents. The details of the present invention will be explained below. The desiliconization method of the present invention is a method in which powder containing iron oxide and CaO is injected using an oxygen-enriched gas as a carrier gas, and the basic feature is that this oxygen-enriched gas is used as a carrier gas. However, in addition, the oxygen concentration in the oxygen-enriched gas (%O ₂ ), the supply ratio of the oxygen-enriched gas (carrier gas) to the powder (solid-air ratio), and the ratio of the total amount of oxygen supplied to CaO By appropriately regulating (ΣO ₂ /CaO) at the same time, slag forming can be completely eliminated and at the same time extremely efficient desiliconization can be achieved. To illustrate the range of this condition, the first
Shown as shown. However, in Figure 1,
The oxygen concentration (%O ₂ ) in the oxygen-enriched gas is shown for a typical example of 80 Vol%. The reason why each condition is regulated as described above will be clear from the various effects shown in the examples below, but the outline thereof will be explained as follows. The present inventors conducted numerous experiments in which powder containing iron oxide and CaO was injected into hot metal using oxygen-enriched gas as a carrier gas, and found that the range in which slag forming occurs or does not occur is basically We found that it can be determined by ΣO ₂ /CaO. In other words, the formation behavior of forming can be comprehensively understood by the ratio of CaO to the total amount of oxygen supplied to the hot metal. According to experiments conducted by the present inventors, it was found that slag forming always occurs when the ΣO ₂ /CaO ratio exceeds 1.0, and does not occur at all when the ΣO 2 /CaO ratio exceeds 0.75. Further, when the ΣO ₂ /CaO ratio was about 0.8 to 0.9, slag forming could occur if the silicon concentration before treatment (hereinafter referred to as [%Si]) was about 0.5% or more. This is the reason why the upper limit of the ΣO ₂ /CaO ratio is set to 0.75. On the other hand, when the ΣO ₂ /CaO ratio is decreased, that is, when the amount of CaO is increased with respect to ΣO ₂ , the desiliconization oxygen efficiency (hereinafter referred to as η ^O2 _Si . This η ^O2 _Si is increased by Δ[%Si/
[corresponding to the ratio of ΣO ₂ ] decreases. The situation is shown in Figure 2. As seen in Figure 2, ΣO ₂ /
η ^O2 _Si shows the maximum value when the CaO ratio is approximately 0.5 to 0.6, and when the ΣO ₂ /CaO ratio is lower than this, the desiliconization and oxygen efficiency begins to decrease rapidly, and the ΣO ₂ /
When the CaO ratio becomes lower than 0.2, the oxygen efficiency decreases to such an extent that effective desiliconization is no longer possible.
The ΣO ₂ /CaO ratio needs to be 0.2 or more. Next, the reason why the solid-gas ratio (γ) is set to 4 to 50 is to suppress decarburization and to regulate η ^O2 _Si to an optimum value. That is, if γ is small, that is, if the flow rate of the carrier gas is increased unnecessarily, the decarburization reaction will increase. The aim of desiliconization treatment of hot metal is to oxidize silicon preferentially while suppressing decarburization, but making γ too small goes against this purpose. On the other hand, if γ is increased unnecessarily, that is, the amount of powder relative to the amount of carrier gas is increased unnecessarily, the amount of gaseous O ₂ necessary for the reaction will decrease, and the ΣO ₂ /CaO ratio will decrease (basicity ) resulting in
This results in a decrease in η ^O2 _Si . (%CaO) in powder
is 30 to 40%, the ΣO ₂ /CaO ratio is 0.4 to 0.5.
As γ of Max necessary to give the optimal value of
This is why we set the upper limit to 50. Regarding the oxygen concentration (%O ₂ ) in the carrier gas, the purpose of the present invention can be achieved even with pure oxygen, but considering the viewpoint of preventing blowing nozzle erosion and safety, the oxygen concentration in the carrier gas should be lower than that in actual operation. It is best to keep the upper level below 90Vol%. In addition, in order to obtain the effect of powder blowing with oxygen-enriched gas of the present invention, at least 40 Vol% or more, preferably
Requires oxygen concentration of 50Vol% or more. In addition, when injecting powder below the surface of hot metal using such an oxygen-rich carrier gas, there is a concern that the nozzle for this injection will be eroded. It was found that even when a nozzle was used, it was possible to achieve a better blowing effect than expected. In other words, when injecting powder into hot metal, inert gas has traditionally been used as a carrier gas due to the problem of nozzle erosion, and when injecting oxygen-enriched gas (blowing), However, due to the problem of melting due to the rapid generation of reaction heat, it was necessary to use a double tube (tuyere) and blow cooling gas (inert gas) through the outer tube. However, as in the present invention, when powder containing solid iron oxide and CaO is supplied below the surface of hot metal using oxygen-enriched gas as a carrier gas, from a single tube nozzle with a nozzle opening below the surface of hot metal. , the reaction heat due to the oxygen-enriched gas is considerably offset by the heat taken away by the latent heat and sensible heat of the powder.
Due to this heat removal, a hollow solidified shell containing the metal of the hot water is formed at the tip of the nozzle even if it is a single pipe nozzle made of refractory material, and this serves to effectively protect the nozzle refractory material. I found out. On the contrary, when the oxygen concentration in the carrier gas is lowered, this solidified shell may be produced excessively, and on the contrary, a situation may arise in which effective blowing cannot be performed. Therefore, in order to carry out effective injection without erosion of refractories, it is better to maintain the oxygen concentration in this oxygen-enriched gas at a high level than to lower it from the viewpoint of actual operation of the method of the present invention. is also desirable. The method of the present invention performs powder blowing under the above-mentioned formulation conditions, but even if these formulation conditions are adopted, it will be The present inventors have experimentally confirmed that the slag has poor slag-forming properties and the reaction efficiency is also poor. That is, in the method of the present invention, it is necessary to inject the hot metal below the surface of the hot metal under these mixing conditions. Figure 3 shows the relationship between the pre-treatment [%Si] and the basic unit of powder when injected below the hot water surface according to the method of the present invention, and the basic unit of powder here is: This is the amount of powder required to desiliconize [%Si] to 0.05% before treatment. In addition, this Figure 3 uses 45% CaO - 55% mill scale as the powder and calculates (%O ₂ ) under the solid-air ratio γ = 10.
The results are shown for three levels: 100, 80, and 50Vol%. When expressed as the ΣO ₂ /CaO ratio, this becomes 0.75, 0.42, and 0.31, respectively. As seen in the results in Figure 3, the amount of silicon removed is 0.4%.
The basic unit of powder required to obtain this is less than 25 kg/ton, which is a low level that could not be achieved using conventional methods. Therefore, although the CaO content ratio seems to be high in the method of the present invention, the basic unit amount of the powder as a whole may be significantly lower. In addition, in the conventional desiliconization method, [%Si] is 0.2
Normally, desiliconization efficiency drops significantly when desiliconization reaches a level of ~0.15%, and it is difficult to desiliconize below this level unless there is a serious problem.However, the method of the present invention In this case, [%Si] can be efficiently desiliconized down to 0.05%. This can significantly reduce the burden of subsequent dephosphorization treatment. The structure and effects of the method of the present invention will be specifically illustrated below with reference to Examples. The processing conditions and processing results of each example are summarized in Table 1 below. In the examples, a single tube nozzle made of refractory material was used as the furnace bottom nozzle in the example in which powder was injected with oxygen-enriched gas. Example 1 This example is a comparative example of addition to the hot water level. 20%CaO-80% sintered ore desiliconizing agent 40Kg/ton
It was added all at once to 170 kg of hot metal at 1340°C. And from the porous brick attached to the bottom of the container.
The bath was stirred by introducing Ar gas at a flow rate of 40 N/min. Approximately 3 minutes after the addition of the powder, the powder completely turned into slag and the desiliconization reaction proceeded, but after 9 minutes, a significant forming phenomenon occurred. The forming thickness reached 250mm against a bath depth of 400mm. Example 2 This example is a comparative example using only oxygen gas. Pure oxygen gas is supplied from the bottom of the furnace to 170 kg of hot metal.
A desiliconization experiment was conducted by blowing 50N/min. After injecting pure oxygen, a highly fluid slag was formed on the surface of the hot water. The slag started forming approximately 20 minutes after the start of blowing. The result was significant oxidation loss of manganese. Example 3 This example is a comparative example in which CaO is not used. Mill scale was injected into 170 kg of hot metal using pure oxygen as a carrier gas from the bottom nozzle of the furnace.
The oxygen gas flow rate is 80 N/min, and the mill scale supply rate is 500 g/min. Significant forming occurred approximately 6 minutes after the start of the experiment, and the forming height reached approximately 300 mm compared to the bath depth of 400 mm. Also, the oxidation loss of manganese was significant. Example 4 This example is a comparative example in which the ΣO ₂ /CaO ratio exceeds the range of the present invention. 20% CaO from the furnace bottom nozzle for 170Kg of hot metal
- Powder of 80% sintered ore was bottom-blown injected at a blowing rate of 360 g/min using 80 N/min of pure oxygen as a carrier gas. Significant forming occurred 12 minutes after the start of the experiment. Since the forming height exceeded the freeboard of 400 mm, slag had to be removed frequently. Example 5 This example is also a comparative example in which the ΣO ₂ /CaO ratio exceeds the range of the present invention. 25% CaO from the furnace bottom nozzle for 170Kg of hot metal
- Powder consisting of 75% mill scale was heated to 80N of pure oxygen.
Bottom blowing injection was carried out at a blowing rate of 450 g/min using a carrier gas of 450 g/min. Significant forming occurred 11 minutes after the start of the experiment. Example 6 Targeting 170 kg of hot metal, powder consisting of 50% CaO - 50% mill scale was added to the furnace bottom nozzle of the vessel using 80 N of oxygen-enriched gas of 80 Vol% O ₂ - 20 Vol% N _2.
Bottom blow injection was carried out at a blowing rate of 500 g/min using a carrier gas of 500 g/min. No forming occurred. Moreover, the produced slag was in a molten state and had relatively good fluidity. Example 7 Targeting 170Kg of hot metal, 40% from the furnace bottom nozzle
Powder consisting of CaO - 55% mill scale - 5% CaF ₂ was added at 400g/min using 80NVol%O ₂ -20Vol%N ₂ oxygen enriched gas as carrier gas.
Bottom blowing injection was carried out at a blowing speed of min. Forming did not occur at all, and a slag with excellent fluidity was formed. Example 8 170Kg of hot metal was targeted, and CaO was extracted from the furnace bottom nozzle.
Bottom-blown injection was performed using pure oxygen at 80 N/min as the carrier gas. Although no forming was observed, the slag produced became a powdery solid, and much of it adhered to the furnace wall. Example 9 Targeting 170Kg of hot metal, 40% from the furnace bottom nozzle
Powder consisting of CaO − 50% mill scale − 10% CaF ₂ was mixed with oxygen-enriched gas of 80 Vol % O ₂ − 20 Vol % N ₂
350g/min as a carrier gas of 80N/min
The bottom blowing injection was carried out at a blowing speed of .
No forming occurred at all, and a slag with excellent fluidity was formed. The processing conditions and processing results of Examples 1 to 9 above are summarized in Table 1. In the case of the method of the present invention, there was no slag forming, and
At a low slacks unit (desilicon removal unit) of 25Kg/ton, the amount of desiliconization (Δ[%Si]) is approximately
[%Si] in hot metal after treatment reached 0.4%.
It can be seen that the silicon is removed to 0.05% or less. Furthermore, the amount of manganese removed was small, and resulfurization did not occur, but rather there was even a tendency for desulfurization, and it is clear that desiliconization treatment can be carried out very effectively.

【table】

【table】 [Brief explanation of the drawing]

Figure 1 shows the oxygen concentration (%O ₂ ) in the carrier gas.
Figure 2 shows the condition range of the desiliconization method of the present invention, which shows the relationship between _{ΣO 2 /} CaO and the solid-gas ratio γ when is 80 ^Vol _% . Figure 3 shows the relationship between [%Si] before treatment and [%Si] =
FIG. 3 is a diagram illustrating the relationship between the powder unit consumption required to desilicate to 0.05% and the pre-treatment [%Si] according to the oxygen concentration in the carrier gas.

Claims (1)

[Scope of Claims] 1. A method for removing hot metal by supplying powder containing solid iron oxide and CaO to the surface of the hot metal using an oxygen-enriched gas as a carrier gas through a single tube nozzle having a nozzle opening below the surface of the hot metal. In the silicon treatment method, the oxygen concentration (%O ₂ ) in the oxygen-enriched gas is reduced to 40vol%.
Above, the solid-gas ratio (γ) of the powder and oxygen-enriched gas is 4 to 50.
g/Nl, and the total amount of oxygen (ΣO ₂ ), which is the sum of the amount of oxygen in the oxygen-enriched gas and the amount of oxygen in iron oxide, and the amount of oxygen in the powder.
The ratio to the CaO blending ratio (ΣO ₂ /CaO) is 0.2~
0.75Nl/g, a hot metal desiliconization method characterized by the following formula: ₍ %O ₂ )/γ + (%IO) O)×0.7/100/(%C
aO), and in the above formula, (%O ₂ ): Oxygen concentration in oxygen-enriched gas (vol.%), (%IO): Iron oxide blending ratio in powder (wt%), (%CaO): CaO blending ratio in powder (wt%), (%O): Oxygen content in iron oxide (wt%), γ: Ratio of powder to oxygen-enriched gas (solid-gas ratio: g/
Nl), represents