JP7780899B2 - Carbon recovery type manganese alloy manufacturing method and manufacturing device - Google Patents

Description

The present invention relates to a method and apparatus for producing manganese alloys with carbon recovery, in which carbon monoxide contained in by-product gases generated during the production of manganese alloys is used as a raw material to produce synthetic fuel and recover the carbon.

Manganese-based alloys, such as ferromanganese, are produced by heating manganese ore and a reducing agent such as coke in a blast furnace or electric furnace to reduce the manganese and iron in the ore. While the blast furnace method uses coke as both the heat source and the reducing agent, the basic concept of the electric furnace method is that electricity is used as the heat source and coke as the reducing agent.

Traditionally, technological development in the production of manganese-based alloys has focused on how to produce them as efficiently as possible. For example, Patent Documents 1 and 2 disclose technologies that add reducing agents such as silicon-containing ferroalloys or metallic aluminum to further reduce and extract the manganese remaining in the slag. Furthermore, Patent Documents 3 to 6 disclose technologies that, rather than directly adding manganese ore to a blast furnace or electric furnace, pre-reduce manganese ore with carbon monoxide (CO) gas or coke generated in the blast furnace or electric furnace process before adding it to the blast furnace or electric furnace.

Japanese Patent Application Laid-Open No. 2006-161079 Japanese Unexamined Patent Publication No. 59-222552 Japanese Unexamined Patent Publication No. 63-195244 Japanese Patent Application Publication No. 59-215458 Special Publication No. 38-4456 Special Publication No. 38-12811

As mentioned above, technological developments have been made to efficiently produce manganese alloys, but the by-product gases that are generated have only been used for the pre-reduction of ore or as fuel for power generation, as mentioned above.

However, Patent Documents 1 to 5 and other prior art documents related to the production of manganese-based alloys do not describe or suggest any technological development aimed at reducing _CO2 emissions. Conventional technological developments related to the production of manganese-based alloys have indirectly reduced _CO2 emissions to some extent by increasing efficiency, but no efforts have been made to recover carbon from the by-product gases generated from the perspective of reducing _CO2 emissions.

We came to the conclusion that it is necessary to develop technology for manufacturing manganese-based alloys that are carbon neutral and have _{zero CO2} emissions in order to address the issue of global warming.

The present invention has been made in consideration of the above problems, and aims to provide a carbon recovery type manganese-based alloy production method and production apparatus that enable a reduction in _CO2 emissions in the production of manganese-based alloys.

The by-product gases generated in the production of manganese alloys using conventional electric furnace methods contain 45% to 65% carbon monoxide (CO), and as mentioned above, are used as fuel for the preliminary reduction of manganese ore and for power generation. However, the use of these by-product gases does not fix or capture carbon, and instead the carbon is emitted as carbon dioxide (CO2 ₎ .

The inventors came up with the idea of recovering carbon by using the CO contained in by-product gas as a raw material to produce synthetic fuel. However, while current by-product gas contains CO, the content is at most 65%, and an even higher concentration of CO is required to efficiently produce synthetic fuel. Therefore, the inventors conducted further research and, by considering the mechanism of CO generation in exhaust gas during the production of manganese-based alloys, discovered a method to produce exhaust gas (by-product gas) containing a high concentration of CO, preferably 80% or more. Specifically, they discovered that when manganese-based alloys are produced using manganese ore-derived raw materials with a manganese oxidation degree of 1.0 to 1.1, the exhaust gas contains a high concentration of CO, leading to the completion of this invention.

(1) A method for producing a carbon-recovery manganese alloy, comprising the steps of: (A) feeding a manganese ore-derived raw material having a manganese oxidation degree of 1.0 to 1.1 and a carbonaceous material into an electric furnace for refining, followed by slag-metal separation; and (B) producing a synthetic fuel using carbon monoxide contained in the by-product gas generated from the electric furnace as a raw material.

(2) The method for producing a carbon-recovery manganese-based alloy according to (1), wherein the manganese ore-derived raw material is obtained by reducing manganese ore with hydrogen or carbon monoxide, or with both hydrogen and carbon monoxide, to a manganese oxidation degree of 1.0 to 1.1.

(3) A method for producing a carbon-recovery manganese alloy according to (1) or (2), wherein some or all of the carbon monoxide is carbon monoxide contained in a by-product gas generated from an electric furnace.

(4) A method for producing a carbon-recovery manganese-based alloy according to any one of (1) to (3), wherein some or all of the carbonaceous material is green carbon.

(5) A method for producing a carbon-recovery manganese alloy according to any one of (1) to (4), characterized in that granules containing the manganese ore-derived raw material and carbonaceous material are charged into the electric furnace.

(6) A method for producing a manganese-based alloy with carbon recovery according to any one of (1) to (5), characterized by including step (C) of adding a reducing agent containing a silicon-containing ferroalloy or metallic aluminum, or both a silicon-containing ferroalloy and a reducing agent containing metallic aluminum, to the molten slag by-produced in step (A) to reduce at least a portion of the manganese oxide contained in the molten slag to produce a manganese-based ferroalloy.

(7) A carbon-recovery manganese alloy manufacturing apparatus characterized by combining a means (A) for feeding manganese ore-derived raw material with a manganese oxidation degree of 1.0 to 1.1 and carbonaceous material into an electric furnace for refining, followed by slag-metal separation, and a means (B) for producing synthetic fuel using carbon monoxide contained in the by-product gas generated from the electric furnace as a raw material.

(8) The carbon recovery type manganese alloy manufacturing apparatus according to (9), wherein the manganese ore-derived raw material is obtained by reducing manganese ore with hydrogen or carbon monoxide, or with both hydrogen and carbon monoxide, to a manganese oxidation degree of 1.0 to 1.1.

(9) The carbon recovery type manganese alloy manufacturing apparatus according to (7) or (8), wherein some or all of the carbon monoxide is carbon monoxide contained in a by-product gas generated from an electric furnace.

(10) A carbon recovery type manganese alloy manufacturing apparatus according to any one of (7) to (9), characterized in that some or all of the carbonaceous material is green carbon.

(11) The carbon recovery type manganese alloy manufacturing apparatus according to any one of (7) to (10), characterized in that granulated material containing the manganese ore-derived raw material and carbonaceous material is fed into the electric furnace.

(12) A carbon-recovery manganese alloy manufacturing apparatus according to any one of (7) to (11), characterized by including a step (C) of adding a reducing agent containing a silicon-containing ferroalloy or metallic aluminum, or both a silicon-containing ferroalloy and a reducing agent containing metallic aluminum, to the molten slag by-produced in the step (A) to reduce at least a portion of the manganese oxide contained in the molten slag to produce a manganese-containing ferroalloy.

This invention has the effect of increasing the carbon monoxide (CO) concentration in the by-product gas during the production of manganese-based alloys, thereby enabling the efficient production of synthetic fuels. It also has the effect of recovering carbon emitted during the production of manganese-based alloys.

Temperature dependence of Gibbs free energy ΔG (chemical potential) of each reaction Example of thermogravimetric analysis results of manganese ore (comilog) in a 4% hydrogen/nitrogen mixed gas One example of a production flow of a carbon recovery type manganese alloy according to an embodiment of the present invention Another example of the manufacturing flow of a carbon recovery type manganese alloy according to an embodiment of the present invention Example of a conventional manganese alloy manufacturing flow

In conventional electric furnace manufacturing of manganese-based alloys, coke is used as a carbonaceous material to reduce the manganese and iron in manganese ore. The inventors have discovered that the coke added to an electric furnace can be used primarily in the following reactions:

MnO ₂ (manganese ore) + CO → MnO + CO ₂ (Equation 1)
MnO + C (coke) → Mn + CO (Equation 2)
MnO ₂ + C → Mn + CO ₂ ...(Formula 1) + (Formula 2)...(Formula 3)
1/2Fe ₂ O ₃ + 3/4C → Fe + 3/4CO ₂ ... (Formula 4)
C + CO ₂ → 2CO (Formula 5)
The coke introduced reduces manganese ore (containing iron oxide) to a manganese-based alloy (e.g., ferromanganese), and then turns into carbon dioxide _CO2 , which is then discharged from the electric furnace. However, in reality, the coke is introduced for the next reaction, and the carbon dioxide _CO2 and the coke C undergo a solution-loss reaction (Boudouard reaction), resulting in the coke being consumed for purposes other than the reduction of the manganese ore. Therefore, while the by-product gas produced in the conventional electric furnace process theoretically contains carbon dioxide _CO2 , in reality, it also contains carbon monoxide CO, which is produced by the solution-loss reaction. Therefore, the inventors came up with the idea that the concentration of carbon monoxide CO contained in the by-product gas is determined by equilibrium theory and kinetics, and is therefore limited to a maximum of approximately 65%.

The present inventors have further investigated the reduction reaction of manganese ore in detail and found that tetravalent manganese (equivalent to _MnO2 ) can be reduced to divalent manganese (equivalent to MnO) using carbon monoxide (CO), but divalent manganese (equivalent to MnO) cannot be reduced to zerovalent manganese (metallic Mn) using carbon monoxide (CO) and can only be reduced by carbon (C) (Figure 1). Based on this, the present inventors have arrived at the following invention.

That is, when a manganese alloy (ferromanganese) is produced in an electric furnace using reduced manganese ore in which the manganese ions in the manganese ore have been reduced in advance, preferably to divalent manganese (MnO), the carbonaceous material introduced into the electric furnace is reduced to metallic manganese (ferromanganese) according to the reaction of (Equation 2) and carbon monoxide (CO) is generated. That is, since the reaction of (Equation 1) does not occur in an electric furnace, the gas generated is mainly carbon monoxide (CO) generated by the reaction of (Equation 2). Therefore, carbon dioxide (CO2 ₎ is not generated as in conventional electric furnaces, and the solution loss reaction of (Equation 5) does not occur. That is, the gas discharged from the electric furnace is mostly carbon monoxide (CO), with nearly no carbon dioxide ( _CO2) .

By operating the electric furnace in the manner described above, the carbon monoxide (CO) contained in the by-product gas generated can be increased in concentration, allowing synthetic fuel to be produced efficiently using the by-product gas. Furthermore, efficient synthetic fuel production also means efficient carbon recovery. According to one embodiment, the carbon monoxide (CO) concentration contained in the by-product gas is 80% or more, 84% or more, 87% or more, or 90% or more. In reality, it is 99% or less, or 98% or less.

Therefore, the method for producing a carbon-recovery manganese alloy of the present invention combines process (A) of refining a manganese ore-derived raw material with a manganese oxidation degree of 1.0 to 1.1 and a carbonaceous material in an electric furnace, followed by slag/metal separation, with process (B) of producing a synthetic fuel using carbon monoxide contained in the by-product gas generated from the electric furnace as a raw material.

In the present invention, the manganese ore-derived raw material may be prepared by any method as long as it has a manganese oxidation degree in the range of 1.0 to 1.1. For example, the manganese ore-derived raw material is prepared by reducing manganese ore, and examples of the reducing agent include coal, coke, hydrocarbons (LNG, LPG, etc.), hydrogen, and carbon monoxide. Among these, the manganese ore-derived raw material is preferably prepared by reducing manganese ore with hydrogen or carbon monoxide, or with both hydrogen and carbon monoxide, to a manganese oxidation degree of 1.0 to 1.1. When the manganese ore-derived raw material is prepared by reduction with these materials, _CO2 emissions can be reduced. From the viewpoint of reducing _CO2 emissions, it is more preferable to prepare the manganese ore-derived raw material using hydrogen.

Furthermore, when the manganese ore-derived raw material is produced using carbon monoxide (CO), it is preferable that some or all of the carbon monoxide be carbon monoxide contained in the by-product gas generated from the electric furnace. This will increase energy efficiency.

Therefore, it is more preferable to include a step of producing the manganese ore-derived raw material from manganese ore.

Here, the manganese oxidation degree (Mn oxidation degree) will be explained. When expressed as the composition formula MnOx, the value of x is the manganese oxidation degree; for example, a manganese oxidation degree of x=2 is _MnO2 , and a manganese oxidation degree of x=1 is MnO. Therefore, the manganese oxidation degree of manganese ore or reduced manganese ore is determined by finding x of MnOx from the total manganese amount (Mn%, JIS M8232 Manganese ore - Manganese determination method) and the available oxygen value of manganese oxide ( _MnO2 %, JIS M8233 Manganese ore - Active oxygen determination method), and this is taken as the manganese oxidation degree.

The manganese oxidation degree of the manganese ore-derived raw material is 1.0 to 1.1. Ideally, a manganese oxidation degree of 1.0 is most preferable, but in reality, the effects of the present invention can be sufficiently obtained even with a manganese oxidation degree of 1.1 or less. If the manganese oxidation degree exceeds 1.1, the carbon monoxide (CO) content in the by-product gas becomes too low and the carbon dioxide (CO2 ₎ content becomes too high, resulting in inefficient production of synthetic fuel from the by-product gas. A more preferable range of the manganese oxidation degree is 1.0 to 1.05.

Regarding the hydrogen reduction of manganese ore to produce a manganese ore-derived raw material, any conditions containing hydrogen are acceptable, and more preferably, the proportion of hydrogen in the reducing agent is 50% or more, even more preferably 70% or more, even more preferably more than 70%, and even more preferably 90% or more. Most preferably, no reducing agent that generates _CO2 is included, or the reducing agent contains only impurity levels.

In addition to the reducing agent, the mixture may contain nitrogen, water vapor, CO ₂ , argon, helium, oxygen, nitrogen oxides, etc. The hydrogen content in the hydrogen reduction is sufficient as long as it can reduce the manganese ore to the desired oxidation level, but it may also be, for example, 1% or more and 10% or less, or 5% or less, or 4% or less.

The heating required to reduce manganese ore to produce a manganese ore-derived raw material may be any heating method capable of heating the manganese ore to a temperature at which the manganese ore can be reduced. However, a heating method capable of reducing carbon dioxide (CO2 ₎ emissions is preferred. For example, electric heating is preferred from the viewpoint of reducing carbon dioxide (CO2 ₎ emissions. Furthermore, heating by hydrogen combustion is preferred from the viewpoint of reducing carbon dioxide (CO2 ₎ emissions and being able to be performed simultaneously with hydrogen supply. The heating may be performed to a temperature at which the manganese ore can be reduced. For example, reduction can be performed at a temperature of 750°C or higher and 1250°C or lower. The higher the temperature, the faster the reduction. However, at temperatures exceeding 1250°C, the manganese ore may solidify due to sintering or partial melting, making it difficult to handle. On the other hand, at temperatures below 750°C, reduction may be insufficient or take too long. A more preferred temperature is 800°C or higher and 1200°C or lower. In this case, the temperature may be higher than 1000°C, 1050°C or higher, or 1080°C or higher, and in this case, there is an effect that reduction can be carried out in a short time without causing partial melting.

Furthermore, iron oxide (e.g., _Fe2O3 ) contained in small amounts in manganese ore is preferably reduced to metallic iron ₍ Fe) when used as the manganese ore-derived raw material. This is because iron oxide can also be reduced by carbon monoxide (CO) to metallic iron, producing carbon dioxide (CO2 ₎ , which increases the proportion of carbon dioxide contained in the by-product gas, albeit slightly. Furthermore, a solution loss reaction between carbon dioxide (CO2 ₎ and the carbonaceous material occurs in the electric furnace, reducing the utilization rate of the carbonaceous material. In other words, an increased amount of carbonaceous material is required to compensate for the amount consumed in the reaction, albeit slightly.

The manganese ore-derived raw material prepared by the above method is placed in an electric furnace together with carbonaceous material for refining, followed by separation of slag and metal to produce a manganese-based alloy. The electric furnace may be a conventional submerged arc furnace or an equivalent. It is heated primarily by electricity and is used primarily by carbonaceous material to reduce the manganese ore-derived raw material to metallic manganese (manganese-based alloy). As refining progresses in the electric furnace, molten slag and molten manganese-based alloy are formed. Due to the difference in their specific gravities, the molten manganese-based alloy is positioned at the bottom of the furnace and the molten slag is positioned above it. Depending on the timing of the tapping and the height of the tapping opening, the slag and metal are separated and discharged from the electric furnace. Manganese-based alloys produced using carbonaceous material in this way yield carbon-containing ferromanganese, which may then be decarburized depending on the intended use.

According to one embodiment, the electric furnace is operated so that the slag produced contains approximately 30% manganese by mass. A process may be added in which some or all of the slag is refined by molten oxide electrolysis, followed by slag-metal separation. Molten oxide electrolysis involves melting reduced manganese ore, placing two electrodes (an anode and a cathode) in contact with the molten material, and applying a voltage sufficient to reduce divalent manganese to zerovalent manganese (metallic manganese), thereby producing molten metallic manganese (manganese-based alloy). The heat source for melting the reduced manganese ore can be electric heating, utilizing Joule heat generated by the current flowing between the electrodes, or a separate heat source can be used. Manganese-based alloys produced in this way without using carbonaceous materials result in ferromanganese or metallic manganese that contains almost no carbon.

Furthermore, if the process includes a step of producing a manganese-based ferroalloy by adding a reducing agent containing a silicon-containing ferroalloy or metallic aluminum, or both a silicon-containing ferroalloy and metallic aluminum, to the slag obtained in the electric furnace to reduce at least a portion of the manganese oxide contained in the molten slag, the manganese remaining in the slag can be recovered, thereby improving productivity. In this way, manganese-based alloys produced from Mn-containing slag without using carbonaceous materials can produce ferromanganese or metallic manganese that contains almost no carbon.

The carbonaceous material used in the electric furnace in step (A) may be conventional coke, but using green carbon in part or in whole can further improve the carbon dioxide (CO2 ₎ reduction effect. Examples of green carbon include biocarbon (biologically derived carbonaceous materials such as charcoal and bamboo charcoal), coke made from waste plastics, fuel-derived carbonaceous materials obtained from hydrogen and carbon dioxide synthesized using renewable energy, and green coke synthesized using renewable energy. In particular, when biocarbon (biocoke) obtained by fixing carbon dioxide is used in an electric furnace and synthetic fuel is produced from by-product gas, the process not only does not emit carbon dioxide (carbon neutral) but also fixes carbon dioxide (carbon negative).

In addition, some or all of the carbonaceous material may be granulated together with manganese ore-derived raw materials and charged into an electric furnace as carbonaceous material-containing pellets. By forming such carbonaceous material-containing pellets, the reduction reaction and gas release within the electric furnace may be improved, making operation more stable and improving the carbonaceous material consumption rate.

Furthermore, crushed manganese alloy product chips or raw manganese ore fines may be included in the carbonaceous composite pellets. The above-mentioned carbonaceous composite pellets are more effective when green carbon is used, and using green carbon as the carbonaceous material in the carbonaceous composite pellets allows the green carbon to act more efficiently as a reducing agent.

Conventional methods can be used to produce carbonaceous composite pellets, such as pelleting, briquetting, and extrusion molding. Therefore, it is more preferable to include a step of granulating manganese ore-derived raw material, carbonaceous material, and optionally adding binders and crushed product debris, to produce carbonaceous composite pellets.

A slag former (slag adjuster) can be added to the electric furnace in step (A) to control the viscosity, oxygen potential, basicity, and other properties of the slag, and examples of such slag formers include lime, slaked _lime , _Na2CO3 , _CaCl2 , and _MgCO2 .

In step (B) of producing a synthetic fuel using carbon monoxide contained in the by-product gas generated from the electric furnace as a raw material, any method may be used as long as it can produce a synthetic fuel. The synthetic fuel in the present invention is a hydrocarbon synthesized from carbon monoxide. Examples of such methods include synthesis using hydrogen (H2 ₎ and various catalysts. Examples include the production of methane using a nickel (Ni)-based catalyst, the production of methanol using a copper (Cu)-based catalyst (Cu/ZnO, Cu/ _ZrO2 ), the production of dimethyl ether (DME) by dehydration of methanol, and the production of gasoline or diesel fuel by Fischer-Tropsch (FT) synthesis. Catalysts are also used in FT synthesis, including Co, Fe, and Ru-based catalysts.

Any type of hydrogen (H2 ₎ can be used for the synthetic fuel, but from the perspective of reducing _CO2 emissions, blue hydrogen or turquoise hydrogen is preferable to gray hydrogen, and green hydrogen is preferable to blue hydrogen or turquoise hydrogen. Other types of hydrogen that can be used include yellow hydrogen, brown hydrogen, and white hydrogen. Here, gray hydrogen is hydrogen produced from fossil fuels (for example, by reacting natural gas with steam to produce hydrogen ( _H2) and carbon dioxide ( _CO2 )).

Like gray hydrogen, blue hydrogen is hydrogen produced from fossil fuels, but _CO2 emissions are reduced to zero by capturing and geologically storing the carbon dioxide produced. Turquoise hydrogen is hydrogen ( _{H2 )} produced by the thermal decomposition of methane (CH4 ₎ . The carbon (C) contained in methane is fixed as solid carbon (C) in carbon nanotubes and other materials. The high-temperature reactors used to produce turquoise hydrogen use renewable energy. Yellow hydrogen is produced by electrolyzing water ( _H2O ) using nuclear power to produce hydrogen (H2 ₎ and oxygen ( _{O2 )} . This method produces zero _CO2 emissions but generates nuclear waste. Brown hydrogen is hydrogen ( _H2) produced from coal. It is also gray hydrogen, but emits more _CO2 than gray hydrogen. White hydrogen is hydrogen ( _H2) produced as a by-product in the production of other products (such as steelmaking). Therefore, production volume cannot be controlled. Green hydrogen is hydrogen (H2 ₎ synthesized using renewable energy-derived electricity by electrolyzing water ( _H2O ) into hydrogen ( _H2) and oxygen (O2 ₎ with zero carbon dioxide (CO2 ₎ emissions.

It is more preferable to include a desulfurization process, a dechlorination process, or both of these processes for the by-product gas prior to the process for producing the synthetic fuel.

The manganese-based alloy manufacturing apparatus that achieves the above-described method for producing manganese-based alloys includes a means (A) for feeding manganese ore-derived raw materials with a manganese oxidation degree of 1.0 to 1.1 and carbonaceous material into an electric furnace for refining, followed by slag/metal separation, and a means (B) for producing synthetic fuel using carbon monoxide contained in the by-product gas generated from the electric furnace as a raw material.

It is more preferable that the method further comprises a means (C) for producing a manganese-based ferroalloy by adding a reducing agent containing a silicon-containing ferroalloy or metallic aluminum, or both a silicon-containing ferroalloy and a reducing agent containing metallic aluminum, to the molten slag by-produced in the means (A) to reduce at least a portion of the manganese oxide contained in the molten slag.
It is more preferable that the apparatus further includes a means (D) for reducing manganese ore to produce a manganese ore-derived raw material having a manganese oxidation degree of 1.0 to 1.1, and a granulating means (E) for producing carbonaceous material-containing pellets containing the manganese ore-derived raw material and a carbonaceous material.

The following is an example of the present invention.

(Production of manganese ore-derived raw materials)
This example shows the production of manganese ore-derived raw material with a manganese oxidation degree of 1.0 to 1.1 by heating and hydrogen-reducing manganese ore such as manganese ore from Gabon (Comilog) and manganese ore from South Africa (Assoman).

Industrial furnaces capable of heating and reducing manganese ore, such as fluidized bed furnaces, shaft furnaces, and rotary kilns, were used. Experimentally, manganese ore was heated in a tubular furnace and reduced with hydrogen gas to produce reduced manganese ore. As an example, Gabonese manganese ore (containing _MnO2 ) was placed in an alumina boat and charged into a tubular furnace. It was then heated at 1100°C for 5 hours while flowing 4% hydrogen/nitrogen gas, yielding a manganese ore-derived raw material. The manganese oxidation degree of the resulting manganese ore-derived raw material was measured and calculated according to the above-mentioned measurement methods (JIS M8232 and JIS M8233), resulting in a manganese oxidation degree of 1.05. Similar results were obtained using South African manganese ore (Assoman). A similar test was also performed using 10% carbon monoxide/nitrogen gas instead of hydrogen gas, yielding a manganese ore-derived raw material. The manganese oxidation degree was 1.05. Furthermore, when manganese ore is mixed with 8% by mass of coke and subjected to a similar test using nitrogen gas, a manganese ore-derived raw material is obtained. The manganese oxidation degree is 1.0.

Furthermore, when thermogravimetric analysis was performed on the manganese ore while flowing a 4% hydrogen/nitrogen mixed gas, a mass loss due to manganese reduction was confirmed, as shown in Figure 2. It was found that hydrogen reduction was possible when the ore was heated to 750°C or higher. Increasing the hydrogen reduction temperature makes it easier to reduce manganese ore, shortening the reduction process time, for example. However, if the hydrogen reduction temperature is too high, the reduced manganese ore may stick together (sintering or fusion solidification) and solidify, making it difficult to handle. For these reasons, the hydrogen reduction temperature is preferably 1250°C or lower, and more preferably 1200°C or lower. As mentioned above, a hydrogen concentration of 4% is sufficient for hydrogen reduction, but it may be increased to 4% or higher for more efficient reduction. Conversely, a hydrogen concentration of around 1% is sufficient for reduction, but because hydrogen-containing gas is supplied in accordance with the amount of manganese ore being processed, a concentration of less than 1% would require a large amount of hydrogen-containing gas to be supplied, which may be impractical.

A more industrial example of manganese ore-derived raw material production involves experiments on hydrogen reduction of manganese ore using an externally heated rotary kiln. A 4% hydrogen/nitrogen mixed gas was introduced into the test kiln, and the manganese ore was heated and hydrogen-reduced in the test kiln to obtain a manganese ore-derived raw material. For example, a manganese ore-derived raw material with a manganese oxidation degree of 1.1 was obtained by treating the manganese ore at 1100°C for 3 hours. The manganese oxidation degree of the manganese ore-derived raw material can be varied by adjusting the amount of hydrogen-containing gas introduced, the heating temperature, and the heating time relative to the amount of manganese ore. A higher manganese oxidation degree of the manganese ore-derived raw material shortens the hydrogen reduction treatment time and reduces the amount of hydrogen required, but reduces the _CO2 reduction effect. Conversely, as the manganese oxidation degree of the reduced manganese ore decreases toward 1.0 or closer to 1.0, the _CO2 reduction effect increases and the CO concentration in the by-product gas increases.

Another example of a more industrial production of manganese ore-derived raw material involves an experiment in which manganese ore and coke are added and reduced in an internal combustion rotary kiln. The fuel/air ratio of the internal combustion burner is set to 1.0 or less (0.96), and 7% by mass of coke is added. Treatment is carried out at 1100°C for four hours to obtain manganese ore-derived raw material. The manganese oxidation degree is 1.08. Similar results are obtained when the coke is replaced with bio-coke. Furthermore, similar results are obtained when the fuel for the internal combustion burner is replaced with biofuel.

(Manufacturing manganese alloys from manganese ore-derived raw materials)
Next, an experiment will be described in which a manganese ore-derived raw material (manganese oxidation degree = 1.1) is reduced with a carbonaceous material to produce a manganese-based alloy. In industrial practice, a submerged arc furnace or an electric furnace with equivalent functions is used to reduce a manganese ore-derived raw material with a carbonaceous material, but here, the following experiment will be described.

A manganese-based alloy is obtained by refining the manganese ore-derived raw material and coke as a carbonaceous material in a 100 kVA Giraud furnace (single-phase arc furnace), then tapping to separate and remove the molten manganese alloy (ferromanganese) from the slag. Because the Giraud furnace is an open furnace, the amount of carbon monoxide ( _CO ) generated cannot be measured. However, the manganese ore-derived raw material can be reduced with a _carbonaceous material to produce a manganese-based alloy. Furthermore, the manganese ore-derived raw material has a lower oxygen content (manganese oxidation degree) than the manganese ore, so less carbonaceous material is required. The resulting manganese-based alloy (ferromanganese) satisfies JIS G 2301.

In addition, a manganese ore-derived raw material (manganese oxidation degree = 1.05) and coke as a carbonaceous material were mixed and placed in a refractory container, and electrically heated to 1490°C in a vertical tubular furnace while circulating an inert carrier gas (nitrogen _N2 or argon Ar), and the concentration of carbon monoxide (CO) generated was measured. For comparison, a similar experiment was performed using manganese ore, and it was found that the use of the manganese ore-derived raw material resulted in a higher carbon monoxide (CO) concentration and a lower carbon dioxide (CO2 ₎ concentration.

(Synthesis of synthetic fuel using carbon monoxide contained in by-product gas as raw material)
The synthesis of synthetic fuel using carbon monoxide (CO) and hydrogen (H2 ₎ contained in by-product gas as raw materials has been proven, for example, in devices that synthesize synthetic fuel from synthesis gas ( _H2 + CO) in the GTL (Gas to Liquids) process, so it is clear that synthetic fuel can also be produced using the by-product gas of the present invention. Furthermore, since synthetic fuel is synthesized through the reaction CO + _2H2 → 1/ _nCnH2n + _{H2O ,} it can be seen that the higher the concentration (partial pressure) of carbon monoxide (CO), the easier it is to produce synthetic fuel.

In experiments, carbon monoxide (CO) generated in the above experiment and hydrogen ( _H2 ) are added, and the mixture is passed through a reaction tube equipped with a catalyst such as a Ni-based catalyst (methane production), a Cu-based catalyst (methanol production), or a Co-based catalyst (FT synthesis). The product is then analyzed using a gas chromatograph or similar device, allowing the production of synthetic fuel to be confirmed.

Based on the above, an example of an embodiment of the present invention is shown in Figure 3. High-carbon ferromanganese is produced by reducing a manganese ore-derived raw material with a manganese oxidation degree of 1.0 to 1.1 and a carbonaceous material in an electric furnace. During this process, slag and a by-product gas, CO, are generated, and the by-product gas, CO, is passed through a separately prepared synthesis device with _H2 to produce synthetic fuel.

Another example of the embodiment is shown in Figure 4. Manganese ore is passed through a gas reduction furnace with _H2 and/or CO to produce a manganese ore-derived raw material, and then the manganese ore-derived raw material and a carbonaceous material are subjected to a reduction reaction in an electric furnace to produce high-carbon ferromanganese. During this process, slag and a by-product gas, CO, are generated, and the by-product gas, CO, is passed through _a separately prepared synthesis device to produce synthetic fuel.

According to the present invention, it is possible to realize the production of carbon recovery type manganese alloys, which can achieve a significant _CO2 reduction effect, contribute to the suppression of global warming, and meet the demands for carbon neutrality and _{zero CO2} emissions.

Claims (12)

A method for producing a carbon-recovery manganese-based alloy, comprising: a step (A) of refining a manganese ore-derived raw material having a manganese oxidation degree of 1.0 to 1.1 and a carbonaceous material in an electric furnace, followed by slag-metal separation; and a step (B) of producing a synthetic fuel using carbon monoxide contained in a by-product gas generated from the electric furnace as a raw material. The method for producing a carbon-recovery manganese alloy according to claim 1, characterized in that the manganese ore-derived raw material is obtained by reducing manganese ore with hydrogen, carbon monoxide, or both hydrogen and carbon monoxide to a manganese oxidation degree of 1.0 to 1.1. The method for producing a carbon-recovery manganese alloy according to claim 1 or 2, characterized in that some or all of the carbon monoxide is carbon monoxide contained in by-product gas generated from an electric furnace. A method for producing a carbon-recovery manganese-based alloy according to any one of claims 1 to 3, characterized in that some or all of the carbon material is green carbon. The method for producing a carbon-recovery manganese alloy described in any one of claims 1 to 4, characterized in that granulated material containing the manganese ore-derived raw material and carbonaceous material is charged into the electric furnace. A method for producing a manganese-based alloy with carbon recovery according to any one of claims 1 to 5, characterized in that it also includes step (C), in which a reducing agent containing a silicon-containing ferroalloy or metallic aluminum, or both a silicon-containing ferroalloy and metallic aluminum, is added to the molten slag by-produced in step (A) to reduce at least a portion of the manganese oxide contained in the molten slag to produce a manganese-based ferroalloy. An apparatus for producing a carbon-recovery manganese alloy, comprising: means (A) for feeding a manganese ore-derived raw material having a manganese oxidation degree of 1.0 to 1.1 and a carbonaceous material into an electric furnace to perform refining, and then separating the slag from the metal; and means (B) for producing a synthetic fuel using carbon monoxide contained in a by-product gas generated from the electric furnace as a raw material. 8. The carbon recovery type manganese alloy manufacturing apparatus according to claim 7, wherein the manganese ore-derived raw material is obtained by reducing manganese ore with hydrogen or carbon monoxide, or with both hydrogen and carbon monoxide, to a manganese oxidation degree of 1.0 to 1.1. The carbon recovery type manganese alloy manufacturing apparatus according to claim 7 or 8, characterized in that some or all of the carbon monoxide is carbon monoxide contained in by-product gas generated from an electric furnace. The carbon recovery type manganese alloy manufacturing apparatus described in any one of claims 7 to 9, characterized in that some or all of the carbon material is green carbon. The carbon recovery type manganese alloy manufacturing apparatus described in any one of claims 7 to 10, characterized in that granulated material containing the manganese ore-derived raw material and carbonaceous material is fed into the electric furnace. The carbon recovery type manganese alloy manufacturing apparatus according to any one of claims 7 to 11, further comprising means (C) for introducing a reducing agent containing a silicon-containing ferroalloy or metallic aluminum, or both a silicon-containing ferroalloy and a reducing agent containing metallic aluminum, into the molten slag by-produced in means (A) to reduce at least a portion of the manganese oxide contained in the molten slag to produce a manganese-containing ferroalloy.