JPH032933B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high-carbon ferrochrome using a shaft-type smelting furnace using a pre-reduced product of chromium ore as a raw material, which is highly efficient and consumes less energy than conventional methods.
The aim is to establish a smelting method with low equipment costs and high throughput. Conventionally, high-carbon ferrochrome has been manufactured using the so-called electric furnace smelting method, which uses chromium ore as the main raw material, supplies the energy necessary for reduction reactions, melting, etc. with electricity, and uses coke as a reducing agent. In the production of high carbon ferrochrome in this electric furnace smelting, approximately 3,750 to 4,000 KWH of electricity is consumed per 1 ton of high carbon ferrochrome, so the electricity cost that accounts for a very large portion of the product cost is unavoidable, making the product cost rise unavoidably. . Regarding this electric furnace method as well, various studies were conducted to reduce the amount of expensive electrical energy used in order to reduce energy costs, and as a result, a method was proposed in which chromium ore was pretreated and then treated in an electric furnace. . For example, in Japanese Patent Publication No. 48-37885, chromium ore and a carbonaceous reducing agent are pulverized and mixed, then molded, the molded product is charged into a rotary kiln together with a carbonaceous material, and heated and reduced to produce a pre-reduced chromium ore molded product. There is a method of charging this pre-reduced molded product into an electric furnace and smelting it. Another method is to mold chromium ore and charge the fired sintered product into an electric furnace in the form of a heating material to smelt it. However, chromium smelting requires a smelting temperature of 1,600℃ or higher because chromium has a higher melting point than iron or manganese, so in the end, it is necessary to use an electric furnace for melting and smelting. When using the chromium ore pre-reduced molded product and charging it directly from a rotary kiln to an electric furnace at a temperature of approximately 1000℃, the electric power consumption is approximately
2000KWH/t product. Pre-treating chromium ore in this way has shown great effects in reducing energy costs, but as long as an electric furnace is used, there is a limit to the reduction in energy costs. On the other hand, in Europe and the United States, attempts have been made to produce ferrochrome using blast furnaces, but the ferrochrome produced has a relatively low melting point with a chromium content of approximately 10 to 40%, and is called chromium-containing pig iron. Moreover, the consumption of coke for reduction and heating is very large, making it not an economical method. Currently, iron and manganese-based alloys are manufactured using the above-mentioned blast furnace or shaft furnace, but chromium is difficult to undergo ring reduction compared to the above-mentioned iron and manganese, and the reduction reaction is expressed by the following equation. As shown, this is an extremely endothermic reaction. Cr ₂ O ₃ 2Cr＋3/2O ₂ −△H ₂₉₈ = 270.0Kcal/mol FeOFe＋1/2O ₂ −△H ₂₉₈ = 63.0Kcal/mol MnOMn＋1/2O ₂ −△H ₂₉₈ = 92.0Kcal/mol Therefore, the production of chromium Refining requires extremely severe reaction conditions and requires high temperatures as mentioned above, making it impossible to produce ferrochrome containing high chromium using a blast furnace or shaft furnace. As a result of a detailed study on the above, the present inventor has discovered that the heat absorption due to the reduction reaction of chromium can be reduced using the pre-reduced chromium ore molded product currently used in the electric furnace smelting process, and that it can be further applied to shaft furnaces. The chromium content is reduced in shaft-type smelting furnaces by supplying heated air or even oxygen-enriched it.
The present invention was completed after discovering that ferrochrome with a carbon content of 50% or more can be efficiently produced. The present invention has a chromium content of 50% without using an electric furnace.
The purpose of this project is to establish a method for industrially producing high-carbon ferrochrome with low energy consumption and efficiency, and to provide a method for producing high-carbon ferrochrome using a shaft-type smelting furnace. be. In other words, the present invention achieves a chromium reduction rate of 30% when smelting high carbon ferrochrome from chromium ore.
As described above, the pre-reduced chromium ore molded product with an iron reduction rate of 50% or more, the necessary slag-forming agent, and coke for reduction and heating are charged into a shaft furnace, and preheated air or preheated oxygen enrichment is charged into the shaft furnace. This is a method for producing high carbon ferrochrome, which is characterized by supplying air for smelting. The present invention will be explained in detail below. The equipment used to carry out the present invention is a shaft-type smelting furnace including a hot air cupola, a low shaft furnace, a small blast furnace, and the like. When using a blast furnace, which is conventionally used for iron smelting, it is possible to use low-strength, low-grade coke by making some modifications, such as lowering the height of the shaft, which has a large economic effect. . Next, the chromium ore used in the method of the present invention is a pre-reduced product, with a chromium reduction rate of 30% or more,
It has an iron reduction rate of 50% or more. Pre-reduced chromium ore moldings are currently produced industrially for use in the production of high-carbon ferrochrome by electric furnace smelting.Chromium ore and carbonaceous reducing agents are pulverized and mixed, then molded, and the molded products are processed in a rotary kiln. It is produced by charging it together with carbonaceous materials and heating and reducing it. In the present invention, if the reduction rate of the chromium ore pre-reduced molded product is less than 30% for chromium and less than 50% for iron, the effect of reducing the amount of heat absorbed by the reduction reaction in the shaft furnace is small, resulting in insufficient temperature. , the state of hot water discharged from the shaft furnace becomes unstable, and the separation of metal and slag becomes poor, making normal operation impossible. Therefore, the chromium ore pre-reduced molded product has a chromium reduction rate of 30% or more and an iron reduction rate of 50% or more. You need to use the one. As the main raw material, an iron source such as scrap or pig iron can be mixed with the chromium pre-reduced molded product. When iron scrap is supplied to a shaft-type smelting furnace, it is carburized and becomes pig iron, which has good meltability and increases the production amount of high-carbon ferrochrome. A mixture of the pre-reduced molded product, a slag-forming agent, and a carbonaceous material for thermal reduction are charged into the shaft furnace from the top of the furnace. At this time, it is preferable to charge the mixture and the carbonaceous material alternately in layers. Slag-forming agents vary depending on the content of gangue components such as SiO ₂ , Al ₂ O ₃ , and MgO in the pre-reduced chromite, but are usually appropriately sized silica, limestone, quicklime, or serpentine. Rocks are used. As the carbon material for thermal reduction, metallurgical coke, soft coke with low crushing strength, small lump coke, oil coke, and charcoal can be used. It is not necessary to use only coke. In the operation of the method of the present invention, bed coke is first charged into the bottom of a shaft-type smelting furnace, and air is blown to burn part of this coke to raise the temperature inside the furnace. After reaching the temperature, the above raw materials are charged. The amount of air blown through the tuyere of the shaft-type smelting furnace during continued operation must be 20 to 80 Nm ³ /min of oxygen per 1 m ² of cross-sectional area inside the tuyere surface furnace, and additional air must be used. In this case, it is necessary to preheat to 600℃ or higher. If the amount of air is less than 20 Nm ³ /min as the amount of oxygen per 1 m ² of cross-sectional area in the tuyere surface of the furnace, the calorific value is small, resulting in insufficient temperature and operation becomes impossible. Furthermore, if the oxygen amount is 80 Nm ³ /min or more, a corresponding amount of heating coke is required, which increases the coke consumption rate and increases the cost. Therefore, the amount of air is equal to the cross-sectional area of the tuyere surface of the shaft-type smelting furnace.
The amount of oxygen per m ² needs to be within the range of 20 to 80 Nm ³ /min, and is adjusted as appropriate depending on the temperature situation in the shaft furnace. Further, the reason why the preheating temperature of the air is set to 600° C. or higher is to maintain high temperature operation necessary for carrying out the method of the present invention. That is, the coke is burned near the tuyere, the pre-reduced chromite is rapidly melted, the unreduced chromium oxide and the coke are rapidly reacted, and the temperature of the metal and slag is raised to 1600°C or higher. This is to facilitate tapping and separation of slag and metal. If the preheating temperature was below 600°C, it would be impossible to obtain the high temperature necessary for smelting high carbon ferrochrome, making operation impossible, so the air preheating temperature was set at 600°C or above. Furthermore, oxygen can be mixed with the air blown into the tuyere of the shaft furnace and blown in as so-called oxygen-enriched air. Even in the case of this oxygen-enriched air, the above-mentioned required amount of charged oxygen does not change significantly, so the total amount of air blown from the tuyeres decreases, and the amount of exhaust gas also decreases accordingly. This means that the amount of heat required to heat the blown air and the amount of heat carried away by the exhaust gas is reduced, and the preheating temperature of the oxygen-enriched air can be lowered. Even in the case of oxygen-enriched air, if the preheating temperature of the blown gas is below 200°C, there will be a lack of heat, making operation difficult. Next, in the method of the present invention, after taking out the chromite pre-reduction molded product from the rotary kiln,
Depending on the situation, it is possible to use the raw material as it is or in a cooled state, or to preheat the raw material using the heat of the exhaust gas generated from the shaft-type smelting furnace. All are included within the scope of the present invention. Next, the present invention will be explained with reference to examples. Example 1 The chromite pre-reduced moldings used were produced by a conventional method currently produced for use in electric furnace processes. For example, Tokko Akira
48-37885, chromium ore and a carbonaceous reducing agent are crushed, bentonite and an organic binder are added thereto, mixed, granulated and dried, and heated and reduced in a rotary kiln at a temperature of approximately 1350℃. be. Its component composition is shown in Table 1, with a chromium reduction rate of 58.2% and an iron reduction rate of 93.7%. The compositions of other raw materials used are also shown in Table 1.

【table】

[Table] The shaft type smelting furnace used has a tuyere surface inner diameter of 550
It is a hot air cupola with an effective height of 2750 mm and a tuyere ratio of 14.5 mm. Bed coke was charged in advance into the hot air cupola, and air preheated to 800°C was blown to burn the coke and raise the temperature inside the furnace. A mixed raw material of the pre-reduced chromite, silica stone and quicklime was charged into the furnace, followed by coke, and then both raw materials were alternately charged into the furnace in layers. During operation, the air blown into the furnace was preheated to 780°C to 800°C and blown through the tuyeres at a flow rate of 45Nm ³ /min.
As a result of continuing the operation as described above, 0.87 t of high carbon ferrochrome and 0.81 t of slag were obtained per hour. Its component composition is shown in Table 2.

[Table] The hot water supply temperature at the time of tapping the high carbon ferrochrome and slag was about 1650°C, and the temperature of the exhaust gas from the top of the furnace was 550°C to 600°C. Note that this exhaust gas was used to preheat the blown air. High carbon ferrochrome obtained from the above experiment
The raw material consumption per ton is shown in Table 3, and the chromium yield was 94.6%, which was superior to the conventional electric furnace method.

[Table] Based on the coke consumption shown in Table 3, when comparing the energy consumption with the conventional electric furnace method that also uses chromite pre-reduced moldings, it is found that the energy consumption is reduced by 15%, and the energy consumption is reduced by 15%. Since coke is used in this process, energy costs can be reduced even more. Example 2 A high-temperature chromite pre-reduction molded product discharged from a rotary kiln was used immediately without cooling (charging temperature to a hot air cupola was approximately 800°C), and Example 1
It was operated in a manner similar to that described in . As a result, 0.95 tons of high carbon ferrochrome was produced per hour of operation, improving productivity by approximately 10%. Example 3 As the raw materials used, a chromite pre-reduced molded product with a chromium reduction rate of 30.2% and an iron reduction rate of 55.2% and other raw materials shown in Table 1 were used, and the preheating temperature of the blown air was 600°C. Blow air amount to 41Nm ³ /min
It was smelted using the same equipment and the same operating procedure as in Example 1. As a result, the amount of metal tapped per hour of operation was 0.78t of high carbon ferrochrome and 0.75t of slag, and the temperature of the molten metal at the time of tapping was approximately 1600℃, which is the limit of the temperature at which the metal and slag can be separated after tapping. It was hot. Additionally, the chromium yield decreased to approximately 90% and the coke consumption rate increased to 760 kg. The compositions of the high carbon ferrochrome and slag obtained are shown in Table 4.

[Table] Example 4 Using the same raw materials and the same operating conditions as in Example 3, oxygen-enriched air was blown by mixing 10% oxygen with the air blown from the tuyere of the furnace. As a result, it was possible to lower the preheating temperature of the oxygen-enriched air to 420°C, and almost the same results were obtained. As is clear from the above results, according to the method of the present invention, it is possible to reduce the energy consumption rate and energy cost for producing high carbon ferrochrome, and it is also possible to smelt high carbon ferrochrome using a conventional electric furnace. This method is very superior compared to other methods.

Claims (1)

[Claims] 1. In smelting high carbon ferrochrome from chromium ore, the chromium ring element rate is 30% or more and the iron reduction rate is 50%.
% or more of pre-reduced chromite, together with the required slag-forming agent and coke for reduction and heating, are charged into a shaft furnace, and preheated air or preheated oxygen-enriched air is supplied to the shaft furnace. A method for producing high carbon ferrochrome, which is characterized by smelting. 2. The amount of oxygen in the air or the oxygen-enriched air supplied to the shaft furnace is 20 to 80 Nm ³ /min per 1 m ² of cross-sectional area in the tuyere surface of the shaft furnace.
The manufacturing method according to claim 1, which is within the scope of. 3. The manufacturing method according to claim 1 or 2, characterized in that the preheating temperature of the air supplied to the shaft furnace is 600° C. or higher. 4. The manufacturing method according to claim 1 or 2, characterized in that the preheating temperature of the oxygen-enriched air supplied to the shaft furnace is 200° C. or higher. 5. The manufacturing method according to claims 1 to 4, characterized in that an iron source is mixed into the pre-reduced molded product as a raw material.