Method for producing molten iron

Abstract

To provide a method for producing molten iron capable of suppressing unintended ejection of exhaust gas to the outside of the furnace when a biomass-derived carbon material is charged.SOLUTION: A method for producing molten iron, in which an iron-containing coolant is charged into a furnace together with molten pig iron, followed by oxygen blowing refining, comprises: charging a biomass-derived carbon material into the furnace during a period from before the start to the end of the oxygen blowing refining; and melting the iron-containing coolant by heat generated from the oxygen blowing refining of the molten pig iron, by combustion heat of the biomass-derived carbon material due to oxygen supplied in the oxygen blowing refining, and by sensible heat of the molten pig iron. The amount of the carbon material charged is set based on an exhaustible amount of exhaust gas generated from the carbon material, a molar amount of volatile gas generated from the carbon material, and a molar ratio of exhaust gas to volatile gas when the volatile gas is completely combusted.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing molten iron. [Background technology]

[0002] In recent years, reducing CO2 emissions has become an important issue for the purpose of protecting the global environment and preventing global warming. In particular, reducing CO2 emissions is a top priority for steelworks, as it affects the very survival of the company. Meanwhile, from the perspective of resource conservation and environmental issues, recycling the large amount of iron scrap generated in steelworks to manufacture steel products has become a technological challenge. This is because, while the production of molten iron in a blast furnace requires a great deal of energy to reduce and melt iron ore, iron scrap only requires heat for fusion. Therefore, using iron scrap reduces the amount of energy used for the heat required to reduce iron ore, thereby achieving energy savings and CO2 reduction.

[0003] Conventionally, electric arc furnaces have been commonly used as refining equipment for producing molten iron from iron scrap. However, conventional electric arc furnaces consume a large amount of electricity to melt iron scrap, which increases production costs in countries with high electricity prices, such as Japan. Therefore, as a method for economically melting iron scrap without using an electric arc furnace, a method has been proposed in which a converter-type refining furnace with a high oxygen gas supply capacity is used to burn inexpensive carbonaceous material with oxygen gas, and the combustion heat of the carbonaceous material is used as a heat source to melt the iron scrap and produce molten iron.

[0004] For example, Patent Document 1 describes a method for producing high-carbon molten iron with a carbon concentration of 3.0 mass % or more in a refining furnace by charging iron scrap and molten pig iron as iron sources into the refining furnace, then supplying oxygen gas into the refining furnace, melting the iron scrap in the refining furnace by the combustion heat of the oxygen gas from the carbonaceous material supplied into the refining furnace and the sensible heat of the molten pig iron, and recarburizing the molten iron produced by the melting of the iron scrap with the carbon in the carbonaceous material and the carbon in the molten pig iron, in which biomass-derived carbonaceous material is used as the entire carbonaceous material, and the total amount of biomass-derived carbonaceous material added is X The present invention describes a method for producing high-carbon molten iron using iron scrap, characterized in that the total amount of carbonaceous material added, X, is equal to or less than the value calculated by the following formula (1), where X is (kg-carbonaceous material / t-molten iron), a is the sulfur concentration of the carbonaceous material (mass %), b is the weighted average of the sulfur concentrations of the molten pig iron and iron scrap before refining, and c is the maximum allowable sulfur concentration of the high-carbon molten iron at the end of refining (mass %), and the amount of iron scrap to be charged is determined based on this total amount of carbonaceous material added, X, and the sulfur concentration of the high-carbon molten iron to be produced is controlled to be equal to or less than the maximum allowable sulfur concentration c. X = [(cb) / a] × 1000 (1)

[0005] Furthermore, Patent Document 2 describes a converter heating material made by molding a binder and a carbonized material obtained by carbonizing plant biomass, and the composition in a dry state is 70 mass% or more of fixed carbon, 20 mass% or less of volatile components, 0.1 mass% or less of sulfur, and the remainder is ash, and the carbonized material has a particle size of 3 mm or less.

[0006] Patent Document 3 also describes a converter exhaust gas recovery facility equipped with an induced draft fan for sucking exhaust gas generated from a converter, which includes a blowing pattern calculation means for determining a blowing pattern representing the oxygen supply rate, lance height, bottom blown gas flow rate, bottom blown gas type, and instruction amounts and change timings for the auxiliary material input for the refining process based on operation information including the type of treatment, molten pig iron information, scrap charging information, molten steel target composition, auxiliary material input information, treatment time, and converter equipment status, and an exhaust gas flow rate calculation means for estimating the exhaust gas flow rate from the converter based on the blowing pattern determined by the blowing pattern calculation means. and dust collection capacity calculation means for calculating the amount of dust contained in the exhaust gas from the pressure generated by the induced draft fan at the rotation speed of the induced draft fan determined by the rotation speed calculation means, comparing the amount of dust contained in the exhaust gas with a predetermined environmental standard value, and setting the determined rotation speed as the rotation speed of the induced draft fan if the dust content is smaller than the environmental standard value, and recalculating the rotation speed to satisfy the environmental standard value if the dust content is larger than the environmental standard value.

[0007] Patent Document 4 describes a steel refining method using a converter-type vessel, which comprises charging an iron-containing chill material together with molten pig iron into a converter-type vessel, carrying out a preparatory treatment for desiliconization, then carrying out an intermediate slag removal treatment in which at least a portion of the slag generated during the preparatory treatment for desiliconization is discharged, and after this treatment, charging a carbonaceous material into the converter-type vessel and carrying out a treatment to promote the dissolution of the iron-containing chill material by supplying a heat source by blowing oxygen into the converter-type vessel. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5942425 [Patent Document 2] Patent No. 5846289 [Patent Document 3] Patent No. 3804526 [Patent Document 4] Patent No. 6744586 Summary of the Invention [Problem to be solved by the invention]

[0009] In the above Patent Documents 1 and 2, when high-carbon molten iron is produced using iron scrap, carbon-neutral carbonaceous material derived from biomass is effectively utilized as a heat source and recarburizer in place of carbonaceous material derived from fossil fuels such as coke and coal, thereby using iron scrap that can reduce the amount of greenhouse gas emissions.

[0010] Furthermore, Patent Document 3 discloses that unburned gas can be recovered over a wide range of oxygen flow rates in a converter, such as during the decarburization and dephosphorization processes of hot metal. Furthermore, Patent Document 4 discloses that in steelmaking refining in which scrap and other materials are melted together with hot metal in a converter, a large amount of carbon material is used to ensure the carbon content in the molten metal and the carburization time in order to promote the melting of the scrap and other materials.

[0011] However, depending on the timing of charging biomass-derived carbonaceous material, if a large amount is charged at once, the volatile components contained in the carbonaceous material may volatilize, increasing the volume of exhaust gas and exceeding the amount that can be discharged through the equipment's exhaust gas system. In this case, the exhaust gas that cannot be completely discharged is ejected outside the furnace together with dust and volatile gases, causing problems such as the generation of dust and the ejection of flames. However, Patent Documents 1 to 4 do not take this effect into consideration.

[0012] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a method for producing molten iron that can suppress unintended emission of exhaust gas outside the furnace when charging carbonaceous material derived from biomass. [Means for solving the problem]

[0013] In order to solve the above problems, according to one aspect of the present invention, there is provided a method for producing molten iron by charging an iron-containing chill material into a furnace together with molten pig iron and then performing oxygen-blown smelting, the method including charging a biomass-derived carbonaceous material into the furnace between before the start and end of the oxygen-blown smelting, and melting the iron-containing chill material using the heat generated by the oxygen-blown smelting of the molten pig iron, the heat of combustion of the biomass-derived carbonaceous material by the oxygen in the oxygen-blown smelting, and the sensible heat of the molten pig iron, wherein the amount of carbonaceous material charged is set based on the amount that can be discharged relative to the exhaust gas generated from the carbonaceous material, the molar amount of volatile gases generated from the carbonaceous material, and the molar ratio of the exhaust gas to the volatile gases when the volatile gases are completely combusted.

[0014] The biomass-derived carbonaceous material may be charged into the furnace in multiple batches.

[0015] The amount of the biomass-derived carbonaceous material charged each time may be set so as to satisfy the following relational expression (A).

[0016]

number

[0017] Where, V is the amount of exhaust gas that can be emitted from the carbonaceous material, M coal : Amount of carbon material charged at one time (g), m gas where V is the molecular weight of the volatile gas generated from the carbonaceous material, C is the molar ratio of the exhaust gas to the volatile gas when the volatile gas is completely burned, and D is the volatile content in the carbonaceous material. Note that V = r V ext r: Exhaust gas increase coefficient due to charging of carbonaceous material, V ext : The amount of exhaust gas that can be emitted per unit time in the refining facility (Nm 3 / h).

[0018] Biomass-derived carbonaceous material contains a carbonized material obtained by carbonizing plant biomass and a binder, and the composition of the carbonaceous material in a dry state is 70% by mass or more of fixed carbon, 25% by mass or less of volatile components, 0.1% by mass or less of sulfur, and the remainder is ash. [Effects of the Invention]

[0019] As described above, the present invention provides a method for producing molten iron that can suppress unintended emission of exhaust gas outside the furnace when charging carbonaceous material derived from biomass. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram illustrating an example of a schematic configuration of a refining facility according to an embodiment. [Figure 2] FIG. 1 is a diagram showing an example of an Fe—C binary equilibrium phase diagram. [Figure 3] FIG. 4 is a diagram showing an example of a change in carbon concentration in molten steel during oxygen supply. [Figure 4] FIG. 2 is a diagram showing an example of the relationship between the amount of carbonaceous material charged and the amount of exhaust gas generated. [Figure 5] FIG. 2 is a schematic diagram showing an example of the relationship between the timing of charging carbonaceous materials and the amount of exhaust gas. [Figure 6] FIG. 2 is a diagram showing an example of the relationship between the amount of carbonaceous material charged and the change in furnace pressure. [Figure 7] 1 is a flowchart showing an example of the flow of a carbonaceous material charging process. [Figure 8] FIG. 2 is a schematic diagram showing an example of the relationship between the timing of charging carbonaceous materials and the amount of exhaust gas. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0022] First, an embodiment in which the present invention is applied to a top and bottom blown converter refining furnace facility will be described as an example. Fig. 1 is a schematic diagram of a vertical cross section of a top and bottom blown converter refining furnace facility to which the present invention is applied.

[0023] The converter-type refining furnace facility 1 (i.e., the refining facility 1) is composed of a converter-type vessel 2 (i.e., the converter 2) into which iron scrap 14 and molten pig iron 12 are charged and which produces molten iron from the charged iron scrap 14 and molten pig iron 12, a top-blowing oxygen lance 4 which can move up and down into the internal space of the converter 2 through a throat 3 at the top of the converter 2, a gas recovery device (not shown) which recovers exhaust gas (mainly CO gas) generated from the converter 2 through a duct 8 covering the throat 3, and a raw material charging device which includes hoppers 9A and 9B, discharge devices 10A and 10B, and a chute 11 as a part of the raw material charging device. The converter 2 is equipped with a bottom-blowing tuyeres 5 which penetrate the bottom of the furnace and a tapping port 7 which penetrates the side wall. The bottom-blowing tuyere 5 is connected to a gas inlet pipe 6, and a stirring gas such as Ar gas or nitrogen gas or refining oxygen gas is supplied via the gas inlet pipe 6 and blown from the bottom-blowing tuyere 5 as a bottom-blowing gas. A chute 11 passes through the duct 8 and reaches directly above the furnace opening 3, and auxiliary materials are charged into the furnace from the furnace opening 3 via the chute 11.

[0024] Using the top and bottom blown converter refining furnace facility 1 configured as above, the present invention is carried out as follows.

[0025] First, scrap iron 14 and molten pig iron 12 are charged into the converter 2 as main raw materials. In the present invention, the scrap iron 14 is basically melted by the heat of reaction between the carbonaceous material 15 supplied to the converter 2 and the oxygen gas supplied to the converter 2 from the top-blowing lance 4, i.e., the heat of combustion of the carbonaceous material 15. Therefore, the blending ratio of the scrap iron 14 (combining ratio of scrap iron = charged amount of scrap iron × 100 / (charged amount of molten pig iron + charged amount of scrap iron)) does not need to be specified in particular when sulfur contamination from the carbonaceous material 15 is not taken into consideration, and can be set according to the amount of carbonaceous material 15 used. In other words, the amount of carbonaceous material 15 used can be set according to the blending ratio of the scrap iron 14. However, if the blending ratio of the scrap iron 14 is too high, the melting time will be long. Therefore, the blending ratio of the scrap iron 14 should be set to a maximum of about 50 mass%. The molten iron 12 to be used is subjected to pre-treatment (desulfurization and desiliconization) as necessary. After dephosphorization in the converter 2, intermediate slag removal is performed, and further decarburization is performed.

[0026] Iron scrap 14 is charged into the furnace according to a blending ratio set based on the amount of carbonaceous material 15 used as a heat source, and then molten iron 12 is charged into the furnace according to the blending ratio. Thereafter, a predetermined amount of biomass-derived carbonaceous material 15 stored in a hopper 9A is cut out by a cutting device 10A and charged into the furnace as a heat source from the furnace throat 3 via a chute 11. In this case, a portion of the carbonaceous material 15 may be charged into the furnace in advance together with the iron scrap 14.

[0027] The carbonaceous material 15 includes biomass-derived carbonaceous material. The biomass-derived carbonaceous material included in the carbonaceous material 15 is formed, for example, by molding a binder and a carbonized product of carbonizing plant biomass. The plant biomass used as a raw material is, for example, woody, herbaceous, or agricultural residue-based plant biomass. The biomass-derived carbonaceous material has a dry composition of 70% by mass or more of fixed carbon, 25% by mass or less of volatile components, 0.1% by mass or less of sulfur, and the remainder being ash. The carbonaceous material 15 may also include carbonaceous material derived from waste plastic raw materials.

[0028] Furthermore, in order to form molten slag 13 for refining in the furnace, slag-forming materials such as quicklime, fluorite, and dolomite are charged into the converter 2 via a raw material charging device (not shown). Furthermore, if there is a thermal margin in a heat calculation that compares the calorific value calculated from the amount of carbonaceous material 15 added with the amount of slag-forming material added and the target temperature value of the molten iron at the time of tapping, an iron source 16 in an amount corresponding to this thermal margin is discharged from the hopper 9B by the discharge device 10B and charged into the furnace via the chute 11. The iron source 16 supplied from the hopper 9B functions as a coolant.

[0029] The iron source 16 is selected from one or more of iron ore, sintered iron ore, mill scale, steelmaking dust, magnetically separated scrap, and steel cuttings generated in machine shops. Even if the iron source 16 contains FeO or Fe2O3, these are reduced to iron by the carbon contained in the molten iron 12 and the carbonaceous material 15 in the furnace, thereby making effective use of resources. Magnetically separated scrap is the metal content that is mixed in converter slag and recovered from crushed slag by magnetic separation.

[0030] After that, refining begins by supplying oxygen gas from the top-blown oxygen lance 4 into the furnace while injecting bottom-blown gas from the bottom-blown tuyeres 5. Part of the carbonaceous material 15 dissolves in the molten pig iron 12, increasing the carbon concentration of the molten pig iron 12. In other words, the carbonaceous material 15 functions to carburize the molten iron produced by the melting of the iron scrap 14 and the molten pig iron 12. In this case, the carbon in the carbonaceous material 15 is combusted by the oxygen gas according to the reaction formula "2C + O2 = 2CO." The combustion heat is transferred to the molten pig iron 12 via the molten slag 13, melting the iron scrap 14 embedded in the molten pig iron 12. However, because heat generated by the decarburization reaction of the molten pig iron 12 also contributes to the melting of the iron scrap 14, it is not necessary to completely prevent the decarburization reaction of the molten pig iron 12. By suppressing the decarburization reaction of the molten iron 12 as much as possible and at the same time, the carbon material 15 functions as a recarburizer, the carbon concentration of the produced molten iron may be set to 3.0 mass% or more. During this refining, the carbon material 15 and an iron source 16 in an amount corresponding to the amount of the carbon material 15 added are appropriately charged into the furnace from the throat 3 via the chute 11.

[0031] Furthermore, if the oxygen gas supplied from the top-blown oxygen lance 4 directly impinges on the molten pig iron 12, a decarburization reaction (2C + O2 = 2CO) of the molten pig iron 12 occurs, reducing the carbon concentration of the molten iron produced. Therefore, the flow rate and pressure of the oxygen gas supplied from the top-blown oxygen lance 4 are set so that as little of the oxygen gas as possible is consumed in the decarburization reaction of the molten pig iron 12 as possible and is mainly consumed in the combustion of the carbonaceous material 15.

[0032] After a predetermined amount of carbonaceous material 15 and oxygen gas are supplied and the iron scrap 14 is melted to produce molten iron at a predetermined temperature with a carbon concentration of 3.0 mass % or more, an Fe-Mn alloy, a Si-Mn alloy, or the like is added to the molten iron from a raw material charging device (not shown) as needed, and then the converter 2 is tilted by a tilting device (not shown) and the molten iron is discharged from the tap hole 7 into a ladle (not shown), thereby completing the production of molten iron using the iron scrap 14.

[0033] However, when charging carbonaceous material 15 at a time, if a large amount of carbonaceous material 15 is charged, the carbonaceous material 15 does not completely melt in the furnace, resulting in the discharge of the carbonaceous material 15. Specifically, as shown in the Fe-C binary equilibrium phase diagram in Figure 2, the saturated carbon concentration (i.e., the carbon concentration that can dissolve in liquid Fe) is approximately 5% at temperatures between 1400 and 1500 °C, at the liquidus line in the liquid phase region / liquid phase + graphite two-phase coexistence region. Therefore, in the range above the saturated carbon concentration of approximately 5% (to the right of the liquidus line in Figure 2), carbon does not completely dissolve in liquid Fe and precipitates as graphite. In other words, even if a large amount of carbonaceous material 15 is charged, the carbon does not completely dissolve, and the carbonaceous material 15 remains in the slag discharge, preventing its effective use as a heat source. Furthermore, depending on the amount of iron scrap 14 added, the temperature of the molten iron may decrease, further reducing the saturated carbon content.

[0034] Therefore, after extensive research, the inventors have come up with the idea of ​​charging the carbonaceous material 15 in multiple batches, rather than charging a large amount of the carbonaceous material 15 at once, so that the carbon concentration in the molten iron immediately after charging is equal to or less than the saturated carbon concentration.

[0035] The change in the carbon concentration in the molten pig iron due to one charging of the carbonaceous material 15 can be estimated using a stoichiometric model based on the decarburization reaction (2C + O2 = 2CO) of the molten pig iron 12 by oxygen gas supplied from the top-blown oxygen lance 4, and a reaction kinetic model in which carbon in the carbonaceous material 15 diffuses into the molten pig iron. The amount of the carbonaceous material 15 charged in one charging is set based on the above-mentioned model so that the carbon concentration in the molten pig iron after charging is equal to or lower than the saturated carbon concentration. The number of chargings is set based on the set amount of the carbonaceous material 15 charged in one charging and the total amount of the carbonaceous material 15 that needs to be charged as a heat source.

[0036] The amount of carbonaceous material 15 charged at one time may be set to an amount that allows complete combustion of the carbonaceous material 15 based on the molar amount of the carbonaceous material 15 and the amount of oxygen fed. Specifically, the carbon molar amount n coal The molar amount of oxygen supplied since the previous carbonaceous material 15 was charged is n O2 In this case, the charging amount of the carbonaceous material 15 may be set so as to satisfy the following relational expression (1). n coal ≦1 / 2n O2 ···(1)

[0037] As an example, Table 1 shows the timing of charging the carbonaceous material 15, the total amount of the carbonaceous material 15 to be charged, and the heat transfer performance ratio with respect to the existing carbonaceous material. Here, the heat transfer performance ratio is a value obtained by normalizing the equivalent cooling capacity when the carbonaceous material 15 is charged by the equivalent cooling capacity of the existing carbonaceous material. The equivalent cooling capacity refers to the relative cooling capacity when the carbonaceous material is charged, assuming that the cooling capacity (degree of reduction in the temperature of the molten pig iron) when the iron scrap 14 is charged is 1. Here, the existing carbonaceous material is amorphous graphite. Figure 3 is a graph showing an estimated value of the change in carbon concentration during blowing when the carbonaceous material 15 is charged. Note that the estimation of the change in carbon concentration is performed without taking into account the time required for carburization into the molten pig iron. In actual operation, carburization takes time and the change in carbon concentration is gradual, but the condition described above of not taking the time required for carburization into consideration (i.e., carburization proceeds immediately) can be said to be an estimation based on conditions where the change in carbon concentration is more severe than in the packaging industry.

[0038] [Table 1]

[0039] In Table 1, in Comparative Example 1, 3 t (tons) of carbonaceous material 15 was charged during dephosphorization blowing, and 5 t of carbonaceous material 15 was further charged before decarbonization blowing. As shown in Figure 1, when oxygen gas injection is started, the carbon concentration in the molten pig iron decreases. Then, when 3 tons of carbonaceous material 15 is charged at once (see the arrow in the figure), the carbon concentration rises to about 4.5%. Furthermore, when 5 tons of carbonaceous material 15 is charged at once (see the arrow in the figure), the carbon concentration rises to about 5.5%. In other words, by charging the carbonaceous material 15 at once, the carbon concentration in the molten pig iron exceeds the saturated carbon concentration. As shown in Table 1, in Comparative Example 1, the heat transfer performance ratio relative to the existing carbonaceous material is -0.3, which indicates that charging the carbonaceous material 15 does not have a heat transfer effect on the molten pig iron.

[0040] In addition, in Table 1, in Comparative Example 2, 3 tons of carbonaceous material 15 was charged at once before dephosphorization blowing. As shown in Figure 1, the carbon concentration in the molten pig iron is about 5.5% at the start of oxygen gas injection. In other words, by charging the carbon material 15 all at once, the carbon concentration in the molten pig iron exceeds the saturated carbon concentration. Then, the carbon concentration in the molten pig iron decreases due to the injection of oxygen gas. As shown in Table 1, in Comparative Example 2, the heat transfer performance ratio relative to the existing carbon material is -0.1, which indicates that charging the carbon material 15 does not have a heat transfer effect on the molten pig iron.

[0041] In Table 1, in Comparative Example 3, 6 t of carbonaceous material 15 was charged before decarbonization blowing, and 2 t of carbonaceous material 15 was further charged during decarbonization blowing. <c>As shown in Fig. 1, when oxygen gas injection is started, the carbon concentration in the molten pig iron decreases. Then, when 6 tons of carbonaceous material 15 is charged at once (see the arrow in the figure), the carbon concentration rises to about 5%. Furthermore, when 2 tons of carbonaceous material 15 is charged at once (see the arrow in the figure), the carbon concentration rises again to about 5%. As shown in Table 1, in Comparative Example 3, the heat transfer performance ratio to the existing carbonaceous material is 0, which indicates that charging the carbonaceous material 15 does not provide a sufficient heat transfer effect to the molten pig iron.

[0042] In Table 1, in Example 1, 7.5 t of carbonaceous material 15 was charged during decarbonization blowing. <d>As shown in Fig. 1, a total amount of 7.5 tons was charged in six separate charges (see arrows in the figure). The amount charged in each charge was set so as not to exceed the saturated carbon concentration. Therefore, even when the carbonaceous material 15 was charged, the carbon concentration increased only to about 3%. As shown in Table 1, in Example 1, the heat transfer performance ratio to the existing carbonaceous material was 0.9, and the charging of the carbonaceous material 15 provided a sufficient heat transfer effect to the molten iron.

[0043] In addition, in Table 1, in Example 2, 8 t of carbonaceous material 15 was charged during decarbonization blowing. <e>As shown in Fig. 1, a total amount of 8 tons was charged in six separate charges (see arrows in the figure). The amount charged in each charge was set so as not to exceed the saturated carbon concentration. Therefore, even when the carbonaceous material 15 was charged, the carbon concentration increased only to about 1.5%. As shown in Table 1, in Example 2, the heat transfer performance ratio to the existing carbonaceous material was 0.7, and the charging of the carbonaceous material 15 provided a sufficient heat transfer effect to the molten iron.

[0044] Here, by charging the carbonaceous material 15 in the decarburization blowing process, it becomes easier to charge the carbonaceous material 15 within a range that is equal to or less than the carbon saturation amount. As shown in FIG. 3, as the amount of oxygen blown (oxygen flow rate) increases, the carbon concentration in the molten pig iron decreases due to a reaction with oxygen gas. Therefore, the carbon concentration in the molten pig iron tends to be lower in the decarburization process than in the dephosphorization blowing process. Therefore, even if the carbonaceous material 15 is charged and the carbon concentration in the molten pig iron temporarily increases, the carbon concentration is unlikely to exceed the saturated carbon concentration. In other words, the amount of carbonaceous material 15 charged in one go can be increased in the decarburization blowing process, making the charging of the carbonaceous material 15 easier.

[0045] Furthermore, since the dephosphorization blowing process is generally much shorter than the decarbonization blowing process, even if the carbonaceous material 15 is charged, the melting of the carbonaceous material 15 is not completed, and the carbonaceous material 15 that was charged with great care is discharged without fully reacting. Furthermore, since the dephosphorization blowing process is short, it is difficult to secure the working time for charging the carbonaceous material 15. From this perspective, too, it is desirable to charge the carbonaceous material 15 in the decarbonization blowing process after intermediate slag discharge. Of course, the carbonaceous material 15 may also be charged in the dephosphorization blowing process.

[0046] In operation without charging the carbonaceous material 15, the exhaust gas generated in the converter 2 is discharged through a duct 8 covering the furnace throat 3. In this case, the amount of exhaust gas that can be discharged is determined by the air flow rate per unit time in the suction device that constitutes the exhaust gas system (not shown), the opening area and distance of the exhaust path, the rotation speed of the suction fan, the damper opening, etc. For example, the amount of exhaust gas that can be normally discharged is, for example, 2000 Nm 3 / min. On the other hand, when charging the carbonaceous material 15 into the converter 2, if a large amount of the carbonaceous material 15 is charged at once, the volatile components contained in the carbonaceous material 15 volatilize, increasing the volume of exhaust gas. As a result, the exhaust gas that cannot be sucked into the exhaust gas system of the refining equipment 1 is blown out of the furnace together with dust and volatile gas. For example, exhaust gas may blow out from the gap between the cover (also called a skirt) that covers the top of the converter 2 and the furnace body. Such unintended blowing of exhaust gas out of the furnace poses environmental risks such as dust generation and disaster prevention risks such as flame ejection.

[0047] Therefore, the inventors have made extensive studies and have come up with the idea of ​​not charging a large amount of the carbonaceous material 15 at once, but setting the amount of the carbonaceous material 15 to be charged per unit time in relation to the amount of exhaust gas that can be discharged in the refining equipment 1. For example, if the amount of exhaust gas that can be discharged in the refining equipment 1 when the carbonaceous material 15 is not charged is 2000 Nm 3 / min. And, due to the exhaust gas generated by charging the carbonaceous material 15, 20% (400 Nm 3 / min), it is assumed that an additional discharge of exhaust gas equivalent to 1000 kJ / min is required. In other words, the charging amount of the carbonaceous material 15 is set so that the amount of gas generated from the volatile components of the carbonaceous material 15 is kept to about 20% of the amount that can be normally discharged. The idea behind this setting condition is that in order to reliably charge the carbonaceous material 15 into the furnace at the charging timing of the carbonaceous material 15, the oxygen supply rate is reduced to the extent that the extension of the blowing time is suppressed to a minimum, and the amount of gas generated from the volatile components corresponds to the exhaust gas margin due to the reduced amount of oxygen supply.

[0048] Here, the inventors have investigated the gases generated from the volatile components contained in the carbonaceous material 15, including benzene (C6H6) and butane (C4H 10 The inventors then defined the amount of gas generated by the complete combustion of benzene and butane as the amount of gas generated from the volatile components. Here, benzene and butane are completely combusted according to the following reaction formula:

[0049] C6H6+9 / 2O2=6CO+3H2O C4H 10 +9 / 2O2=4CO+5H2O

[0050] Based on the above reaction formula, the amount of exhaust gas generated per minute relative to the amount of carbonaceous material 15 fed is calculated as shown in Figure 4. As shown in Figure 4, the upper limit of the amount of gas that can be emitted due to the carbonaceous material 15 is 400 Nm3. 3 The charging amount of the carbonaceous material 15 at this rate is 0.57 t / min. On the other hand, according to the results of a melting test of the carbonaceous material 15 conducted under conditions simulating those of the converter 2, when 1.5 t of the carbonaceous material 15 is charged, the melting completion time is about 3 minutes. In other words, the carbonaceous material 15 is melted in the furnace at a rate of 0.5 t per minute. Therefore, the charging amount of the carbonaceous material 15 per unit time (0.57 t / min), which is set in accordance with the upper limit of the amount of exhaust gas that can be discharged in the refining equipment 1, is consistent with the melting rate obtained from the test results. In other words, even if the carbonaceous material 15 is charged within the range of the amount of exhaust gas that can be discharged, the carbonaceous material 15 is sufficiently melted in the converter 2.

[0051] As shown in FIG. 5, after the first charging, the melting of the carbonaceous material 15 is completed. As described above, when 1.5 t of carbonaceous material is charged in one charging, it takes approximately 3 minutes from charging to the completion of melting. That is, the condition of the charging amount of the carbonaceous material 15 per unit time of 0.57 t / min, which is set in accordance with the upper limit of the dischargeable flue gas generation amount, is satisfied. Therefore, even if flue gas is generated, it is an amount of flue gas that can be discharged. Thereafter, the second charging is performed, and after a while, the melting of the carbonaceous material 15 is completed. Furthermore, the third charging is performed, and after a while, the melting of the carbonaceous material 15 is completed. Each charging satisfies the condition of the charging amount of the carbonaceous material 15 per unit time described above, and the amount of flue gas is a dischargeable amount. Note that, although an example in which the carbonaceous material is charged in three separate steps has been described here, this is merely an example. Of course, two or more chargings may be performed as long as the amount of flue gas after one charging does not exceed the above-mentioned range.

[0052] More specifically, the amount of the biomass-derived carbonaceous material 15 charged each time can be set to satisfy the following conditional expression (2).

[0053]

number

[0054] Where V is the amount of exhaust gas that can be emitted due to carbonaceous materials, M coal : Amount of carbon material charged at one time (g), m gas : the molecular weight of the volatile gas generated from the carbonaceous material, C: the molar ratio of the exhaust gas to the volatile gas when the volatile gas is completely burned, and D: the volatile content in the carbonaceous material.

[0055] In addition, V = r V ext r: Exhaust gas increase coefficient due to charging of carbonaceous material, V ext : The amount of exhaust gas that can be emitted per unit time in the refining facility (Nm 3 / h). r can be set appropriately depending on the type and state of the carbonaceous material 15, but the basic concept is that it is the reduction rate of the exhaust gas amount relative to the maximum oxygen supply amount at the timing of charging the carbonaceous material for the decarburization reaction (2C + O2 = 2CO). For example, r = 0.05 to 0.40.

[0056] Figure 6 shows the change in furnace pressure depending on the amount of carbonaceous material charged per charge. The carbonaceous material 15 is charged under the condition of 0.57 t / min, which is the amount of carbonaceous material 15 charged per unit time, set in accordance with the upper limit of the amount of exhaust gas that can be discharged. As a result, even when the carbonaceous material 15 is charged, the exhaust gas can be appropriately discharged outside the furnace, and the change in furnace pressure is suppressed. Specifically, if the critical furnace pressure change value exceeds 1, there is a risk of flames erupting from the top of the smoke barrier installed in the converter 2 or sparks flying. In the example shown in Figure 6, the critical furnace pressure change value is 1 or less, and the occurrence of events such as flames erupting as described above is suppressed.

[0057] For example, in the approximation line (straight line) shown in Figure 6, the critical furnace pressure change value corresponding to a carbonaceous material charging amount of 1.5 t / cycle has a margin of 0.35 t / cycle up to the critical furnace pressure change value of 1, which is the value that can suppress gas blowout. In the experimental results shown in Figure 6, the oxygen supply amount per unit time was set under conditions that were lower than those under actual conditions, so there is a margin in the furnace pressure change value. However, even taking into account the oxygen supply amount equivalent to 0.35 t / cycle, which is a margin, it has been confirmed through calculations that the exhaust gas due to carbonaceous material charging remains within a predetermined range.

[0058] Next, the charging step of the carbonaceous materials 15 according to this embodiment will be described with reference to FIG. 7. FIG. 7 is a flowchart of the charging step according to this embodiment. As shown in FIG. 7, first, charging conditions for the carbonaceous materials 15 are set (ST12). For example, the charging conditions are the amount of carbonaceous materials 15 charged at one time and the number of times of charging. Also, for example, the charging conditions are the amount of carbonaceous materials 15 charged per unit time.

[0059] Next, the carbonaceous material 15 is charged into the converter 2 according to the charging conditions set in step ST12 (ST14). Then, it is determined whether or not the predetermined number of times of charging has been performed (ST16). If the predetermined number of times of charging has not been performed, the determination is negative, and the charging process returns to step ST14. On the other hand, if the predetermined number of times of charging has been performed, the determination is positive, and the charging process ends.

[0060] As described above, according to the method for producing molten iron of this embodiment, when the biomass-derived carbonaceous material 15 is charged into the converter 2 into which the molten iron 12 and the iron scrap 14 have been charged, the amount of the carbonaceous material 15 to be charged is set based on the releasable amount relative to the exhaust gas generated from the carbonaceous material 15, the molar amount of the volatile gas generated from the carbonaceous material 15, and the molar ratio of the exhaust gas to the volatile gas when the volatile gas is completely combusted. As a result, even if volatile gas is generated from the volatile components in the carbonaceous material 15, the amount is within the releasable amount of the furnace exhaust gas, and therefore unintended emission of the exhaust gas outside the furnace is suppressed.

[0061] Moreover, according to the method for producing molten iron according to the present embodiment, the biomass-derived carbonaceous material 15 is charged into the converter 2 in multiple batches. As a result, even if the amount of the carbonaceous material 15 charged at one time is limited, a sufficient amount of the carbonaceous material 15 can be charged as a total amount of the multiple batches, and the heat transfer effect of the carbonaceous material 15 is ensured.

[0062] Furthermore, according to the method for producing molten iron of this embodiment, the biomass-derived carbonaceous material 15 includes a carbide obtained by carbonizing plant biomass and a binder, and the composition of the carbonaceous material 15 in a dry state is 70% by mass or more of fixed carbon, 25% by mass or less of volatile components, 0.1% by mass or less of sulfur, and the remainder being ash. As a result, even if the carbonaceous material 15 contains a relatively large amount of volatile components, even if volatile gases are generated from the volatile components in the carbonaceous material 15, the amount is within the allowable amount of furnace exhaust gas, and therefore unintended emission of exhaust gas outside the furnace is suppressed.

[0063] Furthermore, according to the method for producing molten iron according to this embodiment, the amount of the carbonaceous materials 15 charged multiple times is set to satisfy the above-mentioned relational expression (2). As a result, compared to the case where a constant amount of the carbonaceous materials 15 is always charged regardless of the molar amount of volatile gas, the dischargeable amount of exhaust gas, etc., it is possible to further prevent the exhaust gas generated by the charging of the carbonaceous materials 15 from being unable to be discharged, and to prevent the unintended emission of the exhaust gas outside the furnace.

[0064] (Variation) In the above embodiment, an example has been described in which, after one charging of the carbonaceous materials 15, the next charging of the carbonaceous materials 15 is performed after the melting of the charged carbonaceous materials 15 is completed. However, the technology of the present disclosure is not limited to this. For example, as shown in FIG. 8 , after one charging of the carbonaceous materials 15 is performed, the charging of the next carbonaceous materials 15 may be started before the melting is completed. In the example shown in FIG. 8 , after the first charging of the carbonaceous materials 15 is performed, the second charging of the carbonaceous materials 15 is performed before the melting of the first charged carbonaceous materials 15 is completed. In this case, the amount of the second charging of the carbonaceous materials 15 is set so that the sum of the amount of flue gas generated by the first charging of the carbonaceous materials 15 and the amount of flue gas generated by the second charging of the carbonaceous materials 15 is within the range of the dischargeable amount of flue gas generation. In addition, from the third time onwards, the carbonaceous materials 15 are inserted before the melting of the carbonaceous materials 15 from the previous charging is completed. The amount of flue gas generated by the carbonaceous materials 15 is within the range of the dischargeable amount of flue gas generation.

[0065] In the above embodiment, an example in which the carbonaceous material 15 is charged into the converter 2 has been described, but the technology of the present disclosure is not limited to this. The present invention may be applied to a case in which the carbonaceous material 15 is charged into an arc furnace.

[0066] In the above embodiment, an example in which the carbonaceous material 15 is charged in multiple batches has been described, but the technology of the present disclosure is not limited to this. Taking into consideration an increase in the carbon saturation amount due to the charging of the carbonaceous material 15 or the amount of volatile gas generated due to the charging of the carbonaceous material 15, the carbonaceous material 15 may be charged in one batch. Furthermore, the carbonaceous material 15 may be charged continuously during the injection of oxygen gas instead of being charged in multiple batches.

[0067] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and applications within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0068] 1. Converter-type refining furnace equipment 2 Converter-type vessel 3 Hearth 4 Oxygen Lance 5 Tuyere 6 Gas inlet pipe 7. Tap 8 Duct 9A, 9B hoppers 10A, 10B Cutting device 11 Shoot 12 Molten iron 13 Molten slag 14. Scrap iron 15 Charcoal material 16 Iron Source< / e> < / d> < / c>

Claims

1. A method for producing molten iron by oxygen blowing after charging molten iron and iron-containing cold material into a furnace, Charging biomass-derived carbonaceous material into the furnace between the start and end of oxygen blowing; and melting the iron-containing cold material using heat generated by oxygen-blown smelting of the molten pig iron, heat of combustion of the biomass-derived carbonaceous material by oxygen in the oxygen-blown smelting, and sensible heat of the molten pig iron; The amount of carbonaceous material charged is set based on the amount of exhaust gas generated from the carbonaceous material that can be discharged, the molar amount of volatile gas generated from the carbonaceous material, and the molar ratio of the exhaust gas to the volatile gas when the volatile gas is completely combusted. A method for producing molten iron.

2. The biomass-derived carbonaceous material is charged into the furnace in multiple batches. The method for producing molten iron according to claim 1.

3. The amount of the biomass-derived carbonaceous material charged each time is set to satisfy the following relationship (A): The method for producing molten iron according to claim 2. [Equation 1] Where V is the amount of exhaust gas that can be emitted from the carbonaceous material, M ｃｏａｌ : Amount of carbonaceous material charged at one time (g), m ｇａｓ C: the molar ratio of exhaust gas to volatile gas when the volatile gas is completely combusted; and D: the volatile content in the carbonaceous material. In addition, V = r V ｅｘｔ r: exhaust gas increase coefficient due to charging of carbonaceous material, V ｅｘｔ : Amount of exhaust gas that can be emitted per unit time in refining equipment (Nm ３ / h).

4. The biomass-derived carbonaceous material includes a carbonized material obtained by carbonizing plant biomass and a binder, The composition of the carbonaceous material in a dry state is 70% by mass or more of fixed carbon, 25% by mass or less of volatile components, 0.1% by mass or less of sulfur, and the remainder is ash. The method for producing molten iron according to any one of claims 1 to 3.

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