The present disclosure relates to a charcoal-adding material for efficiently performing charcoal-charging in an electric furnace or a ladle, and a charcoal-charging method using the same.
Background technology
[0002]
Conventionally, cold iron sources such as iron scrap, cold pig iron, and direct reduced iron are melted and refined in an electric furnace to produce steel materials used for building materials. The main energy source of this electric furnace is arc heat, but for the purpose of promoting melting and refining and saving expensive electric energy, oxygen gas (for oxidative melting of iron), gaseous fuel, liquid fuel, powdered coke, etc. Auxiliary heat sources are also used.
[0003]
In addition, a solid carbon material is added to the molten iron as a charcoal material to carbonize the molten iron, and the carbon in the molten iron is burned with oxygen gas to serve as an auxiliary heat source. As the carbonizing material, artificial graphite, earthy graphite, various cokes, anthracite, wood, and materials produced from these materials have been used. In the melt reduction method, a large amount of coal is generally added together with iron ore and oxidizing gas to reduce the iron ore, but auxiliary coal addition may be performed to produce high carbon steel in a ladle. be.
[0004]
As a charcoal-making material or a charcoal-making technique thereof, for example, Patent Document 1 discloses iron-making and a charcoal-making material for steelmaking obtained by firing earth-like graphite having an ash content of less than 12% by mass. No. 2 discloses a charcoal-adding technique characterized by adding earth-like graphite. Patent Document 3 discloses a charcoal-added material obtained by carbonizing coconut palm or oil palm palm gala as an alternative to coke. Further, Patent Document 4 discloses a technique for adding a carbon source derived from biomass as a carbon addition technique during the dephosphorization treatment.
[0005]
When iron scrap is used as a cold iron source in an electric furnace, it is common to perform carbon injection and oxygen enrichment operations, and the carbonized material is transported to the blowing gas and blown into the molten iron. On the other hand, if the carbonized material can be charged by free fall from above the furnace, equipment related to gas transfer can be omitted, restrictions on the particle size of the carbonized material and the like are relaxed, and the cost is reduced. In addition, when direct reduced iron is used as a cold iron source other than iron scrap, and when low-grade directly reduced iron with a low metallization rate is used, it is used for reduction in addition to the carbon source as a heat source. A carbon source is also required, and a large amount of carbon is required. Further, in order to produce low N high-grade steel, it is necessary to add coal in order to perform de-N at the time of decarburization, and if it can be charcoalized inexpensively and efficiently, the high-grade steel should be manufactured at low cost. Can be done.
[0006]
Generally, if an inexpensive carbon material containing a large amount of ash can be used, the cost can be kept low, but if the ash content in the carbon material is high, it is not preferable in many usage methods. It is generally known that when the ash content is high, the coal charging rate becomes significantly slower. Here, the carbon addition rate means the rate at which the carbon concentration in the molten iron rises when the carbon source is added into the furnace. For example, in Patent Document 1, soil graphite having an ash content of less than 12% by mass realizes a charcoalizing property (charcoalizing rate) equivalent to that of artificial graphite, but a charcoalizing material having an ash content exceeding that is added. It has been shown that the coal rate is significantly slowed down. Further, Patent Document 4 shows that the higher the ash content is, the lower the coal charging rate is, and the carbonized material has an ash content of 9% by mass or less. It is considered that the reason why the carbonization rate becomes slow when the ash content is high is that the component produced from the ash coats the carbonaceous material.
[0007]
On the other hand, a carbonizing material in which an additive is added to a carbon material, or a carbonizing method using the same has also been proposed. For example, Patent Document 5 discloses an ingot mass anthracite obtained by adding CaF 2 and MgO to powdered anthracite to form a briquette. However, at present, due to problems such as the elution of fluorine from slag, a fluorine-less material is required as an auxiliary material, and its use is restricted. Further, Patent Document 6 discloses a carbonized material in which CaO is mixed in an amount of 20% by mass or more and less than 80% by mass, but the ratio of CaO is large, so that the cost is high. Further, Patent Document 7 discloses an adjustment method in which the mass ratio of CaO / C is adjusted to be 18 or more during the RH type vacuum degassing treatment, and the carbon dioxide material is top-blown added. The method also has the problem that the ratio of CaO is large, and the increase in carbon concentration in the molten steel is in the range of 0.005 to 0.010% by mass, which is significantly different from the production of hot metal in a general electric furnace. There is.
Prior art literature
Patent documents
[0008]
Patent Document 1: Japanese Patent Application Laid-Open No. 55-38975
Patent Document 2: Japanese Patent Application Laid-Open No. 1-247527
Patent Document 3: Japanese Unexamined Patent Publication No. 2009-46726
Patent Document 4: Japanese Unexamined Patent Publication No. 2013-72111
Patent Document 5: Japanese Unexamined Patent Publication No. 2004-76138
Patent Document 6: Japanese Patent Application Laid-Open No. 2003-1717113
Patent Document 7: Japanese Unexamined Patent Publication No. 2013-36056
Patent Document 8: Japanese Unexamined Patent Publication No. 2016-151036
Patent Document 9: Japanese Patent No. 5803824
Outline of the invention
Problems to be solved by the invention
[0009]
If an inexpensive carbon material containing a large amount of ash is used as a carbonizing material under conditions such as an electric furnace where the stirring strength is weak, the carbonizing rate may decrease as described above. It was invented that under conditions such as an electric furnace where the stirring intensity is weak, the carbonation rate becomes slow even at a lower ash concentration than that shown in Patent Document 1, and the influence of the ash concentration becomes remarkable at about 5% by mass or more. They found out. On the other hand, if the efficiency (that is, the carbonization rate) when using a carbon material having a high ash content can be increased more than the conventional knowledge, it is preferable because an inexpensive carbon material can be used with high efficiency. For that purpose, it is necessary to take measures to promote carbonation by removing the film formed on the carbonaceous surface due to the ash content in the carbon material. In addition, when the carbonized material is thrown in by free fall, unlike the powder supply by injection or bottom blowing, the contact area between the molten iron and the carbonized material is small, so the carbonization rate decreases and the slag before melting. There is a risk that the coal charging rate will decrease due to being taken in or scattered.
[0010]
The present disclosure has been made in view of such circumstances, and an object of the present invention is to provide a charcoal material which is inexpensive and has excellent reaction efficiency, and a charcoal method using the same.
Means to solve problems
[0011]
As a result of repeated studies to solve the above problems, the present inventors have found that the influence of the ash separation film on the carbonaceous surface can be reduced by adding quicklime to the carbon material. It was also found that the appropriate amount of quicklime varies depending on the content of SiO 2 and Al 2O 3 in the ash (sometimes referred to as "ASH" in the present disclosure).
[0012]
The gist of this disclosure is as follows.
<1> A charcoalizing material that charcoalizes molten iron stored in an electric furnace or ladle.
A carbonized material that is a mixture of quicklime and a carbon material having an ash content of 5% by mass or more and 18% by mass or less and that satisfies the following formulas (1) and (2).
0.6 ≦ (mc + Mc) / ms ≦ 2.7 ・ ・ ・ Equation (1)
0.7 ≦ (mc + Mc) / ma ≦ 6.5 ・ ・ ・ Equation (2)
Here, mc represents the mass of CaO in the carbon material, ms represents the mass of SiO 2 in the carbon material, ma represents the mass of Al 2O 3 in the carbon material, and Mc represents the mass of quicklime. Represents mass.
<2> The charcoal material according to <1>, wherein the mixture satisfies the conditions of the following formulas (1A) and (2A).
0.6 ≦ (mc + Mc) / ms ≦ 1.9 ・ ・ ・ Equation (1A)
0.7 ≦ (mc + Mc) / ma ≦ 5.0 ・ ・ ・ Equation (2A)
<3> A charcoal-charging method using the charcoal-forming material according to <1> above, in which gas is blown into the electric furnace or the ladle to stir the molten iron toward the molten iron surface formed. , A method of charcoalizing by adding the above-mentioned charcoalizing material.
<4> The charcoalizing method according to <3>, wherein the charcoal-adding material is added by pouring it from a lance toward the molten iron surface.
The invention's effect
[0013]
According to the present disclosure, it is possible to provide a carbonizing material which is inexpensive and has excellent reaction efficiency, and a carbonizing method using the same.
A brief description of the drawing
[0014]
[Fig. 1] Fig. 1 is a diagram for explaining a process of charging charcoal material from above using an arc-type electric furnace to charcoalize.
FIG. 2 is a diagram showing the relationship between the ratio C / S of CaO and SiO 2 in the carbonized material for each carbon material and the capacity coefficient.
FIG. 3 is a diagram showing the relationship between the ratio C / A of CaO and Al 2O 3 in the carbonized material for each carbon material and the capacity coefficient.
FIG. 4 is a diagram showing the magnitude of the carbon addition rate on the CaO-SiO 2-Al 2O 3 ternary phase diagram.
FIG. 5 is a diagram showing the relationship between the ratio C / S of CaO and SiO 2 in a carbonized material and the capacity coefficient at different stirring power densities.
FIG. 6 is a diagram showing the relationship between the ratio C / A of CaO and Al 2O 3 in a carbonized material and the capacity coefficient at different stirring power densities.
Embodiment for carrying out the invention
[0015]
Hereinafter, embodiments of the present disclosure will be described with reference to FIG.
As shown in FIG. 1, when charcoalizing molten iron, in an electric furnace 1 with a bottom blowing tuyere 4, a charcoalizing material is supplied from above the molten iron 5 using a lance 3 different from the electrode 2. , Stirring gas is flowed from the bottom blowing tuyere 4 to stir the molten iron.
[0016]
After putting the carbon material into the molten iron contained in the electric furnace or the pan, the temperature of the carbon material rises and the carbonaceous material melts from the surface of the carbon material, while the undissolved ash content ash content on the carbonaceous surface. It is thought to have the effect of forming a film and interfering with the contact between carbonaceous material and molten iron to reduce the carbonization rate. The main components of the ash (ASH) in the carbon material are SiO 2 and Al 2O 3, and when both are combined, most of the coal species account for 70% or more of the ash, and in many cases, about 90%.
The present inventors analyzed the ash separation film formed when such a carbon material was added upward to molten iron by electron microscopy and X-ray analysis. As a result, it was found that the composition of the ash separation film does not always match the composition of the ash content in the carbon material. In particular, it was found that most of SiO 2 in the ash content is reduced, and most of the ash separation film is a compound having a high melting point containing a large amount of Al 2O 3. Such compounds are mainly composed of components such as Al 2O 3, CaO · 6Al 2O 3, and spinel (MgO · Al 2O 3) having melting points of 1800 ° C. or higher. Further, when a charcoal-added material obtained by preliminarily adding quicklime powder to a carbon material and mixing it is used, CaO is added to the ash separation film and calcium silicate is formed to suppress the reduction of SiO 2. As a result, it was found that the composition of the ash separation film changed, approached the expected composition from the analysis value of the carbon material and the amount of quicklime added, and changed in the direction of lowering the liquidus temperature.
[0017]
In addition, although sulfur is often contained in naturally-derived carbon materials, it is known that sulfur in molten iron has the effect of inhibiting contact between carbon atoms and molten iron and reducing the carbonation rate. There is. On the other hand, as a result of experiments conducted by the present inventors, when a carbonized material in which quicklime is added to the carbon material is used, the rate of increase in the sulfur concentration in the molten iron during carburization is higher than that in the case where quicklime is not added. Clarified to decrease. Further, this desulfurization behavior was the same not only in a vacuum furnace or a closed furnace but also in a normal atmospheric furnace as long as there was no positive supply of an oxidizing gas such as oxygen gas or air. It is considered that this is because C and CaO in the carbon material are close to each other by adding quicklime powder and mixing in advance, and a reducing atmosphere is formed near the metal-slag interface.
[0018]
In this way, by using a charcoal material in which quicklime is mixed with a carbon material, the composition of the ash separation film formed on the surface of the molten iron or the carbon material is changed to prevent a decrease in the carbonization rate, and the surface of the molten iron It is expected to have the effect of increasing the reaction boundary area by local desulfurization.
[0019]
Next, various experiments were conducted to optimize the mixing amount of quicklime. Table 1 below shows the types of carbon materials used in this experiment.
[0020]
[table 1]

[0021]
The water content, ash content (ASH), volatile content, and fixed carbon content (% is mass%) in the carbon material shown in Table 1 are JIS. It is defined by M 8812: 2006, and specifically, it is measured by the following method.
Moisture: Weight loss when 5 g of a sample crushed to a particle size of 250 μm or less is dried at 107 ± 2 ° C to a constant weight.
Ash content (ASH): Residue when 1 g of sample is heated and ashed at 815 ± 10 ° C. Ratio (mass%) to 1 g of sample.
Volatile content: 1 g of a sample is placed in a platinum crucible with a lid, and water is removed from the weight loss when heating is performed by shutting off the air at 900 ± 20 ° C for 7 minutes.
Fixed carbon content: Fixed carbon content [mass%] = 100- (moisture [mass%] + ash [mass%] + volatile content [mass%]).
[0022]
Further, the composition of the ash content in the carbon material is defined by JIS M 8815: 1976, and specifically, it is measured by the following method. Further, SiO 2, Al 2O 3, and CaO represent mass% in the ash content.
SiO 2: The sample is melted with sodium carbonate, the melt is dissolved in hydrochloric acid, perchloric acid treatment is performed to dehydrate the silicic acid, and the mixture is filtered to store the precipitate. Silicic acid in the filtrate is recovered and combined with the main precipitate, and is strongly heat-ashed to obtain anhydrous silicic acid. Hydrofluoric acid and sulfuric acid are added to this to volatilize silicon dioxide, and the weight reduction is calculated.
Al 2O 3: Decompose the sample with hydrofluoric acid, nitric acid and sulfuric acid and melt it with potassium pyrosulfate. The melt is dissolved in hydrochloric acid, the pH is adjusted with acetic acid and aqueous ammonia, and heavy metals are extracted and removed with DDTC and chloroform. A certain amount of EDTA standard solution is added to this to form EDTA-aluminum complex salt, and excess EDTA is back titrated with zinc standard solution.
CaO: Collect the filtrate and washing liquid at the time of quantifying silicon dioxide, melt the residue after quantifying silicon dioxide with sodium pyrosulfate, combine the solution dissolved in hydrochloric acid, and hydroxide iron, aluminum, etc. with aqueous ammonia. Precipitate as and filter. Adjust the pH of the solution, precipitate magnesium hydroxide, mask the interfering components with potassium cyanide and titrate with EDTA standard solution using NN indicator.
[0023]
The present inventors use a small melting furnace of a scale of 2 kg to control the bottom blowing flow rate of bottom blowing gas stirring, add a carbonizing material while maintaining a predetermined molten iron temperature, and carbonize after adding the carbonizing material. A velocity measurement test was performed. First, quicklime powder was mixed with the six types of carbon materials shown in Table 1 to prepare a powdery carbonized material. After that, the electrolytic iron is melted in a small melting furnace, the carbonized material is dropped on the molten iron surface from above, the bottom-blown gas is agitated, and sampling is performed at appropriate time intervals to determine the time change of the carbon concentration in the molten iron. rice field. The addition ratio of quicklime powder was changed in the range of (mass of quicklime powder) / (mass of carbonized material) of 0.05 or more and 0.25 or less. The behavior of the coal addition rate is assumed to be a primary reaction driven by the difference between the saturated C concentration and the C concentration in molten iron, and the capacitance coefficient K in the following equation (3) is assumed to be a constant value. The coefficient K (1 / s) was calculated. Here, C S, C t, and C 0 are all C concentrations (mass%) in the molten iron, C S is the saturated C concentration, C t is the C concentration at time t (s), and C 0 is the time t. = Means a C concentration of 0.
Ln ((C S-C 0) / (C S-C t)) = K × t ・ ・ ・ Equation (3)
[0024]
The capacity coefficient K specified in the formula (3) is an index of the reaction efficiency of the carbonized material, and it can be judged that the larger the capacity coefficient K is, the faster the carbonized material is charged and the better the reaction efficiency is.
[0025]
The particle size of the carbonized material was adjusted to the range of 1.0 ± 0.4 mm by sieving. For bottom-blown gas stirring, an experiment was conducted in the range of ε = 0.02 to 0.30 at the stirring power density ε (kW / ton) calculated by the following formula (4). The range of this stirring power density was set as a range of practical values ​​for an electric furnace or a ladle.
Ε = 371 × Q × (T + 273) / V × {ln (1 + ρ × g × L / P) + 1- (T n + 273) / (T + 273)} ・ ・ ・ Equation (4)
In formula (4), Q: total flow rate of bottom-blown gas (Nm 3 / s), T: molten iron temperature (° C), V: molten iron volume (m 3), ρ: molten iron density (kg / m 3), g: Gravity acceleration (m / s 2), L: floating height of blown gas (m), P: atmospheric pressure (Pa), T n: blown gas temperature (° C.). In the test of the small melting furnace, L means the molten iron depth of the small melting furnace.
[0026]
In the test using this small melting furnace, the experiment was carried out while keeping the molten iron temperature T at 1400 ° C ± 20 ° C. As described above, the main composition of the ash separation film when no quicklime powder is added is a high melting point composition containing a large amount of Al 2O 3, which is a substantially upper limit of the temperature normally used in an electric furnace, which is 1700 ° C. or 1750 ° C. It has a composition that does not melt even at ° C. In the present disclosure, the composition of the ash separation film is controlled mainly by CaO-SiO 2-Al 2O 3 by mixing quicklime powder with the carbon material, but the liquidus temperature is 1350 ° C. or lower in these three components. Such a composition range is very narrow, and the ash composition in the carbon material varies from particle to particle, so it is difficult to stably control the amount of quicklime added so that the composition melts the ash film. Is.
[0027]
Therefore, a temperature near 1400 ° C was selected as a realistic temperature that can be stably applied, and evaluation was performed based on 1400 ° C. If the temperature is higher than this, the liquid phase has a wider composition and the viscosity also decreases. Therefore, if the amount of quicklime added is within the range evaluated at 1400 ° C, it is effective even at a molten iron temperature exceeding 1400 ° C. Under relatively high temperature conditions such as 1600 ° C, the same effect may be exhibited with a wider range of quicklime addition, but by making the composition effective at 1400 ° C, the fluidity becomes higher. It becomes high and a remarkable reaction promoting effect is expected. The molten iron temperature is practically preferably 1750 ° C. or lower, more preferably 1700 ° C. or lower, from the viewpoint of wear of refractories. In addition, there may be a local high temperature field such as an arc spot or a fire point due to a top-blown oxygen lance. As the molten iron temperature, the temperature of the reaction part should be used in principle, but since there is actually a problem in the measurable or uniform temperature distribution, the average molten iron temperature as a whole may be substituted.
[0028]
First, the experimental results at ε = 0.08 ± 0.01 kW / t are shown in FIGS. 2 and 3. Here, the ratio ({mc + Mc} / M) of the sum of the mass of CaO (mc) and the mass of fresh lime (Mc) in the ash contained in the carbon material to the mass (M) of the carbonized material is C, and the ash content. The ratio (ms / M) of the mass (ms) of SiO 2 in the mass (M) of the carbonized material is S, and the mass (ma) of Al 2O 3 in the ash is the mass (M) of the carbonized material. Assuming that the occupying ratio (ma / M) is A, C, S, and A represent the ratios of CaO, SiO 2, and Al 2O 3 contained in the carbonized material, respectively. The ratio of each component in the ash contained in the carbon material is the product of the ratio of ASH in the carbon material and the ratio of each component in ASH.
[0029]
In FIG. 2, the horizontal axis represents the ratio C / S (= (mc + Mc) / ms), and in FIG. 3, the horizontal axis represents the ratio C / A (= (mc + Mc) / ma). Further, the vertical axis represents a relative value of the capacity coefficient (K), and is a ratio with the capacity coefficient (K0) when a carbon material to which quicklime powder is not added, that is, K / K0.
[0030]
When the relative value K / K0 of the capacity coefficient exceeds 1.2, it can be judged that the coal charging rate is significantly improved even if the experimental variation is subtracted. As shown in FIG. 2, when the ratio C / S is 0.6 or more and 2.7 or less, the relative value K / K0 of the capacity coefficient often exceeds 1.2. Further, as shown in FIG. 3, when the ratio C / A is 0.7 or more and 6.5 or less, the relative value K / K0 of the capacity coefficient often exceeds 1.2. Further, when the ratio C / S is 0.6 or more and 1.9 or less and the ratio C / A is 0.7 or more and 5.0 or less, the relative value K / K0 of the capacity coefficient exceeds 1.5, which is remarkable. It was confirmed that the coal addition rate was improved. However, as shown in FIGS. 2 and 3, when considering only one of the ratio C / A and the ratio C / S, the relative value K / K0 of the capacitance coefficient is 1.2 or less, or 1 even within the above region. There was also a condition where the value was 5.5 or less. On the other hand, in the case where the ratio C / S is 0.6 or more and 2.7 or less and the ratio C / A is 0.7 or more and 6.5 or less, the relative value K / K0 of the capacity coefficient exceeds 1.2. Was there.
[0031]
FIG. 4 is a diagram showing the relationship between the phase diagram of the SiO 2-CaO-Al 2O 3 ternary system and the experimental results. In FIG. 4, when the relative value K / K0 of the capacity coefficient exceeds 1.5, it is “a group”, and when the relative value K / K0 of the capacity coefficient is more than 1.2 and 1.5 or less, it is “b group”. , When the relative value of the capacity coefficient is K / K0 = 1.2 or less, it is regarded as "c group". The carbon material to which quicklime powder was not added shown in Table 1 was designated as "d group".
[0032]
In FIG. 4, the liquid phase line at 1400 ° C. and the line showing C / S = 0.6, 1.9, 2.7, C / A = 0.7, 5.0, 6.5 are also shown. rice field. As a result, the "b group" exists only in the region surrounded by C / S = 0.6, C / S = 2.7, C / A = 0.7, and C / A = 6.5, and " The "a group" existed only in the region surrounded by C / S = 0.6, C / S = 1.9, C / A = 0.7, and C / A = 5.0. When either the ratio C / S or the ratio C / A deviated from the above region, the relative value K / K0 of the capacitance coefficient did not exceed 1.2.
[0033]
The region of the ratio C / A of "group b" and "group a" was almost the same as the region where the composition of the liquid phase was present at 1400 ° C. On the other hand, the region of the ratio C / S that becomes the "b group" and the "a group" partially overlaps with the region of the composition that becomes the liquid phase at 1400 ° C., but the region is shifted as a whole. .. In the region where the ratio C / S is smaller than 0.6, the viscosity is high even in the composition of the liquid phase at 1400 ° C., and it is presumed that the removal of the ash separation film by stirring did not work effectively. On the other hand, in the region where the ratio C / S is 1.3 or more and 2.7 or less, although it is not a liquid phase composition, CaO is saturated and desulfurization near the interface occurs in the reduction field formed by the carbon material. However, it is presumed that the carbonation rate improved as a result.
[0034]
Actually, it has been shown that the increase in the S concentration in molten iron tends to be suppressed as the ratio C / S is larger. Further, it can be estimated that the excessive presence of CaO secures a sufficient opportunity for contact between the exposed ash and CaO due to the dissolution of the carbon in the carbon material, and the effect that the composition of the ash film is likely to change is likely to occur. .. However, in the region where the ratio C / S is more than 1.9 and 2.7 or less, there are many solid and unreacted quicklime, and this unreacted quicklime inhibits the contact between the molten iron and the carbon material, so the carbon addition rate is high. It is considered that the ratio C / S was lower than that in the region of 1.9 or less. Further, when the ratio C / S is more than 2.7, the contact inhibition effect by the quicklime powder becomes strong, and the carbonization rate is not improved as compared with the case where the quicklime powder is not added. Has decreased.
[0035]
From the above experiments, it is important that the carbonized material of the present disclosure satisfies the conditions of 0.6 ≦ C / S ≦ 2.7 and 0.7 ≦ C / A ≦ 6.5, and it is added in this range. The charcoal rate is significantly improved, and the effect of improving the charcoal rate is particularly large in the range where the conditions of 0.6 ≦ C / S ≦ 1.9 and 0.7 ≦ C / A ≦ 5.0 are satisfied. I understand.
[0036]
Next, the results of changing the stirring power density of coal A in the same small furnace are shown in FIGS. 5 and 6. As shown in FIGS. 5 and 6, the same C / S region and the same C / as in the case of ε = 0.08 kW / t at all stirring intensities of ε = 0.02, 0.18, 0.30 kW / t. In the A region, an increase in the coal addition rate was confirmed. From the above results, when 0.6 ≦ C / S ≦ 2.7 and 0.7 ≦ C / A ≦ 6.5 are satisfied, it is preferable that 0.6 ≦ C / S ≦ 1.9 and 0. When the condition of .7 ≦ C / A ≦ 5.0 was satisfied, the effect of improving the coal addition rate was obtained regardless of the strength of the stirring intensity.
[0037]
The ratio R of quicklime contained in the carbonized material when the above conditions of ratio C / S and ratio C / A are satisfied can be calculated by the following procedure. The sum of the mass of SiO 2 in the ash (ms) and the mass of Al 2O 3 in the ash (ma) is added. It does not exceed the amount of ash in the carbon material contained in the carbon material. Therefore, if the ratio of quicklime in the carbonized material is R (= Mc / M) and the ratio of ash in the carbon material is (ASH), the following formula (5) is established.
Ms + ma ≤ M x (1-R) ​​x (ASH) ... Equation (5)
Further, by multiplying both sides of the equation (5) by C / (ms + ma) and using the relationship of R≤C, the following equation (6) is obtained.
R≤C≤ (1-R) ​​x (ASH) / {1 / (C / S) + 1 / (C / A)} ... Equation (6)
[0038]
Here, the variable X is defined by the following equation (7).
X = (ASH) / {1 / (C / S) + 1 / (C / A)} ... Equation (7)
In this case, X is a monotonous increase with respect to (ASH), ratio C / S, and ratio C / A, respectively.
By transforming equation (6) and substituting equation (7), the following equation (8) is obtained.
R ≦ 1 / (1 + 1 / X) ・ ・ ・ Equation (8)
[0039]
Here, since the right side of the equation (8) increases monotonically with respect to X, the larger the ash ratio (ASH), the ratio C / S, and the ratio C / A, the larger the upper limit of the quicklime ratio R. Substituting in the preferable ranges of the ratio C / S and the ratio C / A described above, the ratio R of quicklime in the carbonized material is about 19.9% ​​at the maximum.
[0040]
As described above, the content of quicklime can be suppressed compared to the conventional method. Although there is an increase in cost due to the use of a mixing device for carbon material and quicklime, in addition to the cost reduction due to the high carbonation rate, there is also a cost reduction effect due to the reduction of clogging in the pipe due to the moisture absorption effect of quicklime. Occurs. As a result, the operating cost is greatly reduced as a whole, the use of low-grade carbon material can be promoted, and the cost of carbonized material can be significantly reduced.
[0041]
Although the mixed powder was used as a carbonizing material in this experiment, it may be a carbonizing material obtained through a mass forming process such as briquetting. In the case of briquette, the carbon material and quicklime, which is an additive, are closer to each other, so that the removal effect by modifying the ash separation film becomes larger.
[0042]
In addition, if the carbonized material can be charged by free fall from above the furnace, equipment related to gas transfer can be omitted, and restrictions on the particle size of the carbonized material can be relaxed, reducing costs. Taking this into consideration, the maximum particle size of the carbon material as the carbonizing material is preferably 20 mm or less in order to secure the contact area with the molten iron and secure the carbonizing rate. However, when coal containing 10% or more of volatile matter is used as the carbon material, the volatile matter is volatilized by heating until contact with molten iron and becomes shattered, so the maximum particle size is not limited to 20 mm or less. It can be used up to a maximum particle size of 100 mm or less. In addition, when the carbon material is added from above, if the particle size is too small, it will not reach the molten iron and will be discharged to the outside of the furnace together with the exhaust gas, resulting in loss. Therefore, the lower limit of the maximum particle size of the carbon material is 0.2 mm. It is preferable to do so.
[0043]
Further, when the amount of ash in the carbon material is large, even if the ash film is modified by mixing quicklime, the amount of ash film may become too large and may not be effectively removed from the interface. Therefore, the upper limit of the ash content in the carbon material is 18% by mass. Further, the smaller the ash content in the carbon material, the less effective the mixing of quicklime is, and the carbon material having a lower ash content is expensive. In consideration of cost, the lower limit of the ash content in the carbon material is 5% by mass.
[0044]
The additive to be mixed with the carbon material is quicklime whose main component is CaO. Even if CaCO 3-based material such as limestone is used as an additive, CO 2 is desorbed to form CaO when it is added to the furnace and heated, so in principle the same effect as quicklime is expected. However, in reality, the effect is not as expected. The reason is that the CO 2 desorption reaction is an endothermic reaction, and the carburizing reaction is also an endothermic reaction. It is thought that this is the reason.
The CaO content in quicklime mixed with the carbon material is preferably 80% by mass or more, more preferably 90% by mass or more.
[0045]
The particle size of quicklime to be added is preferably 10 mm or less in order to uniformly disperse it on the surface of the carbon material and exert its effect. Further, more preferably, quicklime is in the form of powder, and the maximum particle size is 1 mm or less.
[0046]
Next, the carbonation method using the carbonization material as described above will be described. In the example shown in FIG. 1, an AC electric furnace is used, but if the point of supplying the charcoal material from above the molten iron surface and the point of being able to stir with gas are common, the AC electric furnace shown in FIG. 1 is used. Not limited to. In the present embodiment, an AC electric furnace, a DC electric furnace, or a ladle is assumed as a refining container for carbonizing under a condition where the stirring strength is weak. It is not assumed that coal will be added under strong stirring conditions using a converter type refining facility.
[0047]
In principle, quicklime is mixed with the charcoal material to reform the ash separation film, and when the molten slag comes into contact with the charcoal material, the effect of mixing quicklime is reduced. Therefore, when the molten slag layer is present on the molten iron, the bottom blowing gas is blown from the bottom blowing tuyere to stir the molten iron to locally expose the molten iron surface, and the charcoal material is applied to the molten iron surface. It is preferable to put it in direct contact. Regardless of the type of bottom-blown gas, injection may be used instead of bottom-blown as a stirring method using gas. A solid component may be present in the molten slag layer.
[0048]
Further, in the example shown in FIG. 1, the charcoal material is supplied from the lance 3 together with the transport gas, but the charcoal material may be supplied from a plurality of lances, or the charcoal material may be supplied by free fall. .. Further, there may be a cold iron source that remains undissolved when the carbonized material is added. Further, the S concentration of the molten iron to be carbonized is preferably 0.5% by mass or less from the viewpoint of operability at the time of de-S.
Example
[0049]
Next, an example performed to confirm the action and effect of the carbonized material of the present disclosure will be described. The data shown in this example is merely an example of a case in which the present disclosure is applied, and the scope of application of the present disclosure is not limited thereto.
[0050]
Using an actual arc-type bottom-blown electric furnace (electric furnace 1) capable of melting 90 tons of molten iron as shown in FIG. 1, iron scrap was melted by arc heating from a graphite electrode (electrode 2). Further, N 2 gas was blown from the bottom blowing tuyere 4 and the molten iron was stirred to measure the temperature of the molten iron. The number of bottom blowing tuyere was 6, and the gas flow rate from each tuyere was adjusted to be uniform. After that, the carbonized material is thrown upward from the lance 3 by free fall, the temperature is measured and sampled at regular intervals while controlling the stirring intensity, the molten iron temperature and C concentration are measured, and the capacity is calculated from the above formula (3). The coefficient K was calculated. The lance 3 was installed directly above one of the bottom-blown tuyere 4, and the surface of the molten iron was exposed by stirring with the bottom-blown gas, and a carbonizing material was added to the exposed portion. The stirring power density at this time was ε = 0.18 kW / t. In addition, arc energization was carried out under some conditions during carbonization. The carbonized material is a mixture of a carbon material having a maximum particle size of 20 mm and quicklime powder having a maximum particle size of 1 mm (CaO content in quicklime: 90% by mass), and the carbon material is coal A shown in Table 1. , Coal C was used. In addition, in the reference example, a carbonized material containing only a carbon material not mixed with quicklime powder was used. Table 2 shows the main operating conditions.
Regarding the "judgment" in Table 2, when the capacity coefficient K0 of the reference example to be compared is 1.0 in comparison with the reference example under the same conditions (same coal type, same temperature) except that quicklime powder is mixed. If the relative value K / K0 of is more than 1.0, it is considered that the coal charging rate is improved by mixing the quicklime powder. When the relative value K / K0 of the capacity coefficient exceeds 1.2, it is judged that the coal charging rate has improved significantly and it is judged as Y (pass), and when it is 1.2 or less, it is judged that no significant improvement is seen. And N (failure). Specifically, Example 3 was compared with Reference Example 9, Example 4 was compared with Reference Example 8, and the others were compared with Reference Example 7.
[0051]
[Table 2]

[0052]
All of Examples 1 to 4 shown in Table 2 are conditions in which the ratio C / S and the ratio C / A satisfy the ranges of 0.6 to 2.7 and 0.7 to 6.5, respectively. In this case, the relative values ​​of the capacitance coefficients were all Y, which was a good result. Comparing Example 4 and Reference Example 8, even when coal C having a large amount of ASH is used, the amount of ASH and volatile matter is smaller than that of coal C by using a carbonizing material mixed with quicklime powder in an appropriate ratio. It was shown that a significant increase in coal loading rate over coal A could be achieved. In Example 3, the molten iron temperature was 1600 ° C., but a significant increase in the carbonation rate was confirmed by mixing quicklime powder with the carbonizing material in the same manner as in the 1500 ° C. condition.
[0053]
In Comparative Example 5, the ratio C / A was in the range of 0.6 to 2.7, but the ratio C / S was out of the range of 0.7 to 6.5. In this case, the relative value of the capacity coefficient was 1.17 even when compared with Reference Example 7, and no significant increase in the coal charging rate was observed.
[0054]
On the other hand, in Comparative Example 6, both the ratio C / S and the ratio C / A were out of the above range (C / S: 0.6 to 2.7, C / A: 0.7 to 6.5). .. In this case, the relative value of the capacity coefficient was 0.42 as compared with Reference Example 7, and the coal charging rate decreased.
[0055]
As described above, in the examples of the present disclosure, it was confirmed that it is possible to accelerate the carbonization rate even by using a carbon material having a high ASH that is poorly soluble.
[0056]
Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the configuration described in the above-described embodiments, and the matters described in the claims. It also includes other embodiments and variations that may be considered within the scope.
Code description
[0057]
1 Electric furnace
2 Electrode
3 lance
4 Bottom blowing tuyere
5 molten iron
[0058]
The entire disclosure of Japanese patent application 2018-230108 filed on December 7, 2018 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are referenced herein to the same extent as if individual documents, patent applications, and technical standards were specifically and individually described. Is taken in by.
The scope of the claims
[Claim 1]
It is a charcoalizing material that charcoalizes molten iron stored in an electric furnace or ladle.
A carbonized material that is a mixture of quicklime and a carbon material having an ash content of 5% by mass or more and 18% by mass or less and that satisfies the following formulas (1) and (2).
0.6 ≦ (mc + Mc) / ms ≦ 2.7 ・ ・ ・ Equation (1)
0.7 ≦ (mc + Mc) / ma ≦ 6.5 ・ ・ ・ Equation (2)
Here, mc represents the mass of CaO in the carbon material, ms represents the mass of SiO 2 in the carbon material, ma represents the mass of Al 2O 3 in the carbon material, and Mc represents the mass of quicklime. Represents mass.
[Claim 2]
The carbonized material according to claim 1, wherein the mixture satisfies the following formulas (1A) and (2A).
0.6 ≦ (mc + Mc) / ms ≦ 1.9 ・ ・ ・ Equation (1A)
0.7 ≦ (mc + Mc) / ma ≦ 5.0 ・ ・ ・ Equation (2A)
[Claim 3]
It is a charcoalizing method using the charcoalizing material according to claim 1 or 2.
A charcoalizing method in which gas is blown into the electric furnace or the ladle to stir the molten iron toward the molten iron surface, and the carbonizing material is added to carbonize the molten iron.
[Claim 4]
The carbonation method according to claim 3, wherein the carbonizing material is added by pouring it from a lance toward the molten iron surface.