TW202542318A - Preheating method of cold iron source - Google Patents

Abstract

This invention provides a technique for utilizing the heat of high-temperature slag to preheat a chill source. This invention is a method for preheating a chill source, which involves feeding a portion or all of the total amount of chill source Wt (kg) into the slag that is partially or entirely retained in the reaction vessel. The ratio Wsc/Wsl (-) of the amount of residual slag in the reaction vessel to the amount of chill source Wsc (kg) fed into the reaction vessel using a waste chute is controlled within the range of the following formula (1) or (2) to satisfy the temperature Tf (°C) of the residual high-temperature material in the furnace when the slag is retained. (1) Equation 5.224× ^10⁻⁷ ×Tf ² -1.779× ^10⁻⁴ ×Tf-0.4321＜Wsc/Wsl≦8.64× ^10⁻⁷ ×Tf ^1.947 (2) Equation Wsc/Wsl≧6.591× ^10⁻⁶ ×Tf ^1.695

Description

Preheating method of cold iron source

This invention relates to a method for preheating the cold iron source by placing a chilled iron source into the slag remaining in a reaction vessel such as a converter, and utilizing the heat of the slag.

In this manual, "x~y" indicates "above x and below y", including boundary values. Furthermore, chemical formulas such as " _SiO₂ " indicate the compounds they form, and the designations of "iron" and "phosphorus" indicate the presence of the element regardless of its form. T.Fe refers to total iron content, representing the sum of iron components regardless of their form. M.Fe refers to metallic iron. The designation "M" indicates the presence of element M in molten iron. (R) indicates the presence of compounds with the chemical formula R in the slag. "Molten iron" refers to a molten metal containing iron as its main component, including: "molten iron" (molten pig iron) containing approximately 3-5% C by mass and "molten steel" containing approximately 2% C by mass or less. The unit of mass "t" represents 1000 kg.

In recent years, due to increased demands for _CO2 emission reduction, there has been a requirement to increase the use of chilled iron sources in the steelmaking process. In addition to the molten iron discharged from the blast furnace, chilled iron sources are added to the reaction vessel, thereby reducing the proportion of molten iron relative to the molten iron filling the reaction vessel and being refined (hereinafter referred to as the iron admixture). This, in turn, reduces the amount of molten iron used per unit of crude steel production.

There are various types of chills. For example, scrap iron is stored in a yard, and reduced iron fed into a furnace is accumulated in an underground bunker, which is generally managed at room temperature. These chills are loaded into the reaction vessel from a scrap chute or a furnace feed hopper. The chills are heated as they are completely melted in the molten iron, and additional heat is required until they reach a molten state.

Therefore, when using a larger quantity of chilled iron, the portion that cannot be fully compensated by the heat inherent in the molten iron itself and the combustion heat of its impurities is supplemented by adding materials that increase heat output or by external forced heating methods. Examples of materials that increase heat output include amorphous graphite and ferrosilicon alloys, and silicon carbide. Examples of heating methods include burners and electric arc discharge.

However, within the reaction vessel, impurities are removed by adding slag, which is formed on the molten iron being filled. This slag is heated to 1300-1400°C during dephosphorization and 1600-1700°C during decarburization, thus containing high calorific value. Typically, the treated slag is solidified by adding cooling materials such as dolomite, remaining within the reaction vessel while the unsolidified portion is discharged. This is because when the slag is unsolidified, the iron oxide in the slag reacts violently with the carbon in the molten iron, causing the slag to bump.

However, if the waste is preheated using the heat of the slag itself, which cannot be effectively utilized due to being discharged from the container, it can reduce the amount of heat required for heating or melting the chill. Therefore, using a chill can further reduce the iron adsorption rate compared to room temperature.

Therefore, several methods have been disclosed to prevent such sudden boiling and to preheat the cold iron source using residual slag remaining in the reaction vessel. For example, Patent 1 discloses a technique for tapping steel while the decarburized slag generated by decarburization treatment remains in the reaction vessel, and for charging a solid iron source into the residual slag. It also teaches a method for charging molten iron after charging the solid iron source, while simultaneously charging the molten iron, to satisfy the condition Wsl/Wsc‧(2-N ^- 2)＜1. In this formula, Wsc is the amount of solid iron source charged (t/ch), Wsl is the amount of residual decarburized slag (t/ch), and N is the number of times the refining vessel is repeatedly tilted.

Furthermore, Patent Document 2 discloses a method for solidifying molten iron residues, such as slag or molten iron, in the furnace after tapping steel from a converter by introducing a solid iron source.

The technology disclosed in Patent 1 aims to recover decarburized slag, while the technology disclosed in Patent 2 aims to prevent the outflow of residual molten iron from the converter during slag discharge. Although their purposes differ, both can be applied to the preheating of chilled iron sources for slag within the reaction vessel. [Prior Art Documents][Patent Documents]

Patent Document 1: Japanese Patent Application Publication No. 2004-256839; Patent Document 2: Japanese Patent Application Publication No. 2009-228102

(Problem to be Solved by the Invention) However, the aforementioned prior art still has the following problems that must be solved. That is, the technology described in Patent 1 or 2 cannot address the problem of slag boil-off that may occur when a chill containing moisture enters the high-temperature slag in the reaction vessel due to the difference in specific gravity. The chill containing moisture is, for example, water that can be unavoidably entered into the depressions of plate-shaped waste or wetted powdery waste during rainy weather.

For ease of transport, cold iron sources are typically stored in roofed but not enclosed buildings. Even in such storage, the cold iron sources cannot be completely protected from wind and rain, and must be preheated at their storage location to remove moisture. Besides requiring preheating equipment, this also defeats the purpose of utilizing heat effectively.

Furthermore, the aforementioned prior art also has problems with countermeasures to suppress the reaction with molten iron. The solid iron source loading amount Wsc in the formula disclosed in Patent 1, if intended to ensure production volume, is a value determined according to the production plan and is therefore a non-controllable parameter. This would result in either reducing the amount of residual slag Wsl or increasing the number of repeated incising cycles N. The former fails to meet the purpose of preheating the cold iron source because the total heat capacity of the slag is reduced, while the latter reduces productivity due to increased non-steelmaking time.

In Patent Document 2, the solid iron source is added to solidify the residual molten iron in the reaction vessel, and the slag is discharged from the furnace in a molten state. Therefore, the method described in Patent Document 2 cannot achieve the purpose of preheating the cold iron source using the residual slag. Although it describes how making the solid iron source less than 1 mm in size will leave solid iron source in the molten slag, it is difficult to ensure a sufficient amount of such solid iron source.

This invention was made to solve the above-mentioned problems. Its purpose is to enable the use of the heat contained in the high-temperature slag remaining in the reaction vessel for preheating the cold iron source in a safe and stable manner, without slag boil-off, and without missing the opportunity. (Technical means to solve the problem)

In view of these problems, the inventors have repeatedly and carefully studied them and found that by using the ratio of the amount of residual slag in the reaction vessel to the amount of cold iron source fed into the reaction vessel, and the temperature of the high-temperature material remaining in the furnace for treating the slag residue, the conditions that will not cause the slag to boil over can be specified.

The present invention provides a method for preheating the chill source that can help solve the above problems. This method involves preheating the chill source by adding a portion or all of the total amount of chill source Wt (kg) into the slag remaining in the reaction vessel after the refined molten iron is discharged from the reaction vessel by adding slag to the molten iron filled in the reaction vessel. The method is characterized in that the ratio Wsc/Wsl (-) of the amount of residual slag in the reaction vessel to the amount of chill source Wsc (kg) added to the reaction vessel using a waste chute is controlled within the range of the following formula (1) or (2) to satisfy the temperature Tf (°C) of the residual high-temperature material in the furnace when the slag is treated to leave the residue. (1) Equation 5.224× ^10⁻⁷ ×Tf ² -1.779× ^10⁻⁴ ×Tf-0.4321＜Wsc/Wsl≦8.64× ^10⁻⁷ ×Tf ^1.947 (2) Equation Wsc/Wsl≧6.591× ^10⁻⁶ ×Tf ^1.695

In addition, the preheating method of the chill source of the present invention is a better solution to the problem as follows: (a) a chill source that is prone to containing moisture, including powdered chill source and chill source with gaps, is arranged at position X, which is in the long side direction of the above-mentioned waste chute, and within the range of the above-mentioned formulas (1) and (2) respectively, satisfying the following formulas (3) and (4); (b) when the amount of chill source Wsc fed into the above-mentioned waste chute is a part of the total amount of chill source Wt, after the chill source is fed into the above-mentioned waste chute, the remaining chill source is fed into the furnace feed hopper. (3) Equation X≧(1.226× ^10⁻⁵ ×Tf² ^-2.589 × ^10⁻² ×Tf+17.75)×(Wsl/Wsc) (4) Equation X≧8.618× ^10⁻⁵ ×Tf + ^1.947 ×(Wsl/Wsc) Here, X (%) represents the percentage of waste accumulation position along the long side of the waste chute. The reaction vessel side at the front end of the waste chute is set to 0%, and the side opposite to the reaction vessel at the end of the waste chute is set to 100%. (Effects compared to prior art)

According to the present invention, the heat of the high-temperature slag remaining in the reaction vessel can be utilized for the preheating of the cold iron source, and there is no slag boiling. The preheating of the cold iron source can be carried out safely and without missing the opportunity.

The embodiments of the present invention will now be described in detail. Furthermore, the drawings are schematic and may differ from actual embodiments. Also, the embodiments described below are illustrative of apparatuses and methods used to embody the technical concept of the present invention, and do not constitute a limitation on the structure of the present invention as described below. That is, the technical concept of the present invention can be modified in various ways within the scope of the patent application.

Figure 1 shows the configuration of a preferred apparatus for implementing the preheating method of the chill source according to the present invention. A reaction vessel 1, such as a converter, with refractory material 2 attached to its inner surface, is tilted to discharge molten iron out of the reaction vessel 1 through the tap hole 3. Then, as shown in Figure 1(a), with some or all of the slag 4 remaining inside the reaction vessel 1, the reaction vessel 1 is tilted towards the waste chute 6 containing the chill source 5. The front end of the waste chute 6 is inserted into the reaction vessel 1. Then, a crane 7 is used to tilt the waste chute 6 and load the chill source 5 into the reaction vessel 1. There is approximately 1 ton of pre-processed molten iron, i.e., residual molten iron, inside the container.

After the chill source 5 is added, as shown in Figure 1(b), the reaction vessel 1 is tilted towards the crane 7 again. At the same time, the molten iron pot 9 is tilted to load the molten iron 10 into the reaction vessel 1. After the molten iron 10 is loaded, the reaction vessel 1 is made upright as shown in Figure 1(c). Then, while oxygen 12 is blown from the oxygen lance 11 to adhere to the molten iron 10 or slag 4, the molten iron 10 is stirred using gas blown in from the bottom blowing system 13. Next, the process moves to the refining step for the oxidation removal of impurities. Before or during the above refining step, there may also be cases where the furnace feed material 15 is added from the furnace feed hopper 14.

In addition to slag-forming materials such as lime or cooling materials such as ore, furnace chills of the size that can be rolled up to the furnace feed hopper can also be used for the material 15 fed into the furnace.

The composition of slag 4 is not particularly limited. Generally, it consists mainly of CaO, _SiO2 , and FeO, and also includes steelmaking slags such as _Al2O3 , _MgO , _P2O5 , _MnO , S, M, and Fe (metallic iron). Here, FeO refers to iron oxides, such as FeO and _Fe2O3 . The basicity (C/ _S ) represented by the mass ratio of CaO to _SiO2 in the slag is mostly 0.5 to 4.5, and the FeO concentration in the slag is mostly 3 to 40% by mass. Alternatively, slag-forming promoting materials such as _TiO2 can be added as additives 15 to lower the melting point of the slag.

The refractory 2 attached to the inner surface of the reaction vessel is made of a material that is sufficiently resistant to corrosion of the slag 4. Generally, MgO-C bricks can be used. Furthermore, in order to prevent the refractory from melting towards the slag, the processing temperature can be adjusted, or, depending on the composition of the slag 4, a MgO source such as lightly calcined dolomite can be added as a furnace feed material 15.

In addition to carbon steel scrap or molten iron scrap, the chiller source 5 can also collect granular molten iron, reduced iron, etc., which can be coiled onto the furnace feed hopper 14 and stored in the scrap chute 6. Examples of carbon steel scrap include machined iron filings, pressed iron filings, crushed iron filings, cut iron filings, and steel cutting powder. Examples of molten iron scrap include old molten iron and molten iron cutting powder. Here, cutting powder or pipe, motor, pressed iron filings, and other powdery or porous scrap are prone to containing moisture.

After the chill source 5 is loaded, the reaction vessel 1 is repeatedly tilted to mix the chill source 5 and the slag 4. Although repeated tilting of the reaction vessel 1 is not necessary, it is preferable to perform repeated tilting from the perspective of promoting the dispersion of the chill source 5 and the solidification of the slag 4.

In this embodiment, the amount of chill source 5 fed from the waste chute is determined by the temperature of the residual high-temperature material in the furnace during residual slag treatment, such as the final temperature of the residual molten iron 8, and the amount of residual slag. Thus, there is a possibility that the amount of chill source fed from the waste chute 6 may be less than the necessary total amount of chill source fed. In this case, at the point after the chill source 5 is fed from the waste chute 6, the reaction vessel 1 is uprighted, and the furnace feed hopper 14 feeds the furnace chill source as furnace feed material 15. The furnace chill source refers to granular molten iron or reduced iron, etc., that can be drawn up to the furnace feed hopper 14.

Whether before or after the start of the refining process, the chill source 5 can be added to the furnace after being fed from the scrap chute. However, if the molten iron temperature is low before refining begins, the initial drop in molten iron temperature during the refining process is greater due to the heat absorption associated with the melting of the chill source. Therefore, when the molten iron temperature drops to approximately 60°C above the molten iron solidification temperature obtained from the C-Fe binary system state diagram, the gas outlet of the furnace bottom blowing system 13 will become blocked due to molten iron solidification or the growth of the solidified phase of the chill source. In this situation, the stirring may not be effectively applied to the steel bath, leading to adverse effects such as slag over-oxidation, reduced iron yield, and decreased refining properties. Furthermore, it can cause gas to escape through the gaps in the furnace wall along the refractory material, resulting in equipment malfunctions such as refractory detachment. Therefore, it is preferable to utilize the heat of combustion of impurities in the oxygen to increase the molten iron temperature, and to introduce the aforementioned furnace chiller source after the refining process begins.

The agitating gas supply from the bottom blowing system 13, from the perspective of preventing nozzle blockage, ensures that a certain flow rate of gas is continuously circulated at a standby flow rate before the refining step. The standby flow rate is based on the amount of residual molten iron 8 and slag 4, and the diameter of the gas outlet from the bottom blowing system 13, with the standard being that the gas discharge pressure is not lower than the static pressure. The type of gas blown in from the bottom blowing system 13 is generally an inert gas, such as _N2 or Ar.

Next, the process of a preferred embodiment of the present invention will be described in detail. (First Embodiment) <Slag Boiling Confirmation Test> The first embodiment is necessary because even when the test is conducted within the scope of the suitable example of Patent 1, it still fails to stably suppress slag boiling. Therefore, it is necessary to clearly and quantitatively express the conditions that cause slag boiling. In a small high-frequency melting furnace that meets the constituent requirements of Figure 1, a CaO- _SiO2 -FetO ternary slag is melted, and its slag temperature is adjusted. Subsequently, while turning off the melting furnace power supply, a chilled iron source that has been immersed in water is added to the molten slag to confirm whether slag boiling occurs. Subsequently, using a spoon made from a graphite crucible, molten iron saturated at 1200-1300°C, which was melted in another furnace, was scooped up and loaded into the furnace from the slag.

Here, the slag composition is as follows: CaO concentration 20-50% by mass, _SiO₂ concentration 10-40% by mass, and FeO concentration 10-40% by mass. Furthermore, the slag temperature Tf' is 1200-1700℃, and the ratio Wsc' (kg) of the added chill source to the amount of melted slag Wsl' (kg), Wsc'/Wsl'(-), is in the range of 0.1-50. Additionally, the chill source is a small iron sheet with a length and width of 3-15mm, a thickness of 3-7mm, a C concentration of less than 30 ppm by mass, and an O concentration of less than 150 ppm by mass. This chill source is immersed in room temperature water for approximately 1 minute. Subsequently, before being put into the melting furnace, the water was gently drained and the chill was used for the experiment.

The results of the slag boil-off confirmation test using slag and a water-wetted chill are shown in Figure 2. In Figure 2, the symbol "●" represents the condition without slag boil-off, and the symbol "╳" represents the condition where slag boil-off occurs. The inventors observed from Figure 2 that the regions A and C where slag boil-off occurs, and the regions B1 and B2 where it does not, can be adjusted according to the ratio Wsc' (kg) of the added chill to the amount of melted slag Wsl' (kg), Wsc'/Wsl'(-), and the slag temperature Tf'.

In the slag boilover region A, where the mass of the chilled iron source relative to the residual slag is lower than Wsc'/Wsl', the slag does not boil over immediately after the chilled iron source is added, or after a period of time. The boilover is characterized by the gas generated when saturated molten iron C is subsequently added. The region B1 where this boilover does not occur can be approximated using the following formula (1A): (1A) Wsc'/Wsl'＞5.224× ^10⁻⁷ × ^Tf² -1.779× ^10⁻⁴ ×Tf-0.4321

However, when the mass of the chill source relative to the residual slag is increased to a value higher than that calculable on the right side of equation (1A), a sudden boiling, as if the slag were ejected onto the melting furnace, occurs immediately after the chill source is added, or after a period of time. It can be determined that the region C in which this sudden boiling begins can be approximated by equation (1B). Equation (1B): Wsc'/Wsl'> 8.64 × ^10⁻⁷ × Tf ^1.947

Furthermore, when the mass of the chill source relative to the residual slag is increased beyond Wsc'/Wsl', slag boil-off no longer occurs. It can be determined that this region B2 can be approximated by the following equation (2): (2) Wsc'/Wsl' ≥ 6.591 × ^10⁻⁶ × Tf ^1.695

Regarding the distinction between the aforementioned slag boilover zones A and C and the non-boiling zones B1 and B2, it has been determined that, at least within the scope of this experiment, there is no dependence on slag composition. The theory determining the critical values of the slag boilover zones A and C and the non-boiling zones B1 and B2 has not yet been clarified. The inventors believe that the boilover zone A on the lower side of Wsc’/Wsl’ is due to the relatively small amount of chilled iron input compared to the amount of slag, resulting in insufficient solidification of the slag and a vigorous reaction between the C in the molten iron and the FeO in the slag. That is, it can be presumed that the reaction [C] + (FeO) = CO↑ + Fe is a liquid-liquid reaction. Furthermore, in the sudden boiling zone C, where the mass ratio of the chill source to the residual slag is higher than Wsc’/Wsl’, there is a phenomenon where the slag is forcefully ejected upwards. From this, it can be inferred that the moisture in the waste rapidly vaporizes due to the high-temperature slag, causing a vapor explosion.

The <Molten Iron Boiling Confirmation Test> was conducted to confirm whether molten iron boiling occurred when a water-wetted chill was added to the residual molten iron in the container, in addition to slag. The results of the molten iron boiling confirmation test are shown in Figure 3. In Figure 3, the symbol "●" represents the condition without molten iron boiling, and the symbol "╳" represents the condition in which molten iron boiling occurred. Molten iron was melted in a small high-frequency melting furnace, and the temperature of the molten iron was adjusted. Then, while the furnace power was turned off, a chill immersed in water was added to the molten iron. At this time, a test was conducted to confirm whether molten iron boiling occurred. Here, the molten iron temperature Tf’’ is 1200℃~1700℃, and the ratio Wsc’’/Wrm’’(-) of the amount of chilled iron source added Wsc’’ (kg) to the amount of molten iron melted Wrm’’ (kg) is in the range of 0.1~3.0. The chilled iron source is the same material used in the above-mentioned slag boilover confirmation test.

As shown in Figure 3, the inventors have discovered that, like slag, the region D where molten iron boils suddenly and the region E where it does not boil suddenly can be sorted out according to the ratio Wsc’’/Wrm’’(-) of the molten iron temperature Tf’’ and the amount of cold iron source Wsc’’(kg) relative to the amount of molten iron Wrm’’(kg).

In region D, where molten iron spontaneously boils, it is confirmed that the molten iron spontaneously boils upwards immediately after the addition of the chill source or after a period of time. The range of the mass ratio of the chill source to the residual molten iron is significantly narrower than that of regions A and C in the slag spontaneous boiling confirmation test. Furthermore, in actual operation, the amount of residual molten iron in the reaction vessel is approximately 1 ton, while the amount of slag exceeds 10 to 20 tons. Therefore, if the amount of chill source in Figure 2 can be ensured to be above the lower limit of equation (1A), it automatically becomes the mass ratio Wsc''/Wrm'' of the chill source to the residual molten iron that can avoid the spontaneous boiling of region D in Figure 3. Therefore, even if there are both slag and residual molten iron in the reaction vessel, it will not be a problem if the following formula (1)' or (2)' representing the slag boilover avoidance zone B1, B2 can be satisfied. (1)' 5.224× ^10-7 ×Tf' ² -1.779× ^10-4 ×Tf'-0.4321＜Wsc'/Wsl'≦8.64× ^10-7 ×Tf' ^1.947 (2)'Wsc'/Wsl'≧6.591× ^10-6 ×Tf' ^1.695 .

(Second Embodiment) The second embodiment is based on the necessity that even when using a powdery or porous chill that is particularly prone to containing moisture, the need for spontaneous boiling can be avoided without problems. In a small high-frequency melting furnace that meets the requirements of Figure 1, a small amount of molten iron is melted with CaO- _SiO2 -FetO ternary slag, and the temperatures of the molten iron and slag are adjusted. Then, while turning off the power to the melting furnace, a chill that has been immersed in water is added to the molten slag to check for any spontaneous boiling of the slag. Subsequently, using a spoon made from a graphite crucible, molten iron saturated at 1200-1300°C, melted in another furnace, is scooped up and loaded from the slag into the furnace.

Here, the slag composition is as follows: CaO concentration is 20-50% by mass, _SiO₂ concentration is 10-40% by mass, FeO concentration is 10-40% by mass, and the slag and metal temperature Tf''' is 1200-1700℃. The ratio of the amount of chilled iron input Wsc''' (kg) to the amount of molten slag Wsl''' (kg), Wsc'''/Wsl'''(-), is in the range of 0.1-50. Furthermore, the ratio of the amount of chilled iron input Wsc''' (kg) to the amount of molten iron Wrm''' (kg), Wsc'''/Wrm'''(-), is in the range of 0.1-3. In addition to using small iron sheets 5A with a length and width of 3-15mm, a thickness of 3-7mm, a C concentration of less than 30 ppm, and an O concentration of less than 150 ppm, the chill source also uses pure iron sheets 5B cut to 1cm on each side with a drill bit to create multiple indentations of about 2mm depth on each side. After being immersed in room temperature water for about 1 minute, the water is gently drained before being put into the melting furnace for testing.

In the aforementioned slag boil-off confirmation test, when using a chill source that easily contains moisture, even if the total amount of chill source is in region B2 of Figure 2 where slag boil-off does not occur, slag ejection, which is considered to be caused by vapor explosion, still occurs. After careful analysis, the inventors confirmed that the change in slag boil-off region C is not due to the combined use of a chill source that easily contains moisture. That is, when the chill source is added continuously rather than all at once, the ratio of the mass of the added waste material to the residual slag, Wsc’’’/Wsl’’’, increases from region B1 of Figure 2 where slag boil-off does not occur, eventually entering region C where slag boil-off occurs. At this point, a chilled iron source that is prone to containing moisture is introduced. It is confirmed that slag ejection will occur before the chilled iron source is introduced and the mass ratio Wsc’’’/Wsl’’’ reaches the region B1 where slag boil-off has not occurred.

To verify this, as shown in Figure 4, the length of the waste chute 6 was adjusted by setting the front end position 6A of the chute to 0% and the end position 6B of the chute to 100%. Within this range, the position X (%) containing the chill source (pure iron sheet 5B) which is particularly prone to moisture accumulation was varied in various ways. Then, verification was performed using the same procedure as the slag boilover confirmation test described above.

In Figure 5, as an example, the experiment was conducted with the mass ratio of the input waste material to the residual slag when all chill sources were used, Wsc’’’/Wsl’’’, forming the slag-free boiling zone B2 on the upper side of Figure 2. At this time, the slag and molten iron temperature Tf’’’ was set to 1600℃, and the presence or absence of slag boiling is plotted in Figure 5. The symbol “●” in Figure 5 represents the condition without slag boiling, and the symbol “╳” represents the condition where slag boiling occurred. When chill sources 5, which are particularly prone to containing moisture, are used together, even if the mass ratio of the input waste material to the residual slag when all chill sources are used is Wsc’’’/Wsl’’’, which is the slag boil-off zone B2, there are cases where slag boil-off occurs and cases where it does not occur. Therefore, it can be determined that this zone can be defined by the location X of the chill source that is prone to containing moisture and the mass ratio of the input waste material to the residual slag Wsc’’’/Wsl’’’.

Figure 6 shows the critical value for slag boil-off at position X at various temperatures, based on the mass ratio of the input waste material to the residual slag (Wsc'''/Wsl'''). Here, the slag and molten iron temperatures (Tf''') are set to the range of 1200~1700℃. Furthermore, it is assumed that the mass ratio of the input waste material to the residual slag (Wsc'''/Wsl''') becomes the condition for the slag boil-off-off regions B1 and B2 (upper and lower sides of Figure 2) where no slag boil-off occurs. From the results in Figure 6, it can be determined that these critical values can be approximately calculated using the following formula. (A) When no slag boil-off zone B2 occurs on the upper side of Figure 2 (2) Equation Wsc/Wsl ≧ 6.591× ^10⁻⁶ ×Tf ^1.695 (4) Equation X ≧ 8.618× ^10⁻⁵ ×Tf ^1.947 ×(Wsl/Wsc) (B) When no slag boil-off zone B1 occurs on the lower side of Figure 2 (1) Equation 5.224× ^10⁻⁷ ×Tf ² -1.779× ^10⁻⁴ ×Tf -0.4321＜Wsc/Wsl ≦ 8.64× ^10⁻⁷ ×Tf ^1.947 (3) Equation X ≧ (1.226× ^10⁻⁵ ×Tf ²⁾ -2.589×10 ^-2 ×Tf+17.75)×(Wsl'''/Wsc''')

Since the slag temperature Tf’, molten iron temperature Tf’’, and the combined slag and molten iron temperature Tf’’’ are all defined as the temperature at which water comes into contact with a high-temperature object, they can be integrated and set as the temperature of the high-temperature object Tf (°C). In practical applications, when it is difficult to measure the temperature of the residual slag in the furnace every time, the slag temperature is almost the same as the molten iron temperature, and there is a large gap between the end of one process and the start of the next process, the slag temperature drops too much and is difficult to meet the requirements of this invention. Therefore, it is also acceptable to set the temperature of the high-temperature object Tf (°C) as the final molten iron temperature for the treatment of slag residue. However, if the cooling material is added to the residual slag before being fed into the chill source from the waste chute, it is preferable to simultaneously consider the cooling energy of the cooling material and the temperature drop predetermined by its addition amount to determine Tf, or to perform slag temperature measurement.

Wsc’, Wsc’’, Wsc’’’, Wsl’, Wsl’’, Wsl’’’, and Wrm’’ are classifications used only to distinguish different test conditions. Therefore, they all refer to the amount of chills fed into the waste chute (marked as sc), the amount of residual slag in the furnace (marked as sl), and the amount of residual molten iron in the furnace (marked as rm), and can be respectively designated as Wsc, Wsl, and Wrm.

(Third Embodiment) The third embodiment is implemented to address a situation where the amount of chills fed from the waste chute becomes less than the total amount of chills to be fed into the treatment. The reason for this is that the present invention determines the amount of chills fed from the waste chute based on the final temperature of the molten iron treated with slag residue and the amount of slag residue. Using a converter that meets the structural requirements of Figure 1, a chill source is fed from the scrap chute in a manner that satisfies both the first and second embodiments. After a refining step involving the removal of impurities by oxygen, molten iron is discharged from the converter tap hole to the take-off pot, and the slag is carried to the next processing step. The same procedure is then performed in the next processing step. In this case, if the amount of chill source Wsc fed from the scrap chute as specified in the first embodiment is insufficient relative to the total amount of chill source Wt to be added to the processing step, an insufficient amount of on-furnace chill source is fed from the on-furnace feed hopper before feeding the chill source from the scrap chute.

In the aforementioned experiments, it was confirmed that the occurrence rate of slopping increased with the number of consecutive trials. The inventors investigated the cause and discovered that, before the chill source was fed from the scrap chute, the residual molten iron and the chill source fed into the slag formed a solidified slag phase mixed with iron directly above the bottom blowout outlet, causing it to harden and block the outlet. The cause was determined to be slag peroxidation under these conditions, which was the cause of the slopping. The clogging of this bottom-blowing nozzle, as shown in Figure 7, occurs during processing when the lowest temperature Tmin (°C) reached by the molten iron in the steel bath is below 60°C, calculated from the liquidus temperature Tliq (°C) obtained from the C-Fe binary system state diagram at the C concentration Cc (mass %) in the molten iron. In Figure 7, the symbol "○" indicates the condition without nozzle clogging, and the symbol "╳" indicates the condition where nozzle clogging has occurred.

Therefore, the inventors have set the time point for adding the furnace chill source, which is added before the waste chute, to be after the waste chute has added the chill source. Specifically, the minimum temperature Tmin of the steel bath is calculated using the following formula: Tmin = Tin (°C) of the molten iron being loaded and the temperature change ΔT (°C).

Furthermore, the temperature change ΔT (°C) is obtained by calculating the Si concentration Csi (mass %), the iron admixture rate Y (%), and the temperature Tin of the molten iron being charged using the following formula. The Si concentration Csi is calculated based on the Si combustion efficiency of actual furnaces. It is set to this value when the Si concentration Csi in the molten iron, which is increased by Si sources such as FeSi, is less than 0.4% by mass, but is set to 0.4% by mass when it is above 0.4%. ΔT = {76930 × Csi - (100 - Y) × 2000} ÷ 215

Next, the liquidus temperature Tliq (°C) of the carbon concentration Cc (mass%) in the molten iron is added to the nozzle closure critical temperature Tn (°C) of 60°C: Tliq + 60°C. While considering the cooling energy (kcal/kg), the maximum amount of furnace chills Wschn (kg) to be added, which is not lower than the nozzle closure critical temperature Tn, is calculated. Furthermore, the amount of furnace chills added from the scrap chute until the start of the refining step is limited to Wschn (kg) or less. Subsequently, the amount of furnace chills added is insufficient relative to the total amount of chills Wt required after the start of the refining step.

By changing the timing of the furnace cold iron source as described above, continuous operation tests can be conducted while meeting the requirements of implementation modes 1 and 2. As a result, nozzle clogging does not occur, and slag can be reliably retained within the furnace. (Industrial Applicability)

The preheating method of the cold iron source of this invention can be applied to the blast furnace-converter process to reduce the adsorption rate of molten iron, thereby helping to reduce _CO2 emissions, which is extremely useful in industry.

1: Reaction vessel 2: Refractory 3: Taphole 4: Slag 5: Chill source 5A: Small iron sheet 5B: Pure iron sheet 6: Scrap chute 6A: (Front end of scrap chute) 6B: (End of scrap chute) 7: Crane 8: Residual molten iron 9: Iron pot 10: Molten iron 11: Oxygen lance 12: Oxygen 13: Bottom blowing system 14: Top feed hopper 15: Top charge material X: (Loading location of chill source that easily contains moisture)

Figures 1(a) to (c) are schematic conceptual diagrams illustrating the equipment configuration applicable to the preheating method of the chill source of the present invention. Figure 2 is a graph showing the results of a slag boilover confirmation test when a water-wetted chill source is added to molten slag. Figure 3 is a graph showing the results of a molten iron boilover confirmation test when a water-wetted chill source is added to molten iron. Figure 4 is a schematic side cross-sectional view showing the impact of the chill source on the loading of the scrap chute. Figure 5 is a graph showing the effect of the position X of the water-containing chill source on the scrap chute on slag boilover, under the condition that the total amount of chill source meets the conditions of region B2 in Figure 2. Figure 6 shows the relationship between the mass ratio of the chill source containing moisture at the loading position X in the scrap chute and the mass ratio of the chill source to the residual slag, and the influence of the initial temperature of the residual high-temperature material in the furnace on the critical value for whether slag boil-off occurs. Figure 7 is a graph showing the influence of the relationship between the minimum temperature of molten iron and the C concentration in the molten iron on the clogging of the bottom blowout outlet.

1: Reaction vessel

2: Refractory materials

3: Steel Outlet Hole

4: Slag

5: Cold Iron Source

6: Waste chute

7: Crane

8: Residual molten iron

9: Iron Pot

10: Molten Iron

11: Oxygen Spray Gun

12: Oxygen

13: Bottom Blowing System

14: Furnace feed hopper

15: Adding materials to the furnace

Claims (3)

A method for preheating a chill source involves, after the refined molten iron is discharged from the reaction vessel by slag formed by adding it to the molten iron filled in the reaction vessel, a portion or all of the total chill source amount Wt (kg) is added to the part or all of the residual slag in the reaction vessel for preheating the chill source; characterized in that the ratio Wsc/Wsl (kg) of the residual slag in the reaction vessel to the amount of chill source Wsc (kg) added to the reaction vessel using a waste chute is controlled within the range of either equation (1) or (2) below to satisfy the temperature Tf (°C) of the residual high-temperature material in the furnace when the slag residue is treated, whereby equation (1) is 5.224 × ^10⁻⁷. ×Tf ² -1.779×10 ^-4 ×Tf-0.4321＜Wsc/Wsl≦8.64×10 ^-7 ×Tf ^1.947 (2) Equation Wsc/Wsl≧6.591×10 ^-6 ×Tf ^1.695 . For example, in the preheating method of the chill source in claim 1, a chill source that easily contains moisture, comprising a powdered chill source and a chill source with gaps, is arranged at position X. Position X is located on the long side of the waste chute and, relative to the ranges of equations (1) and (2) above, satisfies the ranges of equations (3) and (4) below respectively; (3) X ≥ (1.226 × ^10⁻⁵ × Tf² ^- 2.589 × ^10⁻² × Tf + 17.75) × (Wsl/Wsc) (4) X ≥ 8.618 × ^10⁻⁵ × Tf ^1.947 ×(Wsl/Wsc) Here, X(%) is the percentage of the waste accumulation position in the long side direction of the waste chute, with the reaction container side at the front end of the waste chute set to 0% and the side opposite to the reaction container at the end of the waste chute set to 100%. As in the preheating method for the chill source in claim 1 or 2, where the amount of chill source Wsc fed through the waste chute is a part of the total amount of chill source Wt, the remaining chill source is fed through the furnace feed hopper after the chill source is fed through the waste chute.