WO2021010313A1 - Method for producing low carbon ferrochromium - Google Patents

Method for producing low carbon ferrochromium Download PDF

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Publication number
WO2021010313A1
WO2021010313A1 PCT/JP2020/026997 JP2020026997W WO2021010313A1 WO 2021010313 A1 WO2021010313 A1 WO 2021010313A1 JP 2020026997 W JP2020026997 W JP 2020026997W WO 2021010313 A1 WO2021010313 A1 WO 2021010313A1
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Prior art keywords
slag
reaction vessel
gas
carbon ferrochrome
blowing device
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PCT/JP2020/026997
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French (fr)
Japanese (ja)
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博一 杉森
正浩 森
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Ｊｆｅマテリアル株式会社
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Priority to JP2021533033A priority Critical patent/JPWO2021010313A1/ja
Priority to BR112021024012A priority patent/BR112021024012A2/en
Publication of WO2021010313A1 publication Critical patent/WO2021010313A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/10—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals with refining or fluxing agents; Use of materials therefor, e.g. slagging or scorifying agents
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting

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  • the present invention relates to a method for producing low carbon ferrochrome.
  • Low carbon ferrochrome which is an Fe—Cr alloy having a Cr of 60% by mass or more and a C of 0.1% by mass or less, is generally produced by a method of reducing chromium ore with silicon.
  • the so-called Peran method is adopted as a specific manufacturing method.
  • the basic steps of the Peran method are the first step of melting chrome ore and fresh lime in an electric furnace, and the melting raw material (hereinafter referred to as primary slag) melted in the first step in a ladle.
  • primary slag melting raw material
  • It is provided with a second step of producing low-carbon ferrochrome and secondary slag by pouring hot water, charging silicochrome as a reducing agent into the ladle, stirring the mixture, and causing a reduction reaction.
  • the stirring in the second step is usually performed by relaying in which two ladle are prepared and the molten metal of the primary slag containing silicochrome is repeatedly transferred.
  • the present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing low carbon ferrochrome capable of increasing the mass ratio of chasing chromium ore to primary slag and reducing the power intensity. ..
  • one aspect of the present invention is a first step of dissolving ferrochrome ore and fresh lime in an electric furnace, and a melting raw material dissolved in the reaction vessel having a gas bottom blowing device in the first step (hereinafter, The primary slag) is discharged, a reducing agent and a cold material containing a ferrochrome ore containing 10% or more and 100% or less in terms of mass ratio to the primary slag are added, and the gas bottom blowing device is not used.
  • This is a method for producing low carbon ferrochrome, which comprises a second step of producing low carbon ferrochrome and secondary slag by stirring by bottom blowing an active gas.
  • the present invention is based on a new finding that the thermal efficiency, silicon efficiency and reactivity of reduction reaction can be improved by gas bubbling of a reaction vessel having a gas bottom blowing device.
  • the mass ratio of the chasing chromium ore to the primary slag can be increased to 10% or more, and the electric power intensity can be reduced.
  • FIG. 4 (a) shows an example in which a plug is arranged in the center of the bottom of the reaction vessel
  • FIG. 4 (b) shows an example. An example is shown in which the plug is placed around the bottom of the reaction vessel).
  • FIG. 5A is a plan view of the plug of the reaction vessel used in the method for producing low carbon ferrochrome of the present embodiment
  • FIG. 5B is a vertical sectional view of the plug. It is a graph which shows the relationship between the basicity (CaO / SiO 2 ) of the secondary slag and the chromium content (Cr) mass% of the secondary slag in the second step of the method for producing low carbon ferrochrome of this embodiment. It is a process drawing of the conventional method of manufacturing low carbon ferrochrome.
  • FIG. 1 is a process diagram of a method for producing low carbon ferrochrome according to an embodiment of the present invention.
  • FIG. 2 is a diagram showing equipment used in the method for producing low carbon ferrochrome of the present embodiment.
  • a mixture of chromium ore and quicklime as a medium solvent is dissolved in an electric furnace to produce a dissolved raw material (hereinafter referred to as primary slag).
  • the first step (S1) is provided.
  • chrome ore and quicklime are stored in the hopper 4.
  • a fixed electric furnace in which a hot water outlet 1a is provided at a position higher than the bottom of the furnace to form a hot water pool is used.
  • the hot water outlet 1a may be provided on the bottom of the furnace.
  • the reason why the hot water pool is formed is that a stable amount of heat is maintained even when the primary slag is discharged.
  • the primary slag is discharged from the hot water outlet 1a into the reaction vessel 2.
  • the hot water temperature of the primary slag is as high as 1400 ° C. or higher and 2000 ° C. or lower.
  • the auxiliary raw material silicochrome as a reducing agent was preferably 10% or more and 100% or less by mass ratio with respect to the primary slag. Is charged with a cold material containing 15% or more and 65% or less of additional chromium ore, and the amount of recovered siliconochrome required for chromium reduction. Then, as shown in FIG. 2, the reaction vessel 2 is bottom-blown with an inert gas such as Ar gas from the gas bottom-blowing device 2a to stir, and the oxide of the chromium ore is reduced to obtain low-carbon ferrochrome and 2. Generate the next slag. This reduction step is the second step (S2).
  • reaction vessel 2 From the viewpoint of effectively utilizing the heat of reaction of the reduction reaction, it is desirable to charge the reaction vessel 2 in a state where silicochrome and chasing chromium ore are mixed or in a state where silicochrome and chasing chromium ore are laminated in layers. Alternatively, it is desirable to charge silicochrome into the reaction vessel 2 and then charge the additional chromium ore into the reaction vessel 2.
  • the cold material includes dust generated in the electric furnace 1, blowback metal generated in the reaction vessel 2 or the electric furnace 3, GP (subsieving metal) generated in the reaction vessel 2 or the electric furnace 3, in addition to the chasing chromium ore. It may contain at least one of high chromium-containing slag or chromium-containing raw materials generated in the reaction vessel 2 or the electric furnace 3.
  • the recovered silicochrome is the silicochrome recovered in the third step described later, but other silicochrome may also be used.
  • silicon is used as the reducing agent
  • a silicon-based reducing agent such as metallic silicon may be used in addition to silicochrome.
  • an aluminum-based reducing agent such as aluminum or an aluminum alloy
  • a magnesium-based reducing agent such as magnesium or a magnesium alloy
  • a calcium-based reducing agent such as calcium or a calcium alloy
  • a mixture of these reducing agents may be used.
  • the reduction reaction of chromium oxide of chromium ore with silicon proceeds as follows. Cr 2 O 3 +3 / 2Si ⁇ 2Cr + 3/2SiO 2 ... (1)
  • the liberated SiO 2 reacts with quicklime as shown in the following equations (2) and (3) to generate secondary slag.
  • the secondary slag is generated as in the formulas (2) and (3), the amount of free SiO 2 in the formula (1) decreases, and the reduction reaction in the formula (1) proceeds from left to right.
  • the mass ratio of the chased chromium ore to the primary slag can be increased to 10% or more.
  • Silicon efficiency can be improved by gas bubbling of the reaction vessel 2 having the gas bottom blowing device 2a.
  • Silicon efficiency is the ratio of effective reducing silicon (excluding loss silicon such as oxidation loss) that works effectively as a reducing agent, and is the amount of silicon used to reduce the oxide Cr and Fe. / Amount of silicon input).
  • gas bubbling reduces the oxidation loss of silicon due to the contact between air and metal, and the silicon efficiency is improved accordingly.
  • the silicon efficiency in the case of relayed ring is about 80 to 85%, whereas the silicon efficiency in the case of gas bubbling is about 87 to 94%. Therefore, expensive silicon can be reduced.
  • the reactivity can also be improved by gas bubbling of the reaction vessel 2 having the gas bottom blowing device 2a.
  • the activity coefficient of SiO 2 is increased, the reduction reaction of chromium in the formula (1) is less likely to occur, and the (Cr) mass% of the secondary slag is increased.
  • the reduction reaction proceeds by the gas bubbling of the gas bottom blowing device 2a, the (Cr) mass% of the secondary slag can be reduced.
  • advantageous operation can be performed. For example, even if the basicity is lowered to less than 1.65, it is possible to prevent the chromium yield from being lowered.
  • the chromium oxide content (Cr 2 O 3 % by mass) of the secondary slag in the second step (S2) is adjusted to 10.0% by mass or less.
  • the upper limit of the basicity (CaO / SiO 2 ) of the secondary slag is adjusted to be less than 1.65, preferably less than 1.5, and more preferably less than 1.4.
  • the reaction end point temperature (temperature after the reaction is completed) of the low carbon ferrochrome of the reaction vessel 2 and the molten metal of the secondary slag is a high temperature of 1350 ° C. or higher and 1900 ° C. or lower.
  • FIG. 3 is a vertical cross-sectional view of the reaction vessel 2 having the gas bottom blowing device 2a. As shown in FIG. 3, refractories 8 and 9 are applied to the bottom 6a of the iron skin 6 of the reaction vessel 2. A plug 19 of the gas bottom blowing device 2a is arranged at the center of the bottom of the reaction vessel 2. When an inert gas is introduced into the pipe portion 17 of the plug 19, the inert gas is blown into the reaction vessel 2 from the plug 19, and the molten metal in the reaction vessel 2 is agitated, that is, gas bubbling.
  • the reaction of the formula (1) proceeds from the primary slag as described above.
  • the reaction vessel 2 is mainly composed of primary slag.
  • a molten ferrochrome (metal 21) is formed, and the secondary slag 22 is present on the molten ferrochrome (metal 21).
  • the volume ratio of the secondary slag 22: metal 21 is approximately 4: 1.
  • the gas bottom blowing device that blows the inert gas into the bottom of the reaction vessel 2. 2a is used.
  • the plug 19 of the gas bottom blowing device 2a is offset from the center of the bottom of the reaction vessel 2 (eccentricity) as shown in FIG. 4 (b). It is known that it is better to place it at (position) (see, for example, Japanese Patent Application Laid-Open No. 1-177333).
  • FIG. 4B when a large amount of highly viscous secondary slag 22 is present as in the present embodiment, as shown in FIG. 4B, the plug 19 of the gas bottom blowing device 2a is placed at the eccentric position of the bottom of the reaction vessel 2.
  • the side opposite to the side on which the plug 19 is arranged becomes a weakly agitated state, and the undissolved chasing chromium ore 23 remains on the opposite side.
  • FIG. 4A by arranging the plug 19 of the gas bottom blowing device 2a at the center of the bottom of the reaction vessel 2, after rising from the center of the bottom into the reaction vessel 2. , A flow of molten metal is formed radially toward the periphery. Therefore, the inside of the reaction vessel 2 can be uniformly agitated, and the chasing chromium ore can be involved and dissolved.
  • a plurality of plugs may be arranged on a circle centered on the central portion of the bottom of the reaction vessel 2. Even in this way, the inside of the reaction vessel 2 can be uniformly stirred.
  • FIG. 5A is a plan view of the plug 19, and FIG. 5B is a vertical sectional view of the plug 19.
  • the plug 19 includes a truncated cone-shaped main body 11 and a disk-shaped gas pool forming portion 12 provided below the main body 11.
  • a disk-shaped gas pool portion 13 is formed between the main body 11 and the gas pool forming portion 12.
  • a pipe portion 17 is connected to the gas pool forming portion 12.
  • the main body 11 is made of a refractory material containing MgO and / or Al 2 O 3 in order to withstand the high temperature (1350 ° C. or higher and 1900 ° C. or lower) of the molten metal in the reaction vessel 2.
  • the material of the body 11 for example 92 wt% MgO-4 wt% Cr 2 O 3, or 98 wt% Al 2 O 3 -2 wt% MgO.
  • the gas pool forming portion 12 and the pipe portion 17 are made of iron.
  • a plurality of slits 15 for blowing out the inert gas are formed in the main body 11 made of a refractory material.
  • the slit 15 includes a plurality of inner peripheral side slits 15a arranged in a ring shape and a plurality of outer peripheral side slits 15b arranged in a ring shape.
  • the slit 15 extends downward from the upper surface 11a and communicates with the lower gas pool portion 13.
  • the plug 19 is a slit type plug.
  • the slit type plug has excellent erosion resistance, small bubbles at the outlet of the slit, and strong stirring power. Since it is possible to stir, a porous plug may be used.
  • the blowing amount of the plug 19, that is, the stirring gas amount Q (l / min) is set to 5 l / min or more and 1000 l / min or less per 1 ton of the molten metal.
  • 5 l / min ⁇ Q ⁇ 1000 l / min is required from the conditions that the molten metal does not enter the slit 15 of the plug 19 and the gas does not blow through (the gas does not blow through in a straight line without being agitated).
  • 5 l / min ⁇ Q is required. Even if Q> 1000 l / min, there is no effect in further promoting the reduction reaction, and conversely, the molten metal of the low carbon ferrochrome 21 and the slag 22 cools.
  • the agitation gas amount Q is set according to the amount of the chasing chromium ore, and is set to a larger value as the amount of the chasing chromium ore increases.
  • the molten metal of low carbon ferrochrome produced by the reduction reaction is cast into a mold to become a product.
  • the low carbon ferrochrome of the product contains 60% by mass or more of Cr, 1.0% by mass or less of Si, and 0.1% by mass or less of C.
  • the molten metal of the secondary slag produced by the reduction reaction is separated from the molten metal of low carbon ferrochrome and then charged into the electric furnace 3.
  • ferrosilicon as a reducing agent is charged into the electric furnace 3 in which the secondary slag is charged, and the ferrosilicon as a reducing agent is reacted with the chromium oxide remaining in the secondary slag for recovery. Generates silicon chrome and tertiary slag.
  • This step is the third step (S3).
  • Silica stone (SiO 2 ) may be added to the electric furnace 3 in order to adjust the basicity. Further, the electric furnace 3 may be added with chromium oxide-containing solidified slag that has been landfilled in a factory or left in the factory to solidify.
  • the secondary slag produced by the previous operation of low carbon ferrochrome (the secondary slag produced by relaying using two conventional ladle and / or the reaction vessel 2 of the present embodiment is used.
  • the secondary slag produced by the gas bubbling that was present) contains solidified slag and contains chromium oxide.
  • a gas bottom blowing device may be provided in the electric furnace 3.
  • a reaction vessel for blowing an inert gas may be used.
  • the reaction vessel may be a reaction vessel having a gas bottom blowing device or a top-blowing type reaction vessel in which an inert gas is blown from a lance.
  • the gas bottom blowing device provided in the electric furnace 3 or the reaction vessel is arranged in the central portion of the bottom of the electric furnace 3 or the reaction vessel, similarly to the gas bottom blowing device 2a of the reaction vessel 2 in the second step described above. Is desirable.
  • the volume ratio of the slag (secondary slag 22) and metal (low carbon ferrochrome 21) in the second step (S2) is about 4: 1
  • the volume ratio of the slag (tertiary slag) in the third step (S3) is
  • the volume ratio of metal (recovered silicochrome) is about 10: 1.
  • the amount of stirring gas (l / min) per ton of the molten metal in the third step (S3) is changed to the amount of stirring gas per ton of the molten metal in the second step (S2). It is desirable to make it larger than (l / min).
  • a large amount of ferrosilicon as a reducing agent is charged, that is, 1 time or more, preferably 2 times or more the reduction equivalent of chromium oxide, to make a strong reduction, and the chromium oxide content of the tertiary slag. Is reduced to 1.4% by mass or less, preferably 1.0% by mass or less. This is to reduce the hexavalent chromium of the tertiary slag and to improve the chromium yield.
  • the Si content of the recovered silicochrome is 20% by mass or more and 70% by mass or less.
  • ferrosilicon is used as the reducing agent, a silicon-based reducing agent such as metallic silicon may be used in addition to ferrosilicon.
  • an aluminum-based reducing agent such as aluminum or an aluminum alloy
  • a magnesium-based reducing agent such as magnesium or a magnesium alloy
  • a calcium-based reducing agent such as calcium or a calcium alloy
  • a mixture of these reducing agents may be used.
  • the basicity of the tertiary slag is adjusted to less than 1.3, preferably less than 1.2, and even more preferably less than 1.1.
  • the low basicity deprives CaO from the following (4) hexavalent chromium compounds that bind to CaO as formula (CaO ⁇ CrO 3), hexavalent chromium compounds trivalent chromium compound (Cr 2 O 3) It is thought to change. 2 (CaO ⁇ CrO 3 ) + 2SiO 2 ⁇ 2 (CaO ⁇ SiO 2 ) + Cr 2 O 3 + 3 / 2O 2 ... (4)
  • the lower the lower limit of the basicity of the tertiary slag is preferably, but in order to reduce the chromium content of the tertiary slag, it is 0.7 or more, preferably 0.8 or more, and more preferably 0. 9 or more.
  • Table 1 shows the relationship between the basicity of the secondary slag (CaO / SiO 2) and the tertiary slag basicity (CaO / SiO 2).
  • the auxiliary material for adjusting the basicity CaO / SiO 2
  • Table 1 shows the relationship between the basicity of the secondary slag and the basicity of the tertiary slag.
  • the basicity of the secondary slag is less than 1.65
  • the basicity of the tertiary slag can be reduced to less than 1.3.
  • the basicity of the secondary slag is larger than 1.65, the basicity of the tertiary slag exceeds 1.3.
  • the chromium content of the slag is represented by ((Cr) mass%).
  • the chromium oxide content of slag is represented by (Cr 2 O 3 % by mass).
  • An ICP (Inductively Coupled Plasma) emission spectroscopic analysis method is used as a method for quantifying Cr of slag.
  • JIS G1313-1 2012 decomposition by alkaline melting is used for the decomposition of the sample.
  • the basicity of slag (CaO / SiO 2 ) is expressed by the CaO content of slag / SiO 2 content of slag.
  • An ICP (Inductively Coupled Plasma) emission spectroscopic analysis method is used as a method for quantifying Ca and Si of slag. In this analysis method, "JIS G1313-1 2012 decomposition by alkaline melting" is used for the decomposition of the sample.
  • the recovered silicochrome is charged into the reaction vessel 2 together with the auxiliary raw material silicochrome. Since a part of the auxiliary raw material silicochrome is replaced by the recovered silicochrome, the auxiliary raw material silicochrome is reduced.
  • the recovered silicon chrome may be put into the electric furnace 3 or the reaction vessel of the third step (S3) and used as a partial substitute for ferrosilicon.
  • Tertiary slag is used for roadbed materials or fertilizers, or is landfilled in factories.
  • the amount (concentration) of hexavalent chromium eluted from the tertiary slag is 0.05 mg / l or less.
  • the method for producing low-carbon ferrochrome of the present embodiment has been described above. According to the method for producing low-carbon ferrochrome of the present embodiment, the following effects are obtained.
  • the agitated gas amount Q of the gas bottom blowing device 2a is 5 l / min or more per 1 ton of the molten metal, it is possible to prevent the molten metal from entering the slit 15 of the plug 19, and the reduction reaction can proceed smoothly. Further, since the agitated gas amount Q of the gas bottom blowing device 2a is 1000 l / min or less, it is possible to prevent the gas from blowing through (the gas blows out in a straight line without being agitated), and the molten metal of low carbon ferrochrome and the secondary slag is formed. It can prevent cooling.
  • reaction vessel 2 having the gas bottom blowing device 2a Since the reaction vessel 2 having the gas bottom blowing device 2a is used, it is possible to prevent the chromium yield from decreasing even if the basicity of the second step is reduced to less than 1.65. If the basicity of the second step is less than 1.65, the basicity of the tertiary slag in the third step can be reduced to less than 1.3, and hexavalent chromium harmful to the tertiary slag is generated. Can be suppressed.
  • the reaction vessel 2 having the gas bottom blowing device 2a Since the reaction vessel 2 having the gas bottom blowing device 2a is used, even if the mass ratio of the chasing chromium ore to the primary slag is increased to 10% or more, the reaction end point temperature of the molten metal in the reaction vessel 2 is 1350 ° C. or higher and 1900 ° C. or higher. It can be kept at the following high temperatures. Therefore, the operation of the post-process becomes easy.
  • One plug 19 of the gas bottom blowing device 2a is arranged at the center of the bottom of the reaction vessel 2, and / or a plurality of plugs of the gas bottom blowing device 2a are arranged on a circle centered on the center of the bottom of the reaction vessel 2. Since 19 is arranged, the reaction vessel 2 can be uniformly agitated, and the follow-up chrome ore can be easily involved and dissolved.
  • the plug 19 it is desirable to use a slit type plug having excellent erosion resistance and high stirring ability.
  • reaction chrome ore is charged into the reaction vessel 2 in a state where silicochrome and the additional chrome ore are mixed or in a state where the silicochrome and the additional chrome ore are laminated in layers, or after the silicochrome is charged in the reaction vessel 2, the additional chrome ore is added. Since it is charged into the reaction vessel 2, the reaction heat of the reduction reaction can be effectively used for dissolving the chasing chromium ore.
  • Low carbon ferrochrome was produced according to the production process diagram of FIG. Table 2 shows the composition of the chromium ore as the raw material used in this example.
  • the separated secondary slag was received in a reaction vessel, 230 kg of ferrosilicon was charged, and argon gas was bottom-blown into the reaction vessel to stir. Then, the produced tertiary slag and recovered silicochrome were separated to obtain 1930 kg of tertiary slag and 260 kg of recovered silicochrome. This recovered silicochrome was charged into the primary slag together with the auxiliary raw material silicochrome.
  • Table 4 shows the composition of the tertiary slag
  • Table 5 shows the composition of the recovered silicochrome.
  • the electric power intensity is the amount of electric power used per product t, and specifically (primary slag dissolved electric energy / product production amount).
  • Low carbon ferrochrome was produced according to the production process diagram of FIG. As shown in Table 6, the follow-up rate is set to 13% in operation 1, the follow-up rate is set to 21% in operation 2, the follow-up rate is set to 40% in operation 3, and the follow-up rate is set in operation 4.
  • the dressing rate was set to 65%. As shown in Table 6, even if the tracking rate is increased from 13% to 65%, the basicity of the tertiary slag is 1.0, and the generation of hexavalent chromium harmful to the tertiary slag can be suppressed. It was.
  • the power intensity was as low as 2400 Kwh / t or less, and the higher the tracking rate, the more the power intensity could be reduced. (Conventional example)
  • Low carbon ferrochrome was produced according to the production process diagram of FIG.
  • the reduction operation of the primary slag is performed by relaying, the primary slag is not charged with additional chromium ore, and the recovered siliconochrome is recovered from the secondary slag.
  • Table 7 shows the composition of the chromium ore which is the raw material used in the conventional example.
  • the power intensity was as high as 2980 kwh / t.

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Abstract

The present invention provides a method for producing low carbon ferrochromium, said method being capable of reducing the electric power consumption rate by increasing the mass ratio of additionally charged chromium ore with respect to a primary slag. A method for producing low carbon ferrochromium according to the present invention is provided with: a first step (S1) wherein chromium ore and quick lime are melted in an electric furnace; and a second step (S2) wherein a molten staring material (hereinafter referred to as a primary slag) melted in the first step (S1) is discharged into a reaction container that has a gas bottom-blowing device, and a reducing agent and a cold charge that contains additional chromium ore at a mass ratio of from 10% to 100% relative to the primary slag are charged into the reaction container, so that low carbon ferrochromium and a secondary slag are produced by stirring the materials by bottom-blowing an inert gas from the gas bottom-blowing device.

Description

低炭素フェロクロムの製造方法Method for producing low carbon ferrochrome
　本発明は、低炭素フェロクロムの製造方法に関する。 The present invention relates to a method for producing low carbon ferrochrome.
　Ｃｒ６０質量％以上、Ｃ０．１質量％以下のＦｅ－Ｃｒ合金である低炭素フェロクロムは、一般に、クロム鉱石をシリコンで還元する方法によって製造されている。その具体的な製造方法としては、所謂ペラン法が採用されている。図７に示すように、ペラン法の基本的工程は、クロム鉱石と生石灰を電気炉で溶解する第１工程と、第１工程で溶解した溶解原料（以下、１次スラグという）を取鍋に出湯し、この取鍋内に還元剤としてのシリコクロムを装入して攪拌し、還元反応を行わせて、低炭素フェロクロムと２次スラグを生成する第２工程と、を備える。第２工程での攪拌は、通常、２基の取鍋を用意して、シリコクロムを含んだ１次スラグの溶湯の移し替えを繰り返し行うリレードリングによってなされる。 Low carbon ferrochrome, which is an Fe—Cr alloy having a Cr of 60% by mass or more and a C of 0.1% by mass or less, is generally produced by a method of reducing chromium ore with silicon. The so-called Peran method is adopted as a specific manufacturing method. As shown in FIG. 7, the basic steps of the Peran method are the first step of melting chrome ore and fresh lime in an electric furnace, and the melting raw material (hereinafter referred to as primary slag) melted in the first step in a ladle. It is provided with a second step of producing low-carbon ferrochrome and secondary slag by pouring hot water, charging silicochrome as a reducing agent into the ladle, stirring the mixture, and causing a reduction reaction. The stirring in the second step is usually performed by relaying in which two ladle are prepared and the molten metal of the primary slag containing silicochrome is repeatedly transferred.
　クロム鉱石をシリコンで還元する上記の還元反応は、発熱反応である。従来の低炭素フェロクロムの製造方法においては、反応熱を有効に利用するため、冷材であるクロム鉱石を取鍋に追加装入し、この追装クロム鉱石を取鍋内で溶解させることで、電力原単位を低減させ、生産性を向上させている（特許文献１参照）。 The above reduction reaction of reducing chrome ore with silicon is an exothermic reaction. In the conventional method for producing low-carbon ferrochrome, in order to effectively utilize the heat of reaction, chrome ore, which is a cold material, is additionally charged into the ladle, and this additional chromium ore is melted in the ladle. The power intensity is reduced and the productivity is improved (see Patent Document 1).
特開平１－２２５７４３号公報Japanese Unexamined Patent Publication No. 1-225743
　しかし、２基の取鍋で溶湯の移し替えを行う従来の低炭素フェロクロムの製造方法においては、１次スラグに対する追装クロム鉱石の質量比（追装クロム鉱石の質量／１次スラグの質量）をせいぜい７～９％までしか上げることができないという課題がある。 However, in the conventional method for producing low-carbon ferrochrome in which the molten metal is transferred in two ladle, the mass ratio of the chasing chromium ore to the primary slag (mass of the chasing chromium ore / mass of the primary slag). There is a problem that it can only be raised to 7-9% at most.
　本発明は、上記の課題を鑑みてなされたものであり、１次スラグに対する追装クロム鉱石の質量比を上げ、電力原単位を低減できる低炭素フェロクロムの製造方法を提供することを目的とする。 The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing low carbon ferrochrome capable of increasing the mass ratio of chasing chromium ore to primary slag and reducing the power intensity. ..
　上記課題を解決するために、本発明の一態様は、クロム鉱石と生石灰を電気炉で溶解する第１工程と、ガス底吹き装置を有する反応容器に前記第１工程で溶解した溶解原料（以下、１次スラグという）を出湯し、還元剤と前記１次スラグに対して質量比で１０％以上１００％以下の追装クロム鉱石を含有する冷材を添加し、前記ガス底吹き装置から不活性ガスを底吹きすることにより撹拌して、低炭素フェロクロムと２次スラグを生成させる第２工程と、を備える低炭素フェロクロムの製造方法である。 In order to solve the above problems, one aspect of the present invention is a first step of dissolving ferrochrome ore and fresh lime in an electric furnace, and a melting raw material dissolved in the reaction vessel having a gas bottom blowing device in the first step (hereinafter, The primary slag) is discharged, a reducing agent and a cold material containing a ferrochrome ore containing 10% or more and 100% or less in terms of mass ratio to the primary slag are added, and the gas bottom blowing device is not used. This is a method for producing low carbon ferrochrome, which comprises a second step of producing low carbon ferrochrome and secondary slag by stirring by bottom blowing an active gas.
　本発明は、ガス底吹き装置を有する反応容器のガスバブリングにより熱効率、シリコン効率及び還元反応の反応性を向上させることができるという新たな知見に基づくものである。本発明によれば、ガス底吹き装置を有する反応容器を用いることで、１次スラグに対する追装クロム鉱石の質量比を１０％以上に上げることができ、電力原単位を低減できる。 The present invention is based on a new finding that the thermal efficiency, silicon efficiency and reactivity of reduction reaction can be improved by gas bubbling of a reaction vessel having a gas bottom blowing device. According to the present invention, by using a reaction vessel having a gas bottom blowing device, the mass ratio of the chasing chromium ore to the primary slag can be increased to 10% or more, and the electric power intensity can be reduced.
本発明の一実施形態の低炭素フェロクロムの製造方法の工程図である。It is a process drawing of the manufacturing method of the low carbon ferrochrome of one Embodiment of this invention. 本実施形態の低炭素フェロクロムの製造方法で用いられる全体設備を示す図である。It is a figure which shows the whole equipment used in the manufacturing method of low carbon ferrochrome of this embodiment. 本実施形態の低炭素フェロクロムの製造方法で用いられる反応容器の縦断面図である。It is a vertical sectional view of the reaction vessel used in the method for producing low carbon ferrochrome of this embodiment. 本実施形態の低炭素フェロクロムの製造方法で用いられる反応容器の縦断面図である（図４（ａ）はプラグを反応容器の底部の中央部に配置した例を示し、図４（ｂ）はプラグを反応容器の底部の周辺に配置した例を示す）。It is a vertical cross-sectional view of a reaction vessel used in the method for producing low carbon ferrochrome of this embodiment (FIG. 4 (a) shows an example in which a plug is arranged in the center of the bottom of the reaction vessel, and FIG. 4 (b) shows an example. An example is shown in which the plug is placed around the bottom of the reaction vessel). 図５（ａ）は本実施形態の低炭素フェロクロムの製造方法で用いられる反応容器のプラグの平面図であり、図５（ｂ）はプラグの縦断面図である。FIG. 5A is a plan view of the plug of the reaction vessel used in the method for producing low carbon ferrochrome of the present embodiment, and FIG. 5B is a vertical sectional view of the plug. 本実施形態の低炭素フェロクロムの製造方法の第２工程における２次スラグの塩基度（ＣａＯ／ＳｉＯ２）と２次スラグのクロム含有率（Ｃｒ）質量％との関係を示すグラフである。It is a graph which shows the relationship between the basicity (CaO / SiO 2 ) of the secondary slag and the chromium content (Cr) mass% of the secondary slag in the second step of the method for producing low carbon ferrochrome of this embodiment. 従来の低炭素フェロクロムの製造方法の工程図である。It is a process drawing of the conventional method of manufacturing low carbon ferrochrome.
　以下、添付図面に基づいて、本発明の実施形態の低炭素フェロクロムの製造方法を詳細に説明する。ただし、本発明の低炭素フェロクロムの製造方法は種々の形態で具体化することができ、本明細書に記載される実施形態に限定されるものではない。本実施形態は、明細書の開示を十分にすることによって、当業者が発明を十分に理解できるようにする意図をもって提供されるものである。 Hereinafter, the method for producing low carbon ferrochrome according to the embodiment of the present invention will be described in detail based on the attached drawings. However, the method for producing a low-carbon ferrochrome of the present invention can be embodied in various forms, and is not limited to the embodiments described in the present specification. The present embodiment is provided with the intention of allowing those skilled in the art to fully understand the invention by adequately disclosing the specification.
　図１は、本発明の一実施形態の低炭素フェロクロムの製造方法の工程図である。図２は、本実施形態の低炭素フェロクロムの製造方法で用いられる設備を示す図である。 FIG. 1 is a process diagram of a method for producing low carbon ferrochrome according to an embodiment of the present invention. FIG. 2 is a diagram showing equipment used in the method for producing low carbon ferrochrome of the present embodiment.
　図１に示すように、本実施形態の低炭素フェロクロムの製造方法は、クロム鉱石と媒溶剤である生石灰の混合物を電気炉内で溶解させて溶解原料（以下、１次スラグという）を生成する第１工程（Ｓ１）を備える。 As shown in FIG. 1, in the method for producing low carbon ferrochrome of the present embodiment, a mixture of chromium ore and quicklime as a medium solvent is dissolved in an electric furnace to produce a dissolved raw material (hereinafter referred to as primary slag). The first step (S1) is provided.
　図２に示すように、クロム鉱石と生石灰は、ホッパ４に貯蔵される。電気炉１には、炉底より高い位置に出湯口１ａを設けて湯溜まりを形成した固定型電気炉を用いる。出湯口１ａを炉底に設けてもよい。湯溜まりを形成するのは、１次スラグを出湯しても安定した熱量を保持するためである。１次スラグは、出湯口１ａから反応容器２に出湯される。１次スラグの出湯温度は、１４００℃以上２０００℃以下の高温である。 As shown in FIG. 2, chrome ore and quicklime are stored in the hopper 4. As the electric furnace 1, a fixed electric furnace in which a hot water outlet 1a is provided at a position higher than the bottom of the furnace to form a hot water pool is used. The hot water outlet 1a may be provided on the bottom of the furnace. The reason why the hot water pool is formed is that a stable amount of heat is maintained even when the primary slag is discharged. The primary slag is discharged from the hot water outlet 1a into the reaction vessel 2. The hot water temperature of the primary slag is as high as 1400 ° C. or higher and 2000 ° C. or lower.
　次に、図１、図２に示すように、１次スラグが出湯された反応容器２に、還元剤として副原料のシリコクロム、１次スラグに対して質量比で１０％以上１００％以下、望ましくは１５％以上６５％以下の追装クロム鉱石を含有する冷材、クロム還元に必要な量の回収シリコクロムを装入する。そして、図２に示すように、ガス底吹き装置２ａから反応容器２にＡｒガス等の不活性ガスを底吹きすることにより攪拌し、クロム鉱石の酸化物を還元して、低炭素フェロクロムと２次スラグを生成させる。この還元工程が第２工程（Ｓ２）である。 Next, as shown in FIGS. 1 and 2, in the reaction vessel 2 in which the primary slag was discharged, the auxiliary raw material silicochrome as a reducing agent was preferably 10% or more and 100% or less by mass ratio with respect to the primary slag. Is charged with a cold material containing 15% or more and 65% or less of additional chromium ore, and the amount of recovered siliconochrome required for chromium reduction. Then, as shown in FIG. 2, the reaction vessel 2 is bottom-blown with an inert gas such as Ar gas from the gas bottom-blowing device 2a to stir, and the oxide of the chromium ore is reduced to obtain low-carbon ferrochrome and 2. Generate the next slag. This reduction step is the second step (S2).
　還元反応の反応熱を有効に利用するという観点から、シリコクロムと追装クロム鉱石を混合した状態で若しくはシリコクロムと追装クロム鉱石を層状に積層した状態で反応容器２に装入するのが望ましく、又はシリコクロムを反応容器２に装入した後、追装クロム鉱石を反応容器２に装入するのが望ましい。 From the viewpoint of effectively utilizing the heat of reaction of the reduction reaction, it is desirable to charge the reaction vessel 2 in a state where silicochrome and chasing chromium ore are mixed or in a state where silicochrome and chasing chromium ore are laminated in layers. Alternatively, it is desirable to charge silicochrome into the reaction vessel 2 and then charge the additional chromium ore into the reaction vessel 2.
　冷材には、追装クロム鉱石の他、電気炉１で発生するダスト、反応容器２又は電気炉３で発生する吹き返しメタル、反応容器２又は電気炉３で発生するＧＰ（篩下メタル）、反応容器２又は電気炉３で発生する高クロム含有スラグ、又はクロム含有原料の少なくとも一つを含んでもよい。 The cold material includes dust generated in the electric furnace 1, blowback metal generated in the reaction vessel 2 or the electric furnace 3, GP (subsieving metal) generated in the reaction vessel 2 or the electric furnace 3, in addition to the chasing chromium ore. It may contain at least one of high chromium-containing slag or chromium-containing raw materials generated in the reaction vessel 2 or the electric furnace 3.
　回収シリコクロムは、後述する第３工程で回収されたシリコクロムであるが、それ以外のシリコクロムでもよい。また、還元剤にシリコクロムを用いているが、シリコクロムの他に金属ケイ素等のシリコン系還元剤を用いてもよい。また、シリコン系還元剤の他にアルミ若しくはアルミ合金等のアルミニウム系還元剤、マグネシウム若しくはマグネシウム合金等のマグネシウム系還元剤、又はカルシウム若しくはカルシウム合金等のカルシウム系還元剤を用いてもよい。さらに、これらの還元剤の混合物を用いてもよい。 The recovered silicochrome is the silicochrome recovered in the third step described later, but other silicochrome may also be used. Further, although silicon is used as the reducing agent, a silicon-based reducing agent such as metallic silicon may be used in addition to silicochrome. Further, in addition to the silicon-based reducing agent, an aluminum-based reducing agent such as aluminum or an aluminum alloy, a magnesium-based reducing agent such as magnesium or a magnesium alloy, or a calcium-based reducing agent such as calcium or a calcium alloy may be used. Further, a mixture of these reducing agents may be used.
　反応容器２内において、クロム鉱石の酸化クロムとシリコンとの還元反応は以下のように進む。
　Ｃｒ２Ｏ３＋３／２Ｓｉ→２Ｃｒ＋３／２ＳｉＯ２…（１）
　ここで、遊離したＳｉＯ２は、以下の（２）（３）式のように生石灰と反応し、２次スラグが生成される。
　ＣａＯ＋ＳｉＯ２→ＣａＯ・ＳｉＯ２…（２）
　２ＣａＯ＋ＳｉＯ２→２ＣａＯ・ＳｉＯ２…（３）
　（２）（３）式のように２次スラグが生成されると、（１）式の遊離のＳｉＯ２が少なくなり、（１）式の還元反応は左から右に進む。 In the reaction vessel 2, the reduction reaction of chromium oxide of chromium ore with silicon proceeds as follows.
Cr 2 O 3 +3 / 2Si → 2Cr + 3/2SiO 2 … (1)
Here, the liberated SiO 2 reacts with quicklime as shown in the following equations (2) and (3) to generate secondary slag.
CaO + SiO 2 → CaO ・ SiO 2 … (2)
2CaO + SiO 2 → 2CaO ・ SiO 2 … (3)
When the secondary slag is generated as in the formulas (2) and (3), the amount of free SiO 2 in the formula (1) decreases, and the reduction reaction in the formula (1) proceeds from left to right.
　撹拌能力が高いガス底吹き装置２ａを有する反応容器２のガスバブリングにより、以下に説明するように（１）熱効率、（２）シリコン効率、及び（３）還元反応の反応性を向上させることができる。したがって、1次スラグに対する追装クロム鉱石の質量比を１０％以上に上げることができる。 By gas bubbling of the reaction vessel 2 having the gas bottom blowing device 2a having a high stirring ability, (1) thermal efficiency, (2) silicon efficiency, and (3) reactivity of the reduction reaction can be improved as described below. it can. Therefore, the mass ratio of the chased chromium ore to the primary slag can be increased to 10% or more.
　（１）ガス底吹き装置２ａを有する反応容器２のガスバブリングにより還元反応を進めるので、反応容器２の熱損失を小さくすることができる（言い換えれば熱効率を向上させることができる）。 (1) Since the reduction reaction is promoted by gas bubbling of the reaction vessel 2 having the gas bottom blowing device 2a, the heat loss of the reaction vessel 2 can be reduced (in other words, the thermal efficiency can be improved).
　（２）ガス底吹き装置２ａを有する反応容器２のガスバブリングにより、シリコン効率を向上させることができる。シリコン効率は、還元剤として有効に働いている有効還元シリコン（酸化ロス等のロス分のシリコンを除く）の割合であり、（酸化物であるＣｒ分、Ｆｅ分の還元に使用されたシリコン量／投入シリコン量）で表される。ガスバブリングにより、リレードリングに比べて、空気とメタルが接触することによるシリコンの酸化ロスが少なくなり、その分シリコン効率が向上する。リレードリングの場合のシリコン効率が約８０～８５％であるのに対し、ガスバブリングの場合のシリコン効率は約８７～９４％である。このため、高価なシリコンを削減できる。 (2) Silicon efficiency can be improved by gas bubbling of the reaction vessel 2 having the gas bottom blowing device 2a. Silicon efficiency is the ratio of effective reducing silicon (excluding loss silicon such as oxidation loss) that works effectively as a reducing agent, and is the amount of silicon used to reduce the oxide Cr and Fe. / Amount of silicon input). Compared with relaying, gas bubbling reduces the oxidation loss of silicon due to the contact between air and metal, and the silicon efficiency is improved accordingly. The silicon efficiency in the case of relayed ring is about 80 to 85%, whereas the silicon efficiency in the case of gas bubbling is about 87 to 94%. Therefore, expensive silicon can be reduced.
　（３）ガス底吹き装置２ａを有する反応容器２のガスバブリングにより、反応性を向上させることもできる。生石灰を減らし、塩基度を低下させると、ＳｉＯ２の活量係数が増加し、（１）式のクロムの還元反応が起こりにくくなり、２次スラグの（Ｃｒ）質量％が高くなる。しかし、図６に示すように、ガス底吹き装置２ａのガスバブリングによって還元反応が進行するので、２次スラグの（Ｃｒ）質量％を下げられる。２次スラグの（Ｃｒ）質量％を下げられることにより、有利な操業を行なえる。例えば、塩基度を１．６５未満まで下げても、クロム歩留りが低下するのを防止できる。 (3) The reactivity can also be improved by gas bubbling of the reaction vessel 2 having the gas bottom blowing device 2a. When quicklime is reduced and the basicity is lowered, the activity coefficient of SiO 2 is increased, the reduction reaction of chromium in the formula (1) is less likely to occur, and the (Cr) mass% of the secondary slag is increased. However, as shown in FIG. 6, since the reduction reaction proceeds by the gas bubbling of the gas bottom blowing device 2a, the (Cr) mass% of the secondary slag can be reduced. By reducing the (Cr) mass% of the secondary slag, advantageous operation can be performed. For example, even if the basicity is lowered to less than 1.65, it is possible to prevent the chromium yield from being lowered.
　第２工程（Ｓ２）での２次スラグの酸化クロム含有率（Ｃｒ２Ｏ３質量％）は、１０．０質量％以下に調整される。２次スラグの塩基度（ＣａＯ／ＳｉＯ２）の上限は、１．６５未満、望ましくは１．５未満、さらに望ましくは１．４未満に低く調整される。２次スラグの塩基度を１．６５未満に低くすることで、後述する３次スラグの塩基度を１．３未満に低くし、３次スラグに有害な６価クロムが発生するのを防止するためである。２次スラグの塩基度の下限は、低ければ低いほど好ましいが、第３工程（Ｓ３）での反応性を確保するために、２次スラグの塩基度の下限を１．０以上とする。 The chromium oxide content (Cr 2 O 3 % by mass) of the secondary slag in the second step (S2) is adjusted to 10.0% by mass or less. The upper limit of the basicity (CaO / SiO 2 ) of the secondary slag is adjusted to be less than 1.65, preferably less than 1.5, and more preferably less than 1.4. By lowering the basicity of the secondary slag to less than 1.65, the basicity of the tertiary slag described later is lowered to less than 1.3, and hexavalent chromium harmful to the tertiary slag is prevented from being generated. Because. The lower the lower limit of the basicity of the secondary slag, the more preferable, but in order to secure the reactivity in the third step (S3), the lower limit of the basicity of the secondary slag is set to 1.0 or more.
　反応容器２の低炭素フェロクロムと２次スラグの溶湯の反応終点温度（反応終了後の温度）は、１３５０℃以上１９００℃以下の高温である。 The reaction end point temperature (temperature after the reaction is completed) of the low carbon ferrochrome of the reaction vessel 2 and the molten metal of the secondary slag is a high temperature of 1350 ° C. or higher and 1900 ° C. or lower.
　図３は、ガス底吹き装置２ａを有する反応容器２の縦断面図である。図３に示すように、反応容器２の鉄皮６の底６ａには、耐火物８，９が施される。反応容器２の底部の中央部には、ガス底吹き装置２ａのプラグ１９が配置される。プラグ１９のパイプ部１７に不活性ガスを導入すると、プラグ１９から反応容器２内に不活性ガスが吹き込まれ、反応容器２内の溶湯が攪拌、すなわちガスバブリングされる。 FIG. 3 is a vertical cross-sectional view of the reaction vessel 2 having the gas bottom blowing device 2a. As shown in FIG. 3, refractories 8 and 9 are applied to the bottom 6a of the iron skin 6 of the reaction vessel 2. A plug 19 of the gas bottom blowing device 2a is arranged at the center of the bottom of the reaction vessel 2. When an inert gas is introduced into the pipe portion 17 of the plug 19, the inert gas is blown into the reaction vessel 2 from the plug 19, and the molten metal in the reaction vessel 2 is agitated, that is, gas bubbling.
　第２工程（Ｓ２）の操業は、上記のように１次スラグから（１）式の反応を進行させる。操業の初期では、反応容器２内は１次スラグが主体である。反応の進行とともにフェロクロムの溶湯（メタル２１）が生成し、フェロクロムの溶湯（メタル２１）の上に２次スラグ２２が存在する状態となる。最終的には、２次スラグ２２：メタル２１の体積比は、概ね４：１となる。粘性の高い２次スラグ２２が多量に存在する状態で反応性を高めるためには、撹拌能力を高めることが必要であり、そのために、反応容器２の底部に不活性ガスを吹き込むガス底吹き装置２ａを用いる。 In the operation of the second step (S2), the reaction of the formula (1) proceeds from the primary slag as described above. At the initial stage of operation, the reaction vessel 2 is mainly composed of primary slag. As the reaction progresses, a molten ferrochrome (metal 21) is formed, and the secondary slag 22 is present on the molten ferrochrome (metal 21). Finally, the volume ratio of the secondary slag 22: metal 21 is approximately 4: 1. In order to increase the reactivity in the presence of a large amount of highly viscous secondary slag 22, it is necessary to increase the stirring capacity, and for this purpose, the gas bottom blowing device that blows the inert gas into the bottom of the reaction vessel 2. 2a is used.
　一般に溶融メタルが主体の場合、撹拌効率を高めるためには、図４（ｂ）に示すように、ガス底吹き装置２ａのプラグ１９を反応容器２の底部の中央部からオフセットさせた位置（偏心位置）に配置するのがよいことが知られている（例えば特開平１－１７７３３３号公報参照）。しかし、本実施形態のように、粘性の高い２次スラグ２２が多量に存在する場合、図４（ｂ）に示すように、ガス底吹き装置２ａのプラグ１９を反応容器２の底部の偏心位置に配置すると、プラグ１９を配置した側とは反対側が弱攪拌状態になり、反対側で未溶解の追装クロム鉱石２３が残る。これに対し、図４（ａ）に示すように、ガス底吹き装置２ａのプラグ１９を反応容器２の底部の中央部に配置することで、反応容器２内に底部の中央部から上昇した後、放射状に周辺に向かう溶湯の流れが形成される。このため、反応容器２内を均一に攪拌でき、追装クロム鉱石を巻き込んで溶解することが可能になる。反応容器２の底部の中央部を中心にした円上に複数のプラグを配置してもよい。このようにしても、反応容器２内を均一に攪拌できる。 Generally, when molten metal is the main component, in order to improve the stirring efficiency, the plug 19 of the gas bottom blowing device 2a is offset from the center of the bottom of the reaction vessel 2 (eccentricity) as shown in FIG. 4 (b). It is known that it is better to place it at (position) (see, for example, Japanese Patent Application Laid-Open No. 1-177333). However, when a large amount of highly viscous secondary slag 22 is present as in the present embodiment, as shown in FIG. 4B, the plug 19 of the gas bottom blowing device 2a is placed at the eccentric position of the bottom of the reaction vessel 2. When arranged in, the side opposite to the side on which the plug 19 is arranged becomes a weakly agitated state, and the undissolved chasing chromium ore 23 remains on the opposite side. On the other hand, as shown in FIG. 4A, by arranging the plug 19 of the gas bottom blowing device 2a at the center of the bottom of the reaction vessel 2, after rising from the center of the bottom into the reaction vessel 2. , A flow of molten metal is formed radially toward the periphery. Therefore, the inside of the reaction vessel 2 can be uniformly agitated, and the chasing chromium ore can be involved and dissolved. A plurality of plugs may be arranged on a circle centered on the central portion of the bottom of the reaction vessel 2. Even in this way, the inside of the reaction vessel 2 can be uniformly stirred.
　図５（ａ）はプラグ１９の平面図であり、図５（ｂ）はプラグ１９の縦断面図である。プラグ１９は、円錐台状の本体１１と、本体１１の下部に設けられる円盤状のガス溜り形成部１２と、を備える。本体１１とガス溜り形成部１２との間には、円盤状のガス溜まり部１３が形成される。ガス溜り形成部１２には、パイプ部１７が接続される。本体１１は、反応容器２内の溶湯の高温（１３５０℃以上１９００℃以下）に耐えるために、ＭｇＯ及び／又はＡｌ２Ｏ３を含む耐火物からなる。本体１１の材質は、例えば９２質量％ＭｇＯ－４質量％Ｃｒ２Ｏ３、又は９８質量％Ａｌ２Ｏ３－２質量％ＭｇＯである。ガス溜り形成部１２とパイプ部１７は、鉄製である。 FIG. 5A is a plan view of the plug 19, and FIG. 5B is a vertical sectional view of the plug 19. The plug 19 includes a truncated cone-shaped main body 11 and a disk-shaped gas pool forming portion 12 provided below the main body 11. A disk-shaped gas pool portion 13 is formed between the main body 11 and the gas pool forming portion 12. A pipe portion 17 is connected to the gas pool forming portion 12. The main body 11 is made of a refractory material containing MgO and / or Al 2 O 3 in order to withstand the high temperature (1350 ° C. or higher and 1900 ° C. or lower) of the molten metal in the reaction vessel 2. The material of the body 11, for example 92 wt% MgO-4 wt% Cr 2 O 3, or 98 wt% Al 2 O 3 -2 wt% MgO. The gas pool forming portion 12 and the pipe portion 17 are made of iron.
　図５（ａ）に示すように、耐火物からなる本体１１には、不活性ガスを吹き出す複数のスリット１５が形成される。スリット１５は、リング状に配列される複数の内周側スリット１５ａと、リング状に配列される複数の外周側スリット１５ｂと、を備える。図５（ｂ）に示すように、スリット１５は、上面１１ａから下方向に延びていて、下部のガス溜まり部１３に連通する。 As shown in FIG. 5A, a plurality of slits 15 for blowing out the inert gas are formed in the main body 11 made of a refractory material. The slit 15 includes a plurality of inner peripheral side slits 15a arranged in a ring shape and a plurality of outer peripheral side slits 15b arranged in a ring shape. As shown in FIG. 5B, the slit 15 extends downward from the upper surface 11a and communicates with the lower gas pool portion 13.
　図３に示すように、プラグ１９のパイプ部１７に不活性ガスを導入すると、プラグ１９から反応容器２内に不活性ガスが吹き込まれ、反応容器２内の低炭素フェロクロム２１とスラグ２２の溶湯がすなわちガスバブリングされる。 As shown in FIG. 3, when the inert gas is introduced into the pipe portion 17 of the plug 19, the inert gas is blown into the reaction vessel 2 from the plug 19, and the low carbon ferrochrome 21 and the molten metal of the slag 22 in the reaction vessel 2 are melted. That is, gas bubbling is performed.
　上記のように、プラグ１９はスリット式プラグである。スリット式プラグは、ポーラスプラグに比較して、耐溶損性に優れ、スリットの出口での気泡が小さくて攪拌力が強いという特徴を持つ。なお、攪拌できないことはないので、ポーラスプラグを使用してもよい。 As mentioned above, the plug 19 is a slit type plug. Compared to the porous plug, the slit type plug has excellent erosion resistance, small bubbles at the outlet of the slit, and strong stirring power. Since it is possible to stir, a porous plug may be used.
　プラグ１９の吹き込み量、すなわち攪拌ガス量Ｑ（ｌ／ｍｉｎ）は、溶湯１ｔ当たり５ｌ／ｍｉｎ以上１０００ｌ／ｍｉｎ以下に設定される。プラグ１９のスリット１５に溶湯が浸入しない条件とガスが吹き抜け（攪拌できずに一直線にガスが吹き抜ける）しない条件から、５ｌ／ｍｉｎ≦Ｑ≦１０００ｌ／ｍｉｎが必要である。還元反応をスムーズに進行させるには、５ｌ／ｍｉｎ≦Ｑが必要である。Ｑ＞１０００ｌ／ｍｉｎにしても、それ以上還元反応を進行させるのに効果がなく、逆に低炭素フェロクロム２１とスラグ２２の溶湯が冷却する。攪拌ガス量Ｑは、追装クロム鉱石の量に応じて設定され、追装クロム鉱石の量が多ければ多いほど大きい値に設定される。 The blowing amount of the plug 19, that is, the stirring gas amount Q (l / min) is set to 5 l / min or more and 1000 l / min or less per 1 ton of the molten metal. 5 l / min ≦ Q ≦ 1000 l / min is required from the conditions that the molten metal does not enter the slit 15 of the plug 19 and the gas does not blow through (the gas does not blow through in a straight line without being agitated). In order for the reduction reaction to proceed smoothly, 5 l / min ≦ Q is required. Even if Q> 1000 l / min, there is no effect in further promoting the reduction reaction, and conversely, the molten metal of the low carbon ferrochrome 21 and the slag 22 cools. The agitation gas amount Q is set according to the amount of the chasing chromium ore, and is set to a larger value as the amount of the chasing chromium ore increases.
　再び図１に示すように、還元反応によって生成した低炭素フェロクロムの溶湯は、鋳型に鋳込まれて製品となる。製品の低炭素フェロクロムは、Ｃｒを６０質量％以上、Ｓｉを１．０質量％以下、Ｃを０．１質量％以下含む。一方、還元反応によって生成した２次スラグの溶湯は、低炭素フェロクロムの溶湯から分離された後、電気炉３に装入される。 As shown in FIG. 1 again, the molten metal of low carbon ferrochrome produced by the reduction reaction is cast into a mold to become a product. The low carbon ferrochrome of the product contains 60% by mass or more of Cr, 1.0% by mass or less of Si, and 0.1% by mass or less of C. On the other hand, the molten metal of the secondary slag produced by the reduction reaction is separated from the molten metal of low carbon ferrochrome and then charged into the electric furnace 3.
　次に、図１に示すように、２次スラグが装入された電気炉３に還元剤としてのフェロシリコンを装入し、２次スラグ中に残留している酸化クロムと反応させて、回収シリコクロムと３次スラグを生成させる。この工程が第３工程（Ｓ３）である。電気炉３には、塩基度を調整するために、硅石（ＳｉＯ２）が添加される場合もある。また、電気炉３には、工場に埋め立てられ、又は工場に放置されて固化した酸化クロム含有固化スラグが添加される場合もある。固化スラグは、以前の低炭素フェロクロムの操業で製造された２次スラグ（従来の２基の取鍋を用いたリレードリングによって製造された２次スラグ及び／又は本実施形態の反応容器２を用いたガスバブリングによって製造された２次スラグ）が固化したスラグを含み、酸化クロムを含む。 Next, as shown in FIG. 1, ferrosilicon as a reducing agent is charged into the electric furnace 3 in which the secondary slag is charged, and the ferrosilicon as a reducing agent is reacted with the chromium oxide remaining in the secondary slag for recovery. Generates silicon chrome and tertiary slag. This step is the third step (S3). Silica stone (SiO 2 ) may be added to the electric furnace 3 in order to adjust the basicity. Further, the electric furnace 3 may be added with chromium oxide-containing solidified slag that has been landfilled in a factory or left in the factory to solidify. As the solidified slag, the secondary slag produced by the previous operation of low carbon ferrochrome (the secondary slag produced by relaying using two conventional ladle and / or the reaction vessel 2 of the present embodiment is used. The secondary slag produced by the gas bubbling that was present) contains solidified slag and contains chromium oxide.
　なお、電気炉３にガス底吹き装置を設けてもよい。電気炉３の替わりに、不活性ガスを吹き込む反応容器を使用してもよい。反応容器は、ガス底吹き装置を有する反応容器でも、ランスから不活性ガスを吹き込む上吹き式の反応容器でもよい。電気炉３又は反応容器に設けられるガス底吹き装置は、前述した第２工程の反応容器２のガス底吹き装置２ａと同様に、電気炉３又は反応容器の底部の中央部に配置されるのが望ましい。第２工程（Ｓ２）のスラグ（２次スラグ２２）とメタル（低炭素フェロクロム２１）の体積比は約４：１であるのに対し、第３工程（Ｓ３）のスラグ（３次スラグ）とメタル（回収シリコクロム）の体積比は約１０：１である。第３工程（Ｓ３）の溶湯の攪拌力を高めるために、第３工程（Ｓ３）の溶湯１ｔ当たりの攪拌ガス量（ｌ／ｍｉｎ）を第２工程（Ｓ２）の溶湯１ｔ当たりの攪拌ガス量（ｌ／ｍｉｎ）よりも大きくするのが望ましい。 A gas bottom blowing device may be provided in the electric furnace 3. Instead of the electric furnace 3, a reaction vessel for blowing an inert gas may be used. The reaction vessel may be a reaction vessel having a gas bottom blowing device or a top-blowing type reaction vessel in which an inert gas is blown from a lance. The gas bottom blowing device provided in the electric furnace 3 or the reaction vessel is arranged in the central portion of the bottom of the electric furnace 3 or the reaction vessel, similarly to the gas bottom blowing device 2a of the reaction vessel 2 in the second step described above. Is desirable. The volume ratio of the slag (secondary slag 22) and metal (low carbon ferrochrome 21) in the second step (S2) is about 4: 1, whereas the volume ratio of the slag (tertiary slag) in the third step (S3) is The volume ratio of metal (recovered silicochrome) is about 10: 1. In order to increase the stirring power of the molten metal in the third step (S3), the amount of stirring gas (l / min) per ton of the molten metal in the third step (S3) is changed to the amount of stirring gas per ton of the molten metal in the second step (S2). It is desirable to make it larger than (l / min).
　第３工程（Ｓ３）では、還元剤としてのフェロシリコンを多量、すなわち酸化クロムの還元当量の１倍以上、望ましくは２倍以上装入し、強還元にして、３次スラグの酸化クロム含有率を１．４質量％以下、望ましくは１．０質量％以下まで低減させる。３次スラグの６価クロムを低減させるためであり、クロム歩留りを向上させるためである。回収シリコクロムのＳｉ含有率は、２０質量％以上７０質量％以下である。なお、還元剤にフェロシリコンを用いているが、フェロシリコンの他に金属ケイ素等のシリコン系還元剤を用いてもよい。また、シリコン系還元剤の他にアルミ若しくはアルミ合金等のアルミニウム系還元剤、マグネシウム若しくはマグネシウム合金等のマグネシウム系還元剤、又はカルシウム若しくはカルシウム合金等のカルシウム系還元剤を用いてもよい。さらに、これらの還元剤の混合物を用いてもよい。 In the third step (S3), a large amount of ferrosilicon as a reducing agent is charged, that is, 1 time or more, preferably 2 times or more the reduction equivalent of chromium oxide, to make a strong reduction, and the chromium oxide content of the tertiary slag. Is reduced to 1.4% by mass or less, preferably 1.0% by mass or less. This is to reduce the hexavalent chromium of the tertiary slag and to improve the chromium yield. The Si content of the recovered silicochrome is 20% by mass or more and 70% by mass or less. Although ferrosilicon is used as the reducing agent, a silicon-based reducing agent such as metallic silicon may be used in addition to ferrosilicon. Further, in addition to the silicon-based reducing agent, an aluminum-based reducing agent such as aluminum or an aluminum alloy, a magnesium-based reducing agent such as magnesium or a magnesium alloy, or a calcium-based reducing agent such as calcium or a calcium alloy may be used. Further, a mixture of these reducing agents may be used.
　３次スラグの塩基度は、１．３未満、望ましくは１．２未満、さらに望ましくは１．１未満に低く調整される。低塩基度にすると、以下の（４）式のようにＣａＯと結合する６価クロム化合物（ＣａＯ・ＣｒＯ３）からＣａＯを奪い、６価クロム化合物を３価クロム化合物（Ｃｒ２Ｏ３）に変えると考えられる。
　２（ＣａＯ・ＣｒＯ３）＋２ＳｉＯ２→２（ＣａＯ・ＳｉＯ２）＋Ｃｒ２Ｏ３＋３／２Ｏ２…（４） The basicity of the tertiary slag is adjusted to less than 1.3, preferably less than 1.2, and even more preferably less than 1.1. When the low basicity, deprives CaO from the following (4) hexavalent chromium compounds that bind to CaO as formula (CaO · CrO 3), hexavalent chromium compounds trivalent chromium compound (Cr 2 O 3) It is thought to change.
2 (CaO ・ CrO 3 ) + 2SiO 2 → 2 (CaO ・ SiO 2 ) + Cr 2 O 3 + 3 / 2O 2 … (4)
　ここで、３次スラグの塩基度の下限は、低ければ低いほど好ましいが、３次スラグのクロム含有率を低減するために、０．７以上、望ましくは０．８以上、さらに望ましくは０．９以上とする。 Here, the lower the lower limit of the basicity of the tertiary slag is preferably, but in order to reduce the chromium content of the tertiary slag, it is 0.7 or more, preferably 0.8 or more, and more preferably 0. 9 or more.
　表１は、２次スラグの塩基度（ＣａＯ／ＳｉＯ２）と３次スラグの塩基度（ＣａＯ／ＳｉＯ２）との関係を示す。第３工程（Ｓ３）において塩基度（ＣａＯ／ＳｉＯ２）調整用の副原料を添加しない場合、２次スラグの塩基度と３次スラグの塩基度とには、正の相関関係がある。表１に示すように、２次スラグの塩基度が１．６５未満であれば、３次スラグの塩基度を１．３未満に低減することができる。一方、２次スラグの塩基度が１．６５より大きければ、３次スラグの塩基度が１．３を超えてしまう。
Figure JPOXMLDOC01-appb-T000001
 Table 1 shows the relationship between the basicity of the secondary slag (CaO / SiO 2) and the tertiary slag basicity (CaO / SiO 2). When the auxiliary material for adjusting the basicity (CaO / SiO 2 ) is not added in the third step (S3), there is a positive correlation between the basicity of the secondary slag and the basicity of the tertiary slag. As shown in Table 1, if the basicity of the secondary slag is less than 1.65, the basicity of the tertiary slag can be reduced to less than 1.3. On the other hand, if the basicity of the secondary slag is larger than 1.65, the basicity of the tertiary slag exceeds 1.3.
Figure JPOXMLDOC01-appb-T000001
　スラグの酸化クロム含有率の定量化方法、スラグの塩基度の定量化方法を説明する。スラグの酸化クロム含有率は、スラグのＣｒ含有率を酸化物換算したものである。具体的には、酸化クロムを全量Ｃｒ２Ｏ３として、酸化クロム含有率＝Ｃｒ含有率×１５２／１０４とする。本実施形態のように３次スラグの酸化クロム含有率を１．４質量％以下にすることは、３次スラグのクロム含有率を１．４×１０４／１５２＝０．９６≒１質量％以下にすることを意味する。スラグのクロム含有率は（（Ｃｒ）質量％）で表される。スラグの酸化クロム含有率は（Ｃｒ２Ｏ３質量％）で表される。スラグのＣｒの定量化方法には、ＩＣＰ（Inductively Coupled Plasma）発光分光分析方法を使用する。この分析方法において、試料の分解には「ＪＩＳ　Ｇ１３１３－１　２０１２　アルカリ融解による分解」を援用する。 A method for quantifying the chromium oxide content of slag and a method for quantifying the basicity of slag will be described. The chromium oxide content of slag is obtained by converting the Cr content of slag into an oxide. Specifically, the total amount of chromium oxide is Cr 2 O 3 , and the chromium oxide content = Cr content × 152/104. To reduce the chromium oxide content of the tertiary slag to 1.4% by mass or less as in the present embodiment, the chromium content of the tertiary slag is 1.4 × 104/152 = 0.96 ≈ 1% by mass or less. Means to. The chromium content of the slag is represented by ((Cr) mass%). The chromium oxide content of slag is represented by (Cr 2 O 3 % by mass). An ICP (Inductively Coupled Plasma) emission spectroscopic analysis method is used as a method for quantifying Cr of slag. In this analysis method, "JIS G1313-1 2012 decomposition by alkaline melting" is used for the decomposition of the sample.
　スラグの塩基度（ＣａＯ／ＳｉＯ２）は、スラグのＣａＯ含有率／スラグのＳｉＯ２含有率で表される。スラグのＣａＯ含有率は、スラグのＣａ含有率を酸化物換算したものであり、ＣａＯ含有率＝Ｃａ含有率×５６／４０である。スラグのＳｉＯ２含有率は、スラグのＳｉ含有率を酸化物換算したものであり、ＳｉＯ２含有率＝Ｓｉ含有率×６０／２８である。スラグのＣａとＳｉの定量化方法には、ＩＣＰ（Inductively Coupled Plasma）発光分光分析方法を使用する。この分析方法において、試料の分解には「ＪＩＳ　Ｇ１３１３－１　２０１２　アルカリ融解による分解」を援用する。 The basicity of slag (CaO / SiO 2 ) is expressed by the CaO content of slag / SiO 2 content of slag. The CaO content of the slag is obtained by converting the Ca content of the slag into an oxide, and CaO content = Ca content × 56/40. The SiO 2 content of the slag is obtained by converting the Si content of the slag into an oxide, and SiO 2 content = Si content × 60/28. An ICP (Inductively Coupled Plasma) emission spectroscopic analysis method is used as a method for quantifying Ca and Si of slag. In this analysis method, "JIS G1313-1 2012 decomposition by alkaline melting" is used for the decomposition of the sample.
　再び図１に示すように、回収シリコクロムは、副原料シリコクロムと共に反応容器２に装入される。副原料シリコクロムの一部が回収シリコクロムによって代替されるので、副原料シリコクロムが低減される。回収シリコクロムを第３工程（Ｓ３）の電気炉３又は反応容器に投入し、フェロシリコンの一部代替として利用してもよい。３次スラグは、路盤材又は肥料に使用され、又は工場に埋め立てられる。３次スラグの６価クロム溶出量（濃度）は、０．０５ｍｇ／ｌ以下である。 As shown in FIG. 1 again, the recovered silicochrome is charged into the reaction vessel 2 together with the auxiliary raw material silicochrome. Since a part of the auxiliary raw material silicochrome is replaced by the recovered silicochrome, the auxiliary raw material silicochrome is reduced. The recovered silicon chrome may be put into the electric furnace 3 or the reaction vessel of the third step (S3) and used as a partial substitute for ferrosilicon. Tertiary slag is used for roadbed materials or fertilizers, or is landfilled in factories. The amount (concentration) of hexavalent chromium eluted from the tertiary slag is 0.05 mg / l or less.
　以上に本実施形態の低炭素フェロクロムの製造方法を説明した。本実施形態の低炭素フェロクロムの製造方法によれば、以下の効果を奏する。 The method for producing low-carbon ferrochrome of the present embodiment has been described above. According to the method for producing low-carbon ferrochrome of the present embodiment, the following effects are obtained.
　ガス底吹き装置２ａを有する反応容器２のガスバブリングにより（１）熱効率、（２）シリコン効率及び（３）還元反応の反応性を向上させることができる。したがって、追装クロム鉱石の量を１０％以上に上げ、電力原単位を低減できる。 By gas bubbling of the reaction vessel 2 having the gas bottom blowing device 2a, (1) thermal efficiency, (2) silicon efficiency and (3) reactivity of the reduction reaction can be improved. Therefore, the amount of chasing chrome ore can be increased to 10% or more, and the power intensity can be reduced.
　ガス底吹き装置２ａの攪拌ガス量Ｑが溶湯１ｔ当たり５ｌ／ｍｉｎ以上であるので、プラグ１９のスリット１５に溶湯が浸入するのを防止でき、還元反応をスムーズに進行させることができる。また、ガス底吹き装置２ａの攪拌ガス量Ｑが１０００ｌ／ｍｉｎ以下であるので、ガスが吹き抜け（攪拌できずに一直線にガスが吹き抜ける）のを防止でき、低炭素フェロクロムと２次スラグの溶湯が冷却するのを防止できる。 Since the agitated gas amount Q of the gas bottom blowing device 2a is 5 l / min or more per 1 ton of the molten metal, it is possible to prevent the molten metal from entering the slit 15 of the plug 19, and the reduction reaction can proceed smoothly. Further, since the agitated gas amount Q of the gas bottom blowing device 2a is 1000 l / min or less, it is possible to prevent the gas from blowing through (the gas blows out in a straight line without being agitated), and the molten metal of low carbon ferrochrome and the secondary slag is formed. It can prevent cooling.
　ガス底吹き装置２ａを有する反応容器２を使用するので、第２工程の塩基度を１．６５未満まで下げても、クロム歩留りが低下するのを防止できる。第２工程の塩基度が１．６５未満まであれば、第３工程の３次スラグの塩基度を１．３未満に低減することができ、３次スラグに有害な６価クロムが発生するのを抑制することができる。 Since the reaction vessel 2 having the gas bottom blowing device 2a is used, it is possible to prevent the chromium yield from decreasing even if the basicity of the second step is reduced to less than 1.65. If the basicity of the second step is less than 1.65, the basicity of the tertiary slag in the third step can be reduced to less than 1.3, and hexavalent chromium harmful to the tertiary slag is generated. Can be suppressed.
　ガス底吹き装置２ａを有する反応容器２を使用するので、１次スラグに対する追装クロム鉱石の質量比を１０％以上に上げても、反応容器２の溶湯の反応終点温度を１３５０℃以上１９００℃以下の高温に保つことができる。このため、後工程の操業が容易になる。 Since the reaction vessel 2 having the gas bottom blowing device 2a is used, even if the mass ratio of the chasing chromium ore to the primary slag is increased to 10% or more, the reaction end point temperature of the molten metal in the reaction vessel 2 is 1350 ° C. or higher and 1900 ° C. or higher. It can be kept at the following high temperatures. Therefore, the operation of the post-process becomes easy.
　反応容器２の底部の中央部にガス底吹き装置２ａの１つのプラグ１９を配置し、及び／又は反応容器２の底部の中央部を中心にした円上にガス底吹き装置２ａの複数のプラグ１９を配置するので、反応容器２を均一に攪拌でき、追装クロム鉱石を巻き込んで溶解し易い。 One plug 19 of the gas bottom blowing device 2a is arranged at the center of the bottom of the reaction vessel 2, and / or a plurality of plugs of the gas bottom blowing device 2a are arranged on a circle centered on the center of the bottom of the reaction vessel 2. Since 19 is arranged, the reaction vessel 2 can be uniformly agitated, and the follow-up chrome ore can be easily involved and dissolved.
　プラグ１９には、耐溶損性に優れ、攪拌能力も高いスリット式プラグを用いるのが望ましい。 For the plug 19, it is desirable to use a slit type plug having excellent erosion resistance and high stirring ability.
　シリコクロムと追装クロム鉱石を混合した状態で若しくはシリコクロムと追装クロム鉱石を層状に積層した状態で反応容器２に装入し、又はシリコクロムを反応容器２に装入した後、追装クロム鉱石を反応容器２に装入するので、追装クロム鉱石の溶解に還元反応の反応熱を有効に利用できる。
　（実施例１） The reaction chrome ore is charged into the reaction vessel 2 in a state where silicochrome and the additional chrome ore are mixed or in a state where the silicochrome and the additional chrome ore are laminated in layers, or after the silicochrome is charged in the reaction vessel 2, the additional chrome ore is added. Since it is charged into the reaction vessel 2, the reaction heat of the reduction reaction can be effectively used for dissolving the chasing chromium ore.
(Example 1)
　図１の製造工程図に従って低炭素フェロクロムを製造した。表２には、本実施例で使用した原料であるクロム鉱石の組成を示す。
Figure JPOXMLDOC01-appb-T000002
 Low carbon ferrochrome was produced according to the production process diagram of FIG. Table 2 shows the composition of the chromium ore as the raw material used in this example.
Figure JPOXMLDOC01-appb-T000002
　クロム鉱石１０００ｋｇ、生石灰８３０ｋｇを固定型電気炉に装入し、溶解させて１次スラグを溶製した。１次スラグを反応容器に出湯し、その中に追装クロム鉱石７５０ｋｇと、副原料シリコクロム３１０ｋｇと、回収シリコクロム２６０ｋｇを装入した。次いで、反応容器２にアルゴンガスを底吹きして攪拌した。反応容器２の溶湯の反応終点温度は１６５０℃であった。そして、生成した２次スラグを分離し、得られた低炭素フェロクロム１０００ｋｇの溶湯を鋳型に鋳込んで製品にした。表３には、製品である低炭素フェロクロムの組成を示す。フェロクロムの各成分の定量化方法は、「ＪＩＳ　Ｇ１３０１－１～５　２０１２」に規格化されている。 1000 kg of chrome ore and 830 kg of quicklime were charged into a fixed electric furnace and melted to melt the primary slag. The primary slag was discharged into a reaction vessel, and 750 kg of additional chromium ore, 310 kg of auxiliary raw material siliconochrome, and 260 kg of recovered siliconochrome were charged therein. Next, argon gas was bottom-blown into the reaction vessel 2 and stirred. The reaction end temperature of the molten metal in the reaction vessel 2 was 1650 ° C. Then, the produced secondary slag was separated, and the obtained molten metal of 1000 kg of low-carbon ferrochrome was cast into a mold to obtain a product. Table 3 shows the composition of the product, low carbon ferrochrome. The method for quantifying each component of ferrochrome is standardized in "JIS G1301-1 to 5 2012".
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　一方、分離した２次スラグを反応容器に受け、フェロシリコン２３０ｋｇを装入し、反応容器にアルゴンガスを底吹きして攪拌した。次いで、生成した３次スラグと回収シリコクロムを分離し、３次スラグ１９３０ｋｇと回収シリコクロム２６０ｋｇを得た。この回収シリコクロムは副原料シリコクロムと共に１次スラグに装入した。表４には、３次スラグの組成を示し、表５には、回収シリコクロムの組成を示す。 On the other hand, the separated secondary slag was received in a reaction vessel, 230 kg of ferrosilicon was charged, and argon gas was bottom-blown into the reaction vessel to stir. Then, the produced tertiary slag and recovered silicochrome were separated to obtain 1930 kg of tertiary slag and 260 kg of recovered silicochrome. This recovered silicochrome was charged into the primary slag together with the auxiliary raw material silicochrome. Table 4 shows the composition of the tertiary slag, and Table 5 shows the composition of the recovered silicochrome.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000005
 　電力原単位は、２２００ｋｗｈ／ｔという低い値が得られた。電力原単位は、製品ｔ当たりに使用された電力量であり、具体的には（１次スラグ溶解電力量／製品生産量）である。
　（実施例２）
Figure JPOXMLDOC01-appb-T000005
 A low value of 2200 kwh / t was obtained for the power intensity. The electric power intensity is the amount of electric power used per product t, and specifically (primary slag dissolved electric energy / product production amount).
(Example 2)
　図１の製造工程図に従って低炭素フェロクロムを製造した。表６に示すように、操業１では追装率を１３％に設定し、操業２では追装率を２１％に設定し、操業３では追装率を４０％に設定し、操業４では追装率を６５％に設定した。表６に示すように、追装率を１３％～６５％に上げても、３次スラグの塩基度は１．０であり、３次スラグに有害な６価クロムが発生するのを抑制できた。電力原単位は、２４００Ｋｗｈ／ｔ以下という低い値であり、追装率を上げれば上げるほど、電力原単位を低減できた。
Figure JPOXMLDOC01-appb-T000006
 　（従来例） Low carbon ferrochrome was produced according to the production process diagram of FIG. As shown in Table 6, the follow-up rate is set to 13% in operation 1, the follow-up rate is set to 21% in operation 2, the follow-up rate is set to 40% in operation 3, and the follow-up rate is set in operation 4. The dressing rate was set to 65%. As shown in Table 6, even if the tracking rate is increased from 13% to 65%, the basicity of the tertiary slag is 1.0, and the generation of hexavalent chromium harmful to the tertiary slag can be suppressed. It was. The power intensity was as low as 2400 Kwh / t or less, and the higher the tracking rate, the more the power intensity could be reduced.
Figure JPOXMLDOC01-appb-T000006
 (Conventional example)
　図７の製造工程図に従って低炭素フェロクロムを製造した。この低炭素フェロクロムの製造工程においては、１次スラグの還元操作をリレードリングによって行う点、１次スラグに追装クロム鉱石を装入していない点、２次スラグから回収シリコクロムを回収し、これを１次スラグに添加する操作を行っていない点が本実施例と相違する。表７には、従来例で使用した原料であるクロム鉱石の組成を示す。 Low carbon ferrochrome was produced according to the production process diagram of FIG. In the manufacturing process of this low carbon ferrochrome, the reduction operation of the primary slag is performed by relaying, the primary slag is not charged with additional chromium ore, and the recovered siliconochrome is recovered from the secondary slag. Is different from this embodiment in that the operation of adding the slag to the primary slag is not performed. Table 7 shows the composition of the chromium ore which is the raw material used in the conventional example.
Figure JPOXMLDOC01-appb-T000007
Figure JPOXMLDOC01-appb-T000007
　クロム鉱石１７４０ｋｇ、生石灰１０６０ｋｇを電気炉に装入し、溶解させて１次スラグを溶製した。１次スラグを取鍋に出湯し、追装クロム鉱石を装入せずに副原料シリコクロム６００ｋｇを装入した。次いで、リレードリングにより攪拌した。そして、生成した２次スラグ２２００ｋｇを分離し、得られた低炭素フェロクロム１０００ｋｇの溶湯を鋳型に鋳込んで製品にした。表８には、製品である低炭素フェロクロムの組成を示し、表９には、２次スラグの組成を示す。 1740 kg of chrome ore and 1060 kg of quicklime were charged into an electric furnace and melted to melt the primary slag. The primary slag was poured into a ladle, and 600 kg of the auxiliary raw material silicochrome was charged without charging the additional chromium ore. Then, the mixture was stirred by relaying. Then, 2200 kg of the produced secondary slag was separated, and 1000 kg of the obtained molten metal of low carbon ferrochrome was cast into a mold to obtain a product. Table 8 shows the composition of the product low carbon ferrochrome, and Table 9 shows the composition of the secondary slag.
Figure JPOXMLDOC01-appb-T000008
Figure JPOXMLDOC01-appb-T000008
Figure JPOXMLDOC01-appb-T000009
 　電力原単位は、２９８０ｋｗｈ／ｔという高い値であった。
Figure JPOXMLDOC01-appb-T000009
 The power intensity was as high as 2980 kwh / t.
　本明細書は、２０１９年７月１２日出願の特願２０１９－１３０３２２に基づく。この内容はすべてここに含めておく。 This specification is based on Japanese Patent Application No. 2019-130322 filed on July 12, 2019. All this content is included here.
　Ｓ１…第１工程
　Ｓ２…第２工程
　２…反応容器
　２ａ…ガス底吹き装置
　１１…プラグの本体
　１５…スリット
　１９…プラグ S1 ... 1st process S2 ... 2nd process 2 ... Reaction vessel 2a ... Gas bottom blowing device 11 ... Plug body 15 ... Slit 19 ... Plug

Claims (8)

  1. 　クロム鉱石と生石灰を電気炉で溶解する第１工程と、
    　ガス底吹き装置を有する反応容器に前記第１工程で溶解した溶解原料（以下、１次スラグという）を出湯し、還元剤と前記１次スラグに対して質量比で１０％以上１００％以下の追装クロム鉱石を含有する冷材を装入し、前記ガス底吹き装置から不活性ガスを底吹きすることにより撹拌して、低炭素フェロクロムと２次スラグを生成させる第２工程と、を備える低炭素フェロクロムの製造方法。     The first step of melting chrome ore and quicklime in an electric furnace,
    The dissolved raw material (hereinafter referred to as primary slag) dissolved in the first step is discharged into a reaction vessel having a gas bottom blowing device, and the mass ratio of the reducing agent and the primary slag is 10% or more and 100% or less. It is provided with a second step of charging a cold material containing a follow-up chrome ore and stirring by bottom blowing an inert gas from the gas bottom blowing device to generate low carbon ferrochrome and secondary slag. A method for producing low carbon ferrochrome.
  2. 　前記ガス底吹き装置の攪拌ガス量が、溶湯１ｔ当たり５ｌ／ｍｉｎ以上１０００ｌ／ｍｉｎ以下であることを特徴とする請求項１に記載の低炭素フェロクロムの製造方法。 The method for producing low-carbon ferrochrome according to claim 1, wherein the amount of agitated gas in the gas bottom blowing device is 5 l / min or more and 1000 l / min or less per 1 ton of the molten metal.
  3. 　前記２次スラグの酸化クロム含有率（Ｃｒ２Ｏ３質量％）を１０．０質量％以下、塩基度（ＣａＯ／ＳｉＯ２）を１．６５未満に調整することを特徴とする請求項１又は２に記載の低炭素フェロクロムの製造方法。 Claim 1 or claim 1, wherein the chromium oxide content (Cr 2 O 3 % by mass) of the secondary slag is adjusted to 10.0% by mass or less, and the basicity (CaO / SiO 2 ) is adjusted to less than 1.65. 2. The method for producing low carbon ferrochrome according to 2.
  4. 　前記反応容器の低炭素フェロクロムと前記２次スラグの溶湯の反応終点温度が１３５０℃以上１９００℃以下であることを特徴とする請求項１ないし３のいずれか一項に記載の低炭素フェロクロムの製造方法。 The production of low-carbon ferrochrome according to any one of claims 1 to 3, wherein the reaction end point temperature of the low-carbon ferrochrome in the reaction vessel and the molten metal of the secondary slag is 1350 ° C. or higher and 1900 ° C. or lower. Method.
  5. 　前記反応容器の底部の中央部に前記ガス底吹き装置の不活性ガスを吹き出す１つのプラグを配置し、及び／又は前記反応容器の底部の中央部を中心にした円上に前記ガス底吹き装置の不活性ガスを吹き出す複数のプラグを配置することを特徴とする請求項１ないし４のいずれか一項に記載の低炭素フェロクロムの製造方法。 One plug for blowing out the inert gas of the gas bottom blowing device is arranged at the center of the bottom of the reaction vessel, and / or the gas bottom blowing device is placed on a circle centered on the center of the bottom of the reaction vessel. The method for producing a low carbon ferrochrome according to any one of claims 1 to 4, wherein a plurality of plugs for blowing out the inert gas of the above are arranged.
  6. 　前記ガス底吹き装置は、不活性ガスを吹き出す複数のスリットを有するスリット式プラグを備えることを特徴とする請求項１ないし５のいずれか一項に記載の低炭素フェロクロムの製造方法。 The method for producing low-carbon ferrochrome according to any one of claims 1 to 5, wherein the gas bottom blowing device includes a slit type plug having a plurality of slits for blowing out the inert gas.
  7. 　前記スリット式プラグがＭｇＯ及び／又はＡｌ２Ｏ３を含む耐火物からなる本体を備え、
    　前記耐火物からなる前記本体に前記複数のスリットを形成することを特徴とする請求項６に記載の低炭素フェロクロムの製造方法。     The slit type plug includes a main body made of a refractory material containing MgO and / or Al 2 O 3 .
    The method for producing a low-carbon ferrochrome according to claim 6, wherein the plurality of slits are formed in the main body made of the refractory material.
  8. 　前記還元剤と前記追装クロム鉱石を混合した状態で若しくは前記還元剤と前記追装クロム鉱石を層状に積層した状態で前記反応容器に装入し、又は前記還元剤を前記反応容器に装入した後、前記追装クロム鉱石を前記反応容器に装入することを特徴とする請求項１ないし７のいずれか一項に記載の低炭素フェロクロムの製造方法。 The reducing agent and the additional chromium ore are mixed, or the reducing agent and the additional chromium ore are laminated in a layered state, and the reaction vessel is charged, or the reducing agent is charged into the reaction vessel. The method for producing low carbon ferrochrome according to any one of claims 1 to 7, wherein the additional chromium ore is charged into the reaction vessel.
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JP2003049235A (en) * 2000-03-07 2003-02-21 Nkk Corp Chromium-containing metal and production method therefor
JP2011094210A (en) * 2009-10-30 2011-05-12 Jfe Material Co Ltd Decarbonizing method for silicochromium
JP2012041618A (en) * 2010-08-23 2012-03-01 Shinagawa Refractories Co Ltd Gas blowing plug and production method thereof
JP2013142189A (en) * 2012-01-12 2013-07-22 Nippon Steel & Sumitomo Metal Corp Method for reducing spitting in decarburize-refining in converter
JP2015137369A (en) * 2014-01-20 2015-07-30 新日鐵住金株式会社 Bottom blowing agitation method for steel making arc furnace and arc furnace for steel making by bottom blowing agitation
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JP2003049235A (en) * 2000-03-07 2003-02-21 Nkk Corp Chromium-containing metal and production method therefor
JP2011094210A (en) * 2009-10-30 2011-05-12 Jfe Material Co Ltd Decarbonizing method for silicochromium
JP2012041618A (en) * 2010-08-23 2012-03-01 Shinagawa Refractories Co Ltd Gas blowing plug and production method thereof
JP2013142189A (en) * 2012-01-12 2013-07-22 Nippon Steel & Sumitomo Metal Corp Method for reducing spitting in decarburize-refining in converter
JP2015137369A (en) * 2014-01-20 2015-07-30 新日鐵住金株式会社 Bottom blowing agitation method for steel making arc furnace and arc furnace for steel making by bottom blowing agitation
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