KR100775240B1 - Hot metal pretreatment for improving desulfurizing efficiency - Google Patents

Abstract

The present invention relates to a molten iron preliminary treatment method for degassing the blast furnace molten iron to topeka before charging to the converter, the object of the present invention is to increase the basicity of the molten iron slag by adding the converter slag to the molten iron slag before the deflow treatment It is to provide a molten iron preliminary treatment method for improving the degassing efficiency by lowering the viscosity of the slag.

In the present invention for achieving the above object, in the method of preliminary treatment by releasing the molten iron of the blast furnace with topedoca, the step of injecting the converter slag 1.0 to 2.0kg per ton of molten iron of the topedoca, to the molten iron The technical gist of the present invention relates to a method for preliminary treatment of molten iron for improving the degassing efficiency, comprising the step of introducing a desulfurizing agent.

Pretreatment of molten iron

Description

Hot metal pretreatment for improving desulfurizing efficiency

1 is a manufacturing process diagram from the blast furnace to continuous casting.

Figure 2 is a schematic diagram of the dehydration operation by blowing the powder in the molten iron preliminary treatment process.

3 is a graph showing the distribution ratio of [S] according to the basicity of molten iron slag.

Figure 4 is a schematic diagram of the deflow reaction at the molten iron / slag interface in the conventional deflow treatment process.

Figure 5 is the role of the wind slag when the slag is injected in accordance with the present invention and

       Schematic of dehydration reaction.

Figure 6 shows the reaction efficiency of the basicity and the desorbent according to the converter slag dosage

       Schematic diagram.

 7 compares the dehydration rate and the desorbent reaction efficiency during the input of the wind-chain slag

Graph shown.

* Description of the symbols for the main parts of the drawings *

           10 ..... storage tank 20 ..... dispenser

30 ..... Topedoka 40 ..... Injection Lance

The present invention relates to a molten iron preliminary treatment method for degassing the blast furnace molten iron to Topedoka before charging to the converter, and more specifically, to increase the basicity of the molten iron slag by injecting the converter slag into the molten iron slag prior to dewatering treatment It relates to a molten iron preliminary treatment method for improving the degassing efficiency by lowering the viscosity of the molten iron slag.

The blast furnace steelmaking method consists of a steelmaking-steelmaking-continuous casting process as shown in FIG. The chartered ship from the blast furnace to Topedoca is pretreated with delineation and dewatering before charging the converter. This process is called charter pretreatment. Pretreatment of the molten iron before charging it to the converter is because sulfur is removed by the reduction reaction, whereas the converter for oxygen scavenging has a strong oxidizing atmosphere, so that the dehydration reaction in the converter is limited. As a result, since significant desulfurization effects cannot be expected in the converter furnace, it is necessary to lower the sulfur content of the molten iron charged into the converter in the molten iron preliminary treatment process in order to manufacture the cryogenic steel.

In the charter preliminary treatment, dehydration treatment is increasing in order to secure the internal quality of slabs and lower sulfur susceptibility sensitive to the brittleness of steel as the quality requirements for steel have become stricter. In particular, in the production of ultra-low flow steel of about 50 ppm or less of sulfur, the desulfurization operation is being strengthened in the charter preparation process in order to reduce the process load in the secondary refining after the converter is pulled out.

An example of the degassing treatment method by blowing the powder in the pretreatment process is shown in FIG. 2. The molten iron desorbent (CaO or CaC ₂ ) of the powder is blown into the molten iron, such as nitrogen gas, by a lance hole in which the lance 40 is deposited on the molten iron of Torpedo. To reduce sulfur. There are two major dehydration reactions. That is, there is a transient dehydration reaction with the sulfur of the molten iron at the desorbent interface blown into the molten iron and a permanent dehydration reaction occurring at the slag and the molten iron interface above the molten iron. Temporary dehydration occurs only when the desorbent is added, while permanent dehydration occurs continuously.

The deflow reaction formula of the molten iron desorbent generally used is as follows.

[When using CaC ₂ powder]

CaC ₂ + S = CaS + 2C

CaC ₂ + FeS = CaS + 2C + Fe

[When CaO powder is blown]                         

2FeS + 4CaO + Si = 2Fe + 2CaS + Ca2SiO ₄

2FeS + 2CaO + Si = 2Fe + 2CaS + SiO ₂

However, the basicity of the slag which flowed out from the blast furnace, that is, the slag basicity (CaO / SiO ₂ ) before the dehydration treatment, was low at an average of 1.10 (0.80 to 1.35). As shown in FIG. 3, the lower the basicity of the slag, the lower the sulfur trapping ability. In particular, when degreasing the molten iron in the blast furnace, the basicity is lowered to 0.80 (0.34 to 1.13) by SiO ₂ generated by the desilification reaction, which further lowers the degassing efficiency. De-silification industry is to lower the silicon ([Si] component of molten iron before charging the converter in order to reduce the slipping generated in the converter operation, the reaction formula is as follows.

[Si] + 2FeO (Solid Oxygen) → SiO ₂ + 2Fe

Due to the SiO ₂ produced as a reactant in the above desulfurization treatment, the amount of slag is also increased compared to general molten iron, so the degassing efficiency is low, thereby increasing the load during the degassing treatment such as an increase in the amount of desorbent and an increase in the degassing treatment time.

Therefore, in the conventional molten iron non-treatment process, the slag of the low base degree was removed and subjected to the deflow treatment before blowing the desorbent. However, in order to perform slag excavation work, it takes about 15 minutes to perform separate slag excavation equipment and slag excavation work, which acted as a factor that lowers the overall productivity.

The present invention is to provide a preliminary treatment method to improve the degassing efficiency by reforming the molten iron slag without the slag excavation work in the case of molten iron in the molten iron preliminary treatment step, the object is.

The pretreatment method of the present invention for achieving the above object,

Injecting converter slag 1.0 ~ 2.0kg per ton of molten iron from the top of the chartered topedoka,

It is configured to include the step of dewatering by introducing a desorbent to the molten iron.

Hereinafter, the present invention will be described in detail.

In the research process to improve the degassing reaction efficiency, the inventors of the present invention not only have low sulfur collection capacity ([S] Capacity) in the molten slag of low viscosity but also high viscosity, and the molten iron slag is coated with a desorbent as shown in FIG. And lowering the reaction area by coordinating the floating desorbent.                     

Based on the results of this study, converter slag, especially particles and spherical wind-clad slag, was added to the molten iron slag. As a result, the reaction surface area was wide, and as shown in FIG. 5, the reforming effect of the molten iron slag was large. there was.

In the present invention, the converter slag is introduced into the molten iron slag before the dewatering treatment of the molten iron taken out of the topedoca in accordance with a conventional method. Of course, the present invention is applied regardless of the presence or absence of desulfurization treatment when departing from the blast furnace to topedoca.

Converter slag has high basicity and is divided into general slab and wind-chain slag. General slag is a crushed by drying and cooling the converter slag. In addition, the blow-off slag is blown by a separate blow-off treatment apparatus by excluding the molten converter slag remaining in the furnace after the blowing and tapping in the converter. The air blowing treatment blows out the high speed air stream while dropping the molten converter slag. The difference between the normal slag and the wind slag is different in the size and shape of the particles, an example of the components are shown in Table 1.

division shape size main ingredient(%) Melting point Windbreak Slag Ball type 1 ~ 4mm≥90%, 1mm or less≤10% T.Fe: 18 to 25%, CaO: 38 to 46, SiO ₂ : 8 to 15%, MgO: 7 to 10%, other Al ₂ O ₃ etc. (base degree 3.5) 1350 ℃ General slag Square 5 ~ 15mm≥90% Others≤10%

In the present invention, it is preferable to use air-chain slag in consideration of the fact that the particles are small and the spheres have a wide reaction surface area.

According to the present invention, it is preferable to add 1.0-2.0 kg of molten slag to the molten iron slag. When the input amount of the converter slag is less than 1.0 kg / melting-ton, the increase of basicity is not large, and thus the desorbent reaction efficiency is low, and when more than 2.0 kg / melting-ton is added, as shown in FIG. Rather than increasing the basicity or lowering the viscosity, the temperature is reduced to reduce the deflowing efficiency.

After the converter slag is introduced into the molten iron slag as described above, the desulfurizing agent may be added by a conventional method, and the degassing treatment may be performed. As converter slag injected through bubbling operation is stirred with molten iron slag, the molten slag of high viscosity and low base airway is reformed into molten slag of low viscosity and high base airway, so that the dewatering ability in slag and molten iron surface is increased even after blowing the desorbent powder. Because. Bubbling is preferably about 2 to 3 minutes in order to see the full effect of the wind slag. Of course, the longer the bubbling, the better in terms of reforming the molten iron slag, but excessive bubbling can increase the life of the lance and increase the working time.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

The components and arrival temperatures of the molten iron which has been chartered in the blast furnace and arrived at the molten iron preliminary treatment process are shown in Table 2 below.                     

division C Si Mn P S Temperature (℃) ingredient 4.0 ~ 4.5 0.25-1.00 0.25-0.45 0.090-0.110 0.015 ~ 0.050 1350-1450

In the molten iron of Table 2, the above-mentioned wind-breaking slag and general converter slag were added according to the method of Table 3.

division                                              Operation method Conventional method Arrive at the depot → Sampling → Lower the lance and blow the desorbent powder → Complete the blow up and raise the lance → Sampling → Departure Inventive Example One Arrival at the depot → Sampling → Blowing slag into the upper part of Topedo → Lowering the lance and blowing the desorbent powder → Complete the blow and raise the lance → Sampling → Departure 2 Arrival at the depot → Sampling → Blowing slag into the top of Topedoca → Lance descent and total bubbling (2 ~ 3 min) → Blowing out the desorbent powder → Blowing up and lance rise → Sampling → Departure 3 Arrival at the depot → Sampling → Blowing slag into the top of Topedoca → Lance descent and total bubbling (5-6 minutes) → Deodorant powder injection → Blow up and lance rise → Sampling → Departure

According to the method of Table 3, 1.0kg of the wind-chain slag per ton of molten iron of Table 1 was added, followed by CaO-based desorbent and the results are shown in Table 4.

division Before desulfurization [S] After degassing [S] Desorbent Unit Discharge rate Desorbent Reaction Efficiency Conventional 205 ppm 55 ppm 9.09 kg / melt-ton 73.0% 2.90% Inventive Example 1 212 ppm 43 ppm 8.84 kg / melting-ton 79.7% 3.34% Inventive Example 2 210 ppm 35 ppm 7.88kg / melt-ton 83.3% 3.89% Inventive Example 3 198 ppm 32 ppm 7.44kg / melt-ton 83.8% 3.90%

여기서, M_x(x의 분자량), W_steel(용선 선출량, kg), W_cax(CaO 또는 CaC₂ 투입량, kg), [%S]_i,f(탈류전, 후 [S] 농도, %)

Where M _x (molecular weight of x), W _steel ( _melting elect, kg), W _cax (CaO or CaC ₂ dose, kg), [% S] _{i, f} (concentration before and after [S],% )

As shown in Table 4, Inventive Example 1, particularly Inventive Examples 2, 3 shows excellent dehydration rate and desorbent reaction efficiency compared to the prior art.

Example 2

In the same manner as in the method of Inventive Example 2 of Table 3 of Example 1, the input amount of the air chain slag, the basicity change of the slag after dehydration, and the reaction efficiency of CaO desorbent were shown in FIG. 6.

As can be seen in Figure 6, the basicity after degassing with the addition of the air-chain slag increases, but the degassing agent reaction efficiency increased and then gradually decreased the amount of the air-chain slag. This is because, when the amount of blown slag is increased, the amount of blown slag is 1.0 ~ 2.0kg / melter-ton in terms of the efficiency of dewatering, since the temperature is reduced to reduce the degassing efficiency rather than lowering the viscosity of molten iron slag or increasing the basicity. Most advantageous.

Example 3

When the dehydration treatment by the conventional method, the desorbent reaction efficiency and the two types of slag in Table 1 were compared before the desorbent input and the reaction efficiency when bubbling is shown in Table 5.

Molten iron General charter ships Degreasing Charter Conventional example Inventive Example 4 Inventive Example 5 Conventional example Inventive Example 6 Inventive Example 7 Use CaC ₂ TLC number 52 21 7 16 8 6 Before desulfurization [S] (10-3%) 21.0 20.0 18.7 20.0 19.1 20.0 After degassing [S] (10-3%) 3.1 3.4 3.3 4.3 3.4 4.4 Desorbent Unit (KG / T-P) 5.69 4.59 4.67 5.78 5.47 5.59 Desorbent Reaction Efficiency (%) 5.57 6.16 5.69 4.74 4.98 4.88 CaO use TLC number 82 10 10 68 14 10 Before desulfurization [S] (10-3%) 20.6 20.7 21.7 19.5 19.2 19.8 After degassing [S] (10-3%) 4.2 4.5 4.7 4.6 4.1 4.5 Desorbent Unit (KG / T-P) 9.36 7.59 8.92 10.32 8.29 8.67 Desorbent Reaction Efficiency (%) 3.05 3.67 3.34 2.53 3.14 3.09

As shown in Table 5, in the case of invention examples (4, 6), it is a case where a wind-chain slag is used, and in the case of invention examples (5, 7), it is a case where a general slag is used.

In the case of Inventive Examples (4-7), all showed better desorbent reaction efficiency than the conventional method, and in case of small and spherical wind-chain slag, that is, in the case of Inventive Examples (4, 7), CaC ₂ desorbent or CaO dehydration All were excellent when using the agent. In terms of the molten iron condition, the degassing rate was improved in both the molten iron and the molten iron from the blast furnace. This is because the smaller the size and the more spherical, the larger the reaction surface area of the molten iron slag is, the larger the effect of modifying the molten iron slag of the existing high viscosity and low base air.

As shown in FIG. 7, the desorbent input unit was reduced compared to the conventional unit due to the improvement of the desorbent reaction efficiency by the input of the wind-chain slag, and at the same time, it was possible to secure an equal deflow rate. In addition, the treatment time according to the reduction of the input unit of the desorbent, that is, the reduction of the blowing time, also decreased the CaO-based desorbent by 4-6 minutes, and the CaC _2- based desorbent by 2-4 minutes.

 As described above, the present invention not only increases the degassing efficiency by improving the degassing agent reaction efficiency by improving the viscosity of the molten iron slag and improving the basicity of the molten iron slag by adding the wind-chain slag before the desorbing agent, but also recycles the slag generated in the converter. As a result, the cost can be reduced by reducing the amount of waste generated and the amount of desorbent used.

Claims (4)

In the method of preliminary treatment of the molten iron of the blast furnace with topedoca, Injecting converter slag 1.0 to 2.0kg per ton of molten iron in the molten iron slag to the toppedo, Method of preliminary treatment of the molten iron for improving the degassing efficiency comprising the step of injecting a desorbing agent to the molten iron. The method of claim 1, wherein the converter slag is injected and the molten iron is bubbled for 2-3 minutes. The method according to claim 1 or 2, wherein the converter slag is a converter blow-off slag. delete

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