Estimation method of iron oxide concentration in slag in electric furnace, and treatment method of molten iron

Abstract

To disclose a novel technique for estimating an iron oxide concentration of slag in an electric furnace when molten iron is treated in the electric furnace.SOLUTION: A method according to the present disclosure is a method for estimating an iron oxide concentration of slag in an electric furnace when molten iron is treated in an electric furnace including at least one coal feed lance, the method including generating, for the coal feed lance, a furnace yield estimation model of a carbonaceous material in the furnace, calculating an oxygen mass balance in the electric furnace using the furnace yield estimation model, and estimating the iron oxide concentration of slag in the electric furnace based on the oxygen mass balance. Here, the furnace yield estimation model includes, as a parameter, at least a distance from a nozzle injection port of the coal feed lance to a surface of the molten iron in the electric furnace.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application discloses a method for estimating the iron oxide concentration of slag in an electric furnace and a method for treating molten iron. [Background technology]

[0002] In the molten iron refining process, the iron oxide concentration in slag affects the slag's foamability and its ability to remove impurity elements from the metal. Therefore, it is important to accurately estimate the iron oxide concentration in slag. The iron oxide concentration in slag is affected by the addition of auxiliary materials such as lime, the oxidation of metal components such as Si and Mn, and the oxidation of Fe due to oxygen supply. Patent Document 1 discloses a technique for estimating the iron oxide concentration in slag from a mass balance calculation that takes into account the slag discharge in a converter furnace process. Meanwhile, unlike converter furnace processes, electric arc furnace processes often involve coal supply. Therefore, the variable in-furnace carbonaceous material yield (hereinafter sometimes referred to as "carbonaceous material efficiency") significantly affects the oxygen balance, hindering the estimation of the iron oxide concentration in slag. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-044220 Summary of the Invention [Problem to be solved by the invention]

[0004] When processing molten iron in an electric furnace, a new technique is needed to estimate the iron oxide concentration of the slag in the electric furnace. [Means for solving the problem]

[0005] The present application discloses the following aspects as one of means for solving the above problems. <Aspect 1> 1. A method for estimating iron oxide concentration in slag in an electric furnace when treating molten iron in the electric furnace, the method comprising: Creating a furnace yield estimation model of the carbonaceous material for at least one of the coal feeding lances; Calculating the oxygen mass balance in the electric furnace using the furnace yield estimation model; and estimating the iron oxide concentration of the slag in the electric furnace based on the oxygen mass balance; Including, The furnace yield estimation model includes at least The distance from the nozzle injection hole of the coal feeding lance to the surface of molten iron in the electric furnace as a parameter, A method for estimating the iron oxide concentration of slag in an electric furnace. <Aspect 2> A method for estimating an iron oxide concentration of slag in an electric furnace according to aspect 1, comprising: Creating the in-furnace yield estimation model for each of the coal sending lances; Including, A method for estimating the iron oxide concentration of slag in an electric furnace. <Aspect 3> 1. A method for treating molten iron in an electric furnace having at least one coal feed lance and at least one oxygen feed lance, comprising: Estimating the iron oxide concentration of slag in an electric furnace by the method of aspect 1 or 2; Determining one or both of the coal feeding conditions from the coal feeding lance and the oxygen feeding conditions from the oxygen feeding lance based on the estimated iron oxide concentration of the slag; and and treating the molten iron by feeding coal from the coal feeding lance or feeding oxygen from the oxygen feeding lance according to the determined conditions. How to process molten iron. [Effects of the Invention]

[0006] According to the technology of the present disclosure, when treating molten iron in an electric furnace, it is possible to estimate the iron oxide concentration of slag in the electric furnace. [Brief explanation of the drawings]

[0007] [Figure 1] 1 shows an example of the flow of a method for estimating the iron oxide concentration of slag in an electric furnace. [Figure 2] FIG. 4 is a schematic diagram for explaining the distance from the nozzle injection hole of the coal feeding lance to the surface of molten iron. [Figure 3] 1 shows an example of an oxygen mass balance. [Figure 4] 1 shows an example of the flow of a method for treating molten iron. [Figure 5] The graph shows the relationship between the nozzle-to-molten metal surface distance and the processing time. [Figure 6] The graph shows the relationship between the nozzle-molten metal surface distance and the carbon efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0008] The method for estimating the iron oxide concentration of slag in an electric furnace and the method for treating molten iron according to the present disclosure will be described below with reference to the drawings. However, the method for estimating the iron oxide concentration of slag in an electric furnace and the method for treating molten iron according to the present disclosure are not limited to the embodiments shown in the drawings.

[0009] 1. Method for estimating iron oxide concentration in slag in electric furnaces 1 shows an example of a flow chart of a method for estimating the iron oxide concentration of slag in an electric furnace when treating molten iron in the electric furnace having at least one coal feeding lance. As shown in FIG. 1, the method includes: S1: Creating a furnace yield estimation model of carbonaceous material for at least one of the coal feeding lances; S2: Calculating the oxygen mass balance in the electric furnace using the furnace yield estimation model; and S3: Estimating the iron oxide concentration of slag in an electric furnace based on oxygen mass balance; In this embodiment, the furnace yield estimation model includes at least The distance from the nozzle of the coal lance to the surface of the molten iron in the electric furnace. as a parameter.

[0010] When carbonaceous materials are injected onto the surface of molten iron in an electric furnace, the degree of scattering of the carbonaceous materials and the amount of carbonaceous materials trapped in the molten iron vary depending on the distance from the nozzle injection hole of the coal feed lance to the surface of the molten iron. For example, the longer the distance from the nozzle injection hole of the coal feed lance to the surface of the molten iron, the longer the scattering distance of the carbonaceous materials and the smaller the amount of carbonaceous materials trapped in the molten iron, making the carbonaceous materials more likely to be burned and consumed in the gas phase within the electric furnace. Therefore, in order to accurately estimate the in-furnace yield of carbonaceous materials, it is effective to consider the distance from the nozzle injection hole of the coal feed lance to the surface of the molten iron. By accurately estimating the in-furnace yield of carbonaceous materials, the oxygen mass balance within the electric furnace can be accurately calculated. By accurately calculating the oxygen mass balance within the electric furnace, the iron oxide concentration of the slag within the electric furnace can be accurately estimated. Accurate estimation of the iron oxide concentration of slag in an electric furnace enables appropriate coal and oxygen supply according to the estimated oxygen concentration of the slag, making it easier to properly remove impurities such as P contained in molten iron and to stabilize the foaming state of the slag.

[0011] 1.1 S1 In S1, an in-furnace yield estimation model of carbonaceous material is created for at least one of the coal feed lances provided in the electric furnace. In particular, by creating an in-furnace yield estimation model for each of the coal feed lances in S1 (if multiple coal feed lances are provided, an in-furnace yield estimation model is created for all of the coal feed lances), it is possible to more accurately estimate the iron oxide concentration of slag in the electric furnace when treating molten iron in the electric furnace. The in-furnace yield estimation model includes at least the distance from the nozzle injection hole of the coal feed lance to the surface of molten iron in the electric furnace as a parameter.

[0012] The "furnace yield of carbonaceous material" refers to the percentage of carbonaceous material injected from the coal feed lance that reacts with slag, metal, and the oxygen-containing gas in the furnace without leaving the dust collection system unreacted or reacting with oxygen in the air. The "furnace yield of carbonaceous material estimation model" refers to a model for estimating the furnace yield of carbonaceous material. The furnace yield of carbonaceous material estimation model may be, for example, a mathematical expression of the furnace yield of carbonaceous material using parameters including the distance from the nozzle injection hole of the coal feed lance to the surface of the molten iron in the electric furnace. That is, in this embodiment, focusing on the fact that the degree of scattering of carbonaceous material and the amount of carbonaceous material captured by the molten iron change depending on the distance from the nozzle injection hole of the coal feed lance to the surface of the molten iron, and therefore the furnace yield of carbonaceous material changes, the furnace yield of carbonaceous material is created by taking at least this distance into consideration. The "distance from the nozzle injection hole of the coal supply lance to the surface of the molten iron" refers to the distance x from the center (centroid) of the nozzle injection hole 10a to the surface 20a of the molten iron 20 in the electric furnace in the injection direction of the carbonaceous material from the coal supply lance 10 (the direction along the nozzle axis A), as shown in Figure 2.

[0013] In an electric furnace, the amount of carbonaceous material injected from the coal feed lance that reacts with the slag, metal, and oxygen-containing gas in the furnace and does not escape unreacted into the dust collection system or react with oxygen in the air (effective carbonaceous material amount) y can be expressed, for example, as shown in the following equation (1) using the furnace yield γ of the carbonaceous material injected from the coal feed lance. y=γ / 100×α×β / 100 (1) y: Effective carbonaceous material amount [ton] γ: Furnace yield of carbonaceous material [%] α: Amount of coal sent [ton] β: Carbon concentration in carbonaceous material (fixed carbon concentration) [mass%]

[0014] Assuming that the entire amount of carbonaceous material injected from the coal feed lance reaches the molten iron surface without being consumed by combustion, the effective carbonaceous material amount y can be calculated as α × β / 100. However, as described above, a portion of the carbonaceous material injected from the coal feed lance may be consumed in the gas phase by combustion. Therefore, when the effective carbonaceous material amount y is calculated based on the formula y = α × β / 100, a discrepancy occurs between the iron oxide concentration in the slag (estimated concentration) estimated based on the calculation result and the iron oxide concentration in the slag actually determined by analysis (analyzed concentration). In contrast, in this embodiment, the in-furnace yield γ of the carbonaceous material is accurately estimated, and the effective carbonaceous material amount y is accurately estimated using the estimated in-furnace yield γ of the carbonaceous material. In other words, the in-furnace yield γ of the carbonaceous material can be considered a correction coefficient for bringing the estimated concentration of iron oxide in the slag closer to the analyzed concentration.

[0015] In this embodiment, the in-furnace yield γ of carbonaceous materials is estimated taking into account the distance x from the nozzle injection hole of the coal feeding lance to the surface of molten iron in the electric furnace. The estimation model of the in-furnace yield γ of carbonaceous materials may be expressed as a function of the distance x, for example. For example, the relationship between the in-furnace yield γ of carbonaceous materials and the distance x can be expressed as a mathematical formula based on experiments, past operational results, simulations, etc. The function of the in-furnace yield γ of carbonaceous materials and the distance x may be determined by an appropriate method such as linear regression or nonlinear regression. Furthermore, the function of the in-furnace yield γ of carbonaceous materials and the distance x may be determined using machine learning, etc.

[0016] When treating molten iron in an electric furnace, the molten iron level (height from the furnace bottom to the molten iron surface) may fluctuate during the treatment due to factors such as the supply of an iron source. That is, the distance x from the nozzle injection hole of the coal delivery lance to the surface of the molten iron in the electric furnace may also fluctuate during the treatment, regardless of the type of coal delivery lance. Therefore, the yield of carbonaceous materials may fluctuate during the treatment. In this embodiment, by estimating the in-furnace yield γ of carbonaceous materials in consideration of the distance x from the nozzle injection hole of the coal delivery lance to the surface of the molten iron in the electric furnace, even if the molten iron level fluctuates, the in-furnace yield γ of carbonaceous materials can be accurately estimated according to the distance x after the fluctuating value.

[0017] 1.2 S2 In S2, the oxygen mass balance in the electric furnace is calculated using the in-furnace yield estimation model created in S1. The calculation method of the oxygen mass balance may be the same as the conventional method, except that the in-furnace yield γ of the carbonaceous material estimated using the in-furnace yield estimation model of the carbonaceous material is taken into consideration.

[0018] For example, an oxygen mass balance such as that shown in Fig. 3 can be used. That is, the oxygen input consisting of the oxygen supply and the solid oxygen source can be considered to be the oxygen used in the combustion of non-ferrous components, the oxygen used in the CO reaction, and the oxygen used in the secondary combustion, and the remainder can be considered to be used in the production of iron oxide (a negative value indicates a reduction reaction).

[0019] The oxygen supply source in the oxygen input shown in Figure 3 is oxygen supplied from an oxygen supply lance. When carbonaceous materials or auxiliary materials are blown into the furnace using an oxygen-containing gas as a carrier gas, the oxygen in the carrier gas is also included in the oxygen supply source. The solid oxygen source is oxygen derived from lower oxides such as iron oxide contained in the raw materials added during the treatment of molten iron.

[0020] Of the oxygen outputs shown in Figure 3, the oxygen consumed by the combustion of non-ferrous components is the oxygen consumed in reactions with non-ferrous components other than carbon contained in the iron source, and can be calculated depending on the composition of the iron source. Examples of the non-ferrous components include Si, Mn, P, and Al. Depending on the composition of the iron source, Cr, Ti, Mo, etc. may also be taken into consideration.

[0021] Of the oxygen output shown in Figure 3, the oxygen consumed by the CO reaction can be calculated based on the reaction equation C + 1 / 2O2 ⇒ CO. Here, the C in this reaction equation can be determined by subtracting the C added to the molten iron from the sum of the C in the effective carbonaceous material injected from the coal delivery lance and the C contained in the iron source (such as pig iron). The C added to the molten iron can be calculated from the weight of the molten iron and the change in carbon concentration Δ [%C] in the molten iron. Here, the effective amount of carbonaceous material y injected from the coal delivery lance can be estimated, for example, according to the above equation (1), taking into account the in-furnace yield γ of carbonaceous material estimated based on the in-furnace yield estimation model of carbonaceous material created in S1 above. That is, in this embodiment, the in-furnace yield γ of the carbonaceous material injected from the coal feed lance is accurately estimated, the effective carbonaceous material amount y injected from the coal feed lance is accurately estimated based on the estimated in-furnace yield γ of the carbonaceous material, and the amount of oxygen consumed by the CO reaction is calculated based on the estimated effective carbonaceous material amount y, thereby improving the calculation accuracy of the oxygen material balance.

[0022] Of the oxygen output shown in Figure 3, the oxygen consumed by secondary combustion can be calculated based on the proportion of CO2 that is converted into CO2 through secondary combustion (secondary combustion rate) out of the above C. The secondary combustion rate can be calculated, for example, by the following method (a) or (b). (a) Calculation of secondary combustion rate by exhaust gas analysis -Analyze CO, CO2, Ar and N2 in the exhaust gas collected from the furnace hood. -Measure the total flow rate of exhaust gas. - Estimate or measure the amount of air entering through the furnace opening. Since N2 comes from the air unless it is actively supplied, the amount of invading air is estimated from the N2 in the exhaust gas and the total flow rate. The CO2 / (CO+CO2) ratio, minus the combustion by oxygen in the air at the furnace top, is the secondary combustion rate in the furnace. (b) Calculation of secondary combustion rate based on cavity depth The cavity depth formed in the metal bath by the oxygen jet is, for example, dv0=α(L+h)×L 0.5 Here, d is the lance nozzle diameter (mm), v0 is the gas injection velocity at the lance nozzle outlet (m / s), α is a constant (for example, 0.73 is used as the experimental value), L is the cavity depth (mm), and h is the lance height (mm). The cavity depth can be calculated from the operating condition settings using the above formula. It is known that there is a correlation between cavity depth and secondary combustion rate (e.g., Toshiya Harada et al., "187 Development of Technology for Promoting Secondary Combustion in Converters: Research on Secondary Combustion in Converters (I) (Converter Gas Recovery, Equipment, Combined Blowing, Converter Refining, Stainless Steel, Secondary Combustion, Steelmaking, 109th Lecture Meeting of the Iron and Steel Institute of Japan)," Iron and Steel: 71 (1985), p. 187). Therefore, even if exhaust gas analysis equipment is not available, batch measurements can be performed to create a correlation equation, which can be used as an alternative to estimating secondary combustion rate using exhaust gas analysis. This correlation equation can be, for example, a simple regression equation for cavity depth, or a multiple regression equation or nonlinear machine learning model that includes explanatory variables such as [%C] and furnace inner diameter.

[0023] 1.3 S3 In S3, the iron oxide concentration of the slag in the electric furnace is estimated based on the oxygen mass balance calculated in S2. That is, in S2, the amount of iron oxide produced is calculated based on the oxygen mass balance as described above, while in S3, the iron oxide concentration of the slag can be estimated based on the amount of iron oxide produced. Here, in the oxygen mass balance of S2, the effective carbonaceous material amount y is taken into account as the oxygen output. As described above, the effective carbonaceous material amount y can be calculated taking into account the in-furnace carbonaceous material yield γ. As described above, the in-furnace carbonaceous material yield γ can be accurately estimated taking into account the distance x from the nozzle injection hole of the coal delivery lance to the surface of molten iron in the electric furnace. That is, according to the method of this embodiment, the effective amount y of carbonaceous materials injected from the coal feeding lance can be accurately estimated based on an in-furnace yield estimation model of the carbonaceous materials injected from the coal feeding lance, the oxygen mass balance in the electric furnace can be calculated based on the estimated effective amount y, the amount of iron oxide produced can be accurately calculated, and the iron oxide concentration of the slag can be accurately estimated based on the calculated amount of iron oxide produced. Note that in the method of this embodiment, other components contained in the slag and components contained in the molten iron may be estimated based on the iron oxide concentration of the slag estimated as described above.

[0024] 1.4 Other matters In the above explanation, the technical significance of adopting the distance x from the nozzle injection hole of the coal feeding lance to the surface of the molten iron in the electric furnace as a parameter when creating the in-furnace yield estimation model of the carbonaceous material in S1 has been shown, but in this embodiment, other parameters may be adopted in addition to this.

[0025] 1.4.1 Lance type and installation location In this embodiment, a carbonaceous material in-furnace yield estimation model is created for at least one of the coal feed lances provided in the electric furnace, thereby enabling the carbonaceous material in-furnace yield γ to be estimated with high accuracy. Here, the fixed lance and the movable lance have different positional relationships with the molten iron surface. Furthermore, in the case of a movable lance, the lance position can be freely changed within the movable range of the equipment, and therefore the relationship between the lance and the distance to the molten iron surface is different from that of a fixed lance. Furthermore, even between fixed lances, the composition and flow of furnace gas differ depending on the installation position, and therefore the carbonaceous material in-furnace yield γ also differs. In this regard, when an electric furnace has multiple coal feed lances, it is preferable to create a carbonaceous material in-furnace yield estimation model for each of the coal feed lances. This allows information regarding the type and installation location of the lance to be taken into account, thereby enabling the carbonaceous material in-furnace yield γ to be estimated with higher accuracy.

[0026] 1.4.2 Slag Information In this embodiment, the in-furnace yield estimation model may include the weight of the slag in the electric furnace as a parameter. In this embodiment, the in-furnace yield estimation model may include the forming conditions of the slag in the electric furnace (for example, the distance from the nozzle injection hole to the slag surface) as a parameter. In this way, the parameters of the in-furnace yield estimation model of the carbonaceous material include information about the slag in the electric furnace, so that the in-furnace yield γ of the carbonaceous material can be estimated with greater accuracy.

[0027] 2. Methods for treating molten iron The technology of the present disclosure also has an aspect as a method for treating molten iron. That is, the method for treating molten iron according to one embodiment is a method for treating molten iron in an electric furnace equipped with at least one coal feeding lance and at least one oxygen feeding lance, and as shown in FIG. S11: Estimating the iron oxide concentration of the slag in the electric furnace by the method of the present disclosure; S12: Determining one or both of the coal feeding conditions from the coal feeding lance and the oxygen feeding conditions from the oxygen feeding lance based on the estimated iron oxide concentration of the slag; and S13: Treating the molten iron by feeding coal from the coal feeding lance or feeding oxygen from the oxygen feeding lance according to the determined conditions.

[0028] 2.1 S11 In S11, the iron oxide concentration of the slag in the electric furnace is estimated through the above-mentioned S1 to S3. The estimation of the iron oxide concentration of the slag in the electric furnace is as described above, and a description thereof will be omitted here.

[0029] 2.2 S12 In S12, one or both of the coal feeding conditions from the coal feeding lance and the oxygen feeding conditions from the oxygen feeding lance are determined based on the estimated iron oxide concentration of the slag. For example, the amount of carbonaceous material, gas flow rate, gas flow velocity, injection angle, etc. from the coal feeding lance may be determined based on the iron oxide concentration of the slag estimated in S11 so that the iron oxide concentration of the slag becomes a target value. Also, the amount of oxygen fed from the oxygen feeding lance, oxygen flow rate, injection angle, etc. may be determined. The iron oxide concentration of the slag affects the refining capacity of the slag and the ease of foaming during slag foaming. In other words, by accurately estimating the iron oxide concentration of the slag in S11, optimal refining conditions and foaming conditions corresponding to the iron oxide concentration of the slag are determined in S12, and the coal feeding conditions and oxygen feeding conditions that can achieve the optimal refining conditions and foaming conditions can be determined.

[0030] 2.3 S13 In S13, the molten iron is treated by feeding coal from the coal feeding lance or feeding oxygen from the oxygen feeding lance according to the conditions determined in S12. This makes it possible to, for example, properly foam slag and dephosphorize the molten iron while bringing the iron oxide concentration in the slag closer to a target value.

[0031] 3. Supplementary Information 3.1 Molten iron In this embodiment, the molten iron to be processed is obtained, for example, by generating an arc in an electric furnace to melt an iron source. The iron source may include at least one selected from scrap, reduced iron, pig iron, and granulated pig iron, and may also include molten iron or molten steel produced in another melting furnace or refining furnace. The molten iron may include various elements other than iron. The composition of the elements other than iron depends on the type of iron source. For example, the molten iron before the carbonaceous material is supplied may contain 0.02% by mass to 3.0% by mass of C, 0.005% by mass to 0.030% by mass of N, and 0.003% by mass to 0.1% by mass of P. The density of the molten iron is, for example, 6,600 kg / m 3 More than 7,000kg / m 3 It may be the following:

[0032] 3.2 Coal feeding lance In this embodiment, the electric furnace includes at least one coal delivery lance. The coal delivery lance injects the carbonaceous material together with a carrier gas. The carrier gas may be one commonly used for gas transportation of powder. For example, from the viewpoint of cost, it is preferable to use one or both of air and N2 gas. From the viewpoint of nitrogen reduction, it is preferable to use at least one gas selected from pure oxygen, Ar gas, and CO2 gas. Furthermore, to prevent the carbonaceous material from being consumed in the gas phase before reaching the molten iron surface, it is preferable to use one or both of Ar gas and CO2 gas, which have lower reactivity. Thus, the carrier gas may be selected according to the production conditions, or may be a mixture of at least two or more gases in a predetermined ratio within the range of these operational constraints. The coal delivery lance may be at least one of a lance inserted from the furnace roof of the electric furnace (a so-called main lance), a wall lance provided on the furnace wall, and a variable lance positioned by a manipulator or the like. The carbonaceous material may be injected vertically downward or obliquely downward from the coal delivery lance. There is no particular limitation on the amount of carbonaceous material injected from the coal feeding lance. For example, the amount of carbonaceous material injected from one coal feeding lance may be 10 kg / min or more and 100 kg / min or less.

[0033] 3.3 Charcoal material The shape of the carbonaceous material may be any shape, such as powder, granules, or lumps, as long as it can be appropriately injected from the coal supply lance. The carbonaceous material may be selected from any carbonaceous material, such as bituminous coal, anthracite, coke breeze, pitch coke, or biomass-based carbonaceous material. The carbonaceous material may be a pressure-molded product or a mixture of multiple types of carbonaceous material. The carbonaceous material may have a particle size of, for example, 0.1 mm to 5 mm. Large carbonaceous material may easily clog the powder transport system of a typical steelmaking facility, and its small specific surface area may reduce heat transfer, resulting in a longer residence time above the molten iron as unmelted material. On the other hand, small carbonaceous material tends to scatter easily within the furnace and be easily sucked into the exhaust gas system, potentially resulting in a lower yield. Considering the injection performance from the coal supply lance, it is preferable to use a carbonaceous material containing 90% by mass or more of powder with a particle size of 0.1 mm to 3 mm.

[0034] 3.4 Oxygen supply lance An electric furnace has at least one oxygen supply lance. The oxygen supply lance injects an oxygen jet into the molten iron in the electric furnace. The number of oxygen jets injected from one lance is not particularly limited. The oxygen supply lance may be a single-hole lance. The oxygen supply lance may also be straight, have a Laval structure, or be equipped with a coherent burner that injects gaseous fuel and combustion-supporting gas so as to surround the oxygen jet. The oxygen supply lance may be at least one of a lance inserted from the furnace roof of the electric furnace (a so-called main lance), a wall lance provided on the furnace wall, and an adjustable lance positioned by a manipulator or the like. The shape of the oxygen jet injected from the oxygen supply lance depends on the inclination of the oxygen supply lance, the shape of the injection hole of the oxygen supply lance, etc. The flow rate of the oxygen jet injected from one oxygen supply lance is not particularly limited, and may be, for example, 1,000 Nm 3 / h or more 4,000Nm 3The flow velocity of the oxygen jet injected from the oxygen supply lance (the flow velocity at the injection hole of the oxygen supply lance, that is, the flow velocity at the central axis) is not particularly limited, and may be, for example, 10 m / s or more and 300 m / s or less.

[0035] 3.5 Other configurations of electric furnaces In addition to the above-mentioned coal feed lance and oxygen feed lance, an electric furnace has the obvious components of an electric furnace. For example, an electric furnace has a melting furnace for melting an iron source. The melting furnace may be defined by a furnace lid, an inner wall, and a furnace bottom. The planar shape of the melting furnace is not particularly limited. Furthermore, the bath depth of the melting furnace may change depending on the melting of the iron source. The bath depth and diameter of the melting furnace are not particularly limited. The electric furnace may be of a direct current type or an alternating current type. In the case of a direct current type, the electric furnace has at least one upper electrode and at least one lower electrode. The positions of the upper electrode and the lower electrode are not particularly limited. For example, if the molten metal surface shape in the melting furnace is approximately circular when viewed from above (plan view), the center of the circle may coincide with the central axis of one upper electrode or one lower electrode. Alternatively, multiple upper electrodes or multiple lower electrodes may be arranged around the center of the circle when viewed from above. In an electric furnace, power is supplied from a power supply unit to an upper electrode and a lower electrode, generating an arc between the upper electrode and the lower electrode. A general power supply unit may be used to supply power to the upper electrode and the lower electrode. The power supplied from the power supply unit to the electrodes is not particularly limited as long as it can generate an arc between the electrodes. The electric furnace may also be equipped with an iron source charging means for charging an iron source into the melting furnace. The electric furnace may also be equipped with a slag removal door for discharging slag and the like formed on the surface of the molten iron. The electric furnace may also be equipped with a tapping port for discharging the molten iron or molten steel. [Example]

[0036] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention allows various conditions to be adopted as long as the object is achieved without departing from the gist of the present invention.

[0037] The maximum molten iron capacity was 200 tons, and the furnace was equipped with one lance fixed to the furnace wall and one movable lance inserted through the slag removal door, each of which further had an oxygen supply lance and a coal supply lance. Molten iron was treated using conventional methods in a three-phase AC electric furnace.

[0038] 1. Creation of an estimation model for the in-furnace yield of carbonaceous material (carbonaceous material efficiency) Coal was fed into the electric furnace while changing the height of the molten iron surface, and slag and molten iron were sampled before and after feeding. The amount of iron oxide produced was estimated using mass balance calculations, and this was compared with the actual amount of iron oxide produced, creating a model to estimate the in-furnace carbon yield (carbon efficiency).

[0039] Oxygen and coal are supplied from one location each, with a supply volume of 3,000 Nm 3 The flow rate was 60 kg / min / h, and the coal feeding lance used was changed as appropriate. During operation, the supply of the main raw material (iron source) was stopped when the molten metal level reached a predetermined height, and oxygen feeding and coal feeding were carried out under constant conditions for 5 minutes. Slag and metal samples were taken before and after oxygen feeding and coal feeding and were subjected to component analysis.

[0040] The effective amount of carbonaceous material reaching the surface of molten iron from the coal supply lance can be calculated by the above formula (1).

[0041] Based on the effective carbonaceous material amount calculated in this way, the amount of oxygen consumed for iron oxide production is calculated to obtain a calculated value, and the amount of oxygen actually consumed for iron oxide production (analytical value) is measured by analysis. When the calculated value and the analytical value are equal, γ corresponds to the carbonaceous material efficiency to be estimated.

[0042] The amount of oxygen used to produce iron oxide (calculated value) is determined by comparing the oxygen input and oxygen output, taking into consideration the oxygen mass balance shown in Figure 3. The method for determining the calculated value is as described in the embodiment.

[0043] On the other hand, the amount of oxygen actually consumed in the production of iron oxide (analytical value) can be determined according to the following formula. Amount of oxygen = (C2 / 100 × W2 - C1 / 100 × W1) × M O / M FeO C1: Iron oxide concentration in slag before carbonaceous material supply [mass%] W1: Slag weight before carbon material supply [ton] C2: Iron oxide concentration in slag after carbonaceous material supply [mass%] W2: Slag weight after carbon material supply [ton] M O :Oxygen atomic weight M FeO : Molecular weight of iron oxide As the iron oxide molecular weight, for example, the molecular weight of FeO may be used.

[0044] Figure 5 shows an example of the relationship between the molten iron processing time t and the distance x from the nozzle injection hole of the coal feed lance to the molten iron surface. The distance x was determined using the installation position and injection angle of the coal feed lance as well as the molten iron surface height. The molten iron surface height can be determined, for example, from the relationship between the height and internal volume calculated from the furnace interior shape with refractories installed, and the weight of the raw materials charged into the furnace. Figure 6 also shows an example of the relationship between the distance x from the nozzle injection hole of the coal feed lance to the molten iron surface and the carbonaceous material efficiency γ. As shown in Figures 5 and 6, it can be seen that as the distance x from the nozzle injection hole of the coal feed lance to the molten iron surface changes, the carbonaceous material efficiency γ also changes. In this example, as shown in Figure 6, a polynomial approximation was calculated for the relationship between the carbonaceous material efficiency γ and the distance x, and this was used as a model for estimating the carbonaceous material retention in the furnace.

[0045] 2. Estimation of iron oxide concentration in slag using an estimation model of carbonaceous material in-furnace yield (carbonaceous material efficiency) 2.1 Experimental conditions 2.1.1 Examples 1-1 and 1-2 For one of the multiple coal feed lances installed in the furnace, a carbonaceous material in-furnace retention estimation model was created using the distance x from the nozzle injection hole of the coal feed lance to the molten iron surface as a parameter. The remaining coal feed lances were also considered to follow the carbonaceous material in-furnace retention estimation model.

[0046] In an electric furnace, carbonaceous material was supplied from a coal supply lance to the molten metal surface at an arbitrary height. For one coal supply lance, the effective amount of carbonaceous material from the coal supply lance was estimated based on the above-mentioned model for estimating the furnace yield of carbonaceous material. The remaining coal supply lances were also assumed to follow the above-mentioned model for estimating the furnace yield of carbonaceous material. An oxygen mass balance calculation was performed from the effective amount of carbonaceous material to estimate the iron oxide concentration of the slag, and the estimated value of the iron oxide concentration of the slag was compared with the measured value of the iron oxide concentration of the slag. The oxygen supply and coal supply were 1,000 to 4,000 Nm 3 The oxygen and coal feed conditions were the same and two charge tests were conducted under the same conditions.

[0047] 2.1.2 Examples 2-1 and 2-2 The estimated value of the iron oxide concentration of the slag was compared with the actual measured value of the iron oxide concentration of the slag in the same manner as in Example 1, except that a model for estimating the in-furnace yield of carbonaceous material was created for each of the coal feed lances (all of the multiple coal feed lances) installed in the furnace.

[0048] 2.1.9 Comparative Example The estimated value of the iron oxide concentration of the slag was compared with the actually measured value of the iron oxide concentration of the slag in the same manner as in Example 1, except that no model for estimating the furnace yield of the carbonaceous material was created and the iron oxide concentration of the slag was estimated assuming that 100% of the carbonaceous material from the coal feed lance reaches the surface of the molten iron.

[0049] 2.2 Evaluation indicators The following three-level evaluation was performed according to the difference (Δ%FeO) between the estimated iron oxide concentration of the slag and the measured iron oxide concentration of the slag. ×: 10%<Δ%FeO ○: 5%<Δ%FeO≦10% ◎: Δ%FeO≦5%

[0050] 2.3 Evaluation results The evaluation results are shown in Table 1 below. [Table 1]

[0051] From the above results, when treating molten iron in an electric furnace equipped with at least one coal feeding lance, the iron oxide concentration of the slag in the electric furnace can be estimated as follows: Creating a furnace yield estimation model of the carbonaceous material for at least one of the coal feeding lances; Calculating the oxygen mass balance in the electric furnace using the furnace yield estimation model; The iron oxide concentration of the slag in the electric furnace is estimated based on the oxygen mass balance. It is effective to use the above method, and it can be said that the iron oxide concentration of the slag can be estimated with high accuracy, especially when the in-furnace yield estimation model includes at least the distance from the nozzle injection hole of the coal delivery lance to the surface of the molten iron in the electric furnace as a parameter (Examples 1-1, 1-2, 2-1, and 2-2). In particular, it can be said that the iron oxide concentration of the slag can be estimated with high accuracy when the in-furnace yield estimation model is created for each of the coal delivery lances (all of the coal delivery lances) provided in the electric furnace (Examples 2-1 and 2-2). [Explanation of symbols]

[0052] 10 Coal sending lance 10a Nozzle injection hole 20 Molten Iron 20a Molten iron surface

Claims

1. 1. A method for estimating an iron oxide concentration of slag in an electric furnace when treating molten iron in the electric furnace, the method comprising: Creating an in-furnace carbonaceous material retention estimation model for at least one of the coal feeding lances; Calculating the oxygen mass balance in the electric furnace using the furnace yield estimation model; and estimating the iron oxide concentration of the slag in the electric furnace based on the oxygen mass balance; Including, The furnace yield estimation model includes at least The distance from the nozzle injection hole of the coal feeding lance to the surface of molten iron in the electric furnace as a parameter, A method for estimating the iron oxide concentration of slag in an electric furnace.

2. 2. A method for estimating the iron oxide concentration of slag in an electric furnace according to claim 1, comprising: Creating the in-furnace yield estimation model for each of the coal sending lances; Including, A method for estimating the iron oxide concentration of slag in an electric furnace.

3. 1. A method for treating molten iron in an electric furnace having at least one coal feed lance and at least one oxygen feed lance, comprising: Estimating the iron oxide concentration of slag in an electric furnace by the method according to claim 1 or 2; Determining one or both of the coal feeding conditions from the coal feeding lance and the oxygen feeding conditions from the oxygen feeding lance based on the estimated iron oxide concentration of the slag; and and treating the molten iron by feeding coal from the coal feeding lance or feeding oxygen from the oxygen feeding lance according to the determined conditions. How to process molten iron.

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