JPS6214209B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing ferrochrome by melting and reducing chromium ore using a rotary furnace. Conventionally, ferrochrome was produced by charging chromium ore with a reducing agent such as coke and a slag-forming agent such as limestone into an electric furnace and refining it in an electric furnace, which consumed a large amount of electricity. This was considered a serious problem from the viewpoint of resource conservation and economic efficiency. The present inventors have conducted intensive research to solve the above-mentioned problems and develop a method for producing ferrochrome that can replace the conventional electric furnace smelting process. Invented a method of
I did this. In this method, chromium ore is fed together with a reducing agent and a slag-forming agent into a rotary furnace whose axis is horizontal or gently inclined, and the chromium ore is melted and reduced by blowing oxygen or oxygen-enriched air into it. On the other hand, high-temperature exhaust gas discharged from the rotary furnace is guided to a rotary kiln, and the chromium ore to be supplied to the rotary furnace is preheated in the rotary kiln. According to this method, ferrochrome can be produced economically without using a large amount of expensive electricity for refining. The present inventors conducted research on an economical operating method that would reduce the amount of corrosion of the refractory lining of the rotary furnace and recover metal at a high rate when manufacturing ferrochrome using the batch method described above. I did it. The refining process of ferrochrome in a rotary furnace is as follows:
When this is operated in a batch type, the following three stages are distinguished depending on the state of the raw materials supplied into the furnace. (a) Melting period This is the early stage of refining, when raw materials are melted and some of them are reduced. (b) Smelting reduction period This is the middle stage of refining, when the undissolved phase of the raw material dissolves and reduction ends. (c) Separation stage This is the final stage of refining, when the metal particles suspended in the slag separate and settle, forming agglomerates. According to the research conducted by the present inventors, in order to suppress the erosion of refractories and perform refining in each of the above stages stably and efficiently, the composition of the slag should be adjusted according to the characteristics of each stage as described below. It was found that it was necessary to control the (b) Melting period The raw materials supplied into the furnace are melted at the optimum melting temperature of 1500 to 1600℃, as shown in the temperature rise pattern of the rotary furnace in Figure 1, and the refractory is melted during melting. In addition, the composition is formulated so that the amount of sludge forming agent added is as small as possible. (b) Smelting and reduction period The composition of the molten slag in the furnace is adjusted so that the slag maintains a certain degree of fluidity in order to prevent erosion of refractories and ensure stable operation. (c) Separation period The composition of the molten slag in the furnace is adjusted so that the metal and slag are well separated and the amount of S in the metal is reduced. This invention was made based on the above knowledge, and includes the following steps: Chromium ore is supplied together with a reducing agent and a slag-forming agent into a rotary furnace whose axis is horizontal or gently inclined, and oxygen is blown into the rotary furnace. In the method for producing ferrochrome in which ferrochrome is produced by a batch method by melting and reducing chromium ore, the operating conditions are divided into a melting period, a melting reduction period, and a metal/slag separation period, and in the melting period, The raw materials supplied into the furnace are CaO, SiO ₂ ,
The difference between the liquidus temperature and the dissolution temperature on the quaternary system phase diagram of MgO and Al ₂ O ₃ is within the range of (-50℃) to (+250℃), and the basicity is 1.3 to 2.0. In the smelting and reduction period, the composition of the molten slag in the furnace is set such that the difference between the liquidus temperature and the melting temperature on the four-element phase diagram is between (-50°C) and (-50°C) to ( +400
℃) by adding MgO-based and CaO-based slag forming agents at a ratio of MgO/CaO of 80/20 to 20/80. The basicity of molten slag is 1.3~
It is characterized by operating while keeping it within the range of 2.0. Next, the reason why the operating conditions in this invention are limited as described above will be explained. (b) Melting period Table 1 shows the melting point of the raw material, that is, the melting temperature, the raw material composition of the slag component necessary to melt at that temperature, and the amount of slag-forming agent added. CaO, SiO ₂ , MgO and Al ₂ O ₃ in the gangue main components contained in the chromium ore at that time
and the content of said components in the final slag. As can be seen from Table 1, the melting temperature of the raw materials is
If the raw material composition is lower than 1500℃, the amount of slag forming agent added will be large, and as a result, the relationship between the raw material melting temperature, the amount of slag forming agent, the amount of refractory erosion and the amount of heat required during melting as shown in Figure 2. As can be seen from the graph showing the relationship, the amount of erosion of the refractory increases, and the amount of heat of dissolution of the slag agent also increases. On the other hand, if the raw material composition is such that the melting temperature of the raw materials exceeds 1600°C, the amount of erosion of the refractory becomes large again, as can be seen from Figure 2. Furthermore, if the raw material composition is such that the melting temperature of the raw materials exceeds 1600°C, the briquette state in the furnace will be prolonged for a long time, as can be seen from the raw material melting state by temperature and exhaust gas composition change state diagram in Figure 3. It takes a long time to dissolve the raw materials, resulting in low O ₂ efficiency and high energy requirements. Therefore, the raw materials supplied into the column should have a blending composition such that their melting point, ie, melting temperature, is 1500 to 1600°C.

【table】

[Table] As mentioned above, in order to melt the raw materials at 1,500 to 1,600°C, the composition must be determined according to the four-element system phase diagram of CaO, SiO ₂ , MgO, and Al ₂ O ₃ shown in Figure 4. The difference between the liquidus temperature and the melting temperature (liquidus temperature - melting temperature on the phase diagram) is (-50℃) to (+250℃)
It is necessary to keep it within the range of . That is, as can be seen from the relationship between the liquidus temperature and melting temperature on the four-element phase diagram shown in Fig. 5 and the melted state of the raw material, the difference between the liquidus temperature and the slag phase temperature on the phase diagram is -50°C. If the temperature exceeds 250°C, the refractory material will suffer significant melting damage.
If the amount exceeds , it becomes difficult for the raw material to dissolve,
Moreover, the fluidity of the melt is poor, resulting in a problem of lack of operational stability. In addition, in the same figure, the dashed-dotted line indicates the line where the liquidus temperature and the melting temperature on the phase diagram match. In addition, the basicity (CaO/
SiO ₂ ) needs to be within the range of 1.3 to 2.0. That is, as can be seen from the relationship between the basicity of slag during raw material melting, the amount of refractory erosion, the amount of slag-forming agent added, and the total cost of refractory and slag-forming agent, as shown in FIG. When the degree is less than 1.3, the amount of slag-forming agent added is small, but the amount of refractory erosion increases, so the total cost of refractory and slag-forming agent increases. On the other hand, when the basicity exceeds 2.0, the amount of refractory erosion is small, but the amount of slag-forming agent added increases, so the total cost of the refractory and slag-forming agent increases. Table 3 shows the relationship between the basicity of the raw material composition and the amount of slag-forming agent added.
It can be seen that when the value exceeds 2.0, the amount of slag forming agent added increases. (b) Smelting and reduction period In the smelting and reduction period, the molten slag in the furnace during the heating stage of the furnace is adjusted to the liquidus temperature and melting temperature on the four-element system phase diagram of CaO, SiO ₂ , MgO, and Al ₂ O ₃ The difference between (liquidus temperature - melting temperature on the phase diagram) is (-50℃)
It is necessary to maintain the composition within the range of ~(+400°C). Figure 7 shows the difference between the liquidus temperature and the melting temperature on the above phase diagram, the slag viscosity, and the slag content.
A graph showing the relationship with the increase in MgO content.
As can be seen from the figure, the difference between the liquidus temperature and the melting temperature on the phase diagram is

[Table] When the temperature exceeds −50℃, MgO in the slag increases.
The content, ie, the amount of refractory erosion, increases, and on the other hand, if the temperature difference exceeds +400°C, the viscosity of the slag increases and its fluidity deteriorates. In order to adjust the slag composition to be within the above range, use MgO-based and CaO-based sludge-forming agents such as limestone, dolomite, and magnesia, with an MgO/CaO ratio of 80/20 to 20, as shown in Figure 4. Add them to the furnace in appropriate combinations at a ratio of /80.
If the MgO/CaO ratio of this slag agent exceeds 80/20, it becomes difficult to dissolve the sludge agent;
If the CaO ratio is less than 20/80, the refractory will suffer significant erosion due to the decrease in MgO content. (c) Separation stage The basicity of the final slag in the separation stage is 1.3.
It is necessary to keep it within the range of ~2.0. That is, as can be seen from the relationship diagram between the slag basicity and the amount of S in the metal shown in Figure 8, when the basicity is less than 1.3, the S content in the metal is large; If it exceeds 2.0, the separation of slag and metal will become poor and the metal recovery rate will decrease. Next, the present invention will be explained based on examples. Horizontal with an internal diameter of 1 m and a length of 1.5 m, lined with magnesia chrome refractory to a thickness of 500 mm.
High carbon ferrochrome was produced using a rotary furnace tilted at 20° and rotating at a speed of 8 revolutions per minute. First, chromium ore preheated to 500℃, a slag-forming agent, and a reducing agent are added to the rotary furnace as raw materials in the
Supplied as shown in the table.

[Table] Then, oxygen was sprayed onto the raw material in the furnace as shown in the refining pattern diagram in FIG. 9 using a water-cooled lance inserted from the furnace mouth. As a result, the raw material reached 1600°C and melted 30 minutes after spraying started. When the slag was sampled immediately after melting and analyzed, its component composition was as shown in Table 5.

[Table] Prior to melting the raw materials, coke is added to the furnace at a rate of 10 kg/min for approximately 20 minutes approximately 10 minutes after the start of blowing. A layer of coke was formed. After melting the raw materials, a slag-forming agent containing calcined dolomite and magnesia clinker mixed at a ratio of 3:2 was added at a rate of 10 kg/min in the pattern shown in Figure 8 to adjust the composition of the slag. . As a result, the composition of the slag was controlled as shown in FIG. Approximately 55 minutes after starting blowing, the temperature of the slag reached 1700.
℃ reached. Therefore, the addition of slag-forming agent was stopped and the rotation speed of the furnace was lowered to 3 rpm to calm the molten metal in the furnace. About 70 minutes after the start of blowing, the blowing was completed and the hot water was tapped. The slag temperature at the time of tapping was 1700°C, and the weight and composition of the metal and slag were as shown in Tables 6 and 7.

【table】

[Table] The amount of refractory corrosion inside the furnace was 48 kg. As described above, when manufacturing ferrochrome by melting and reducing chromium ore in batches using a rotary furnace according to the method of the present invention, the amount of corrosion of refractories is small, metal can be recovered at a high rate, and Only a small amount of the slag agent is added, and excellent industrial effects are brought about, such as being able to stably produce ferrochrome of excellent quality with a low S content.

[Brief explanation of the drawing]

Figure 1 shows the temperature increase pattern of the rotary furnace, Figure 2 shows the temperature increase pattern of the rotary furnace.
The figure is a graph showing the relationship between the raw material melting temperature, the amount of slag-forming agent, the amount of refractory erosion, and the amount of heat of dissolution. Figure 3 is a state diagram of exhaust gas composition in the refining process. Figure 4 is
Quaternary system phase diagram of CaO, SiO ₂ , MgO, Al ₂ O ₃ , Part 5
The figure shows the relationship between the liquid phase temperature and slag phase temperature on the four-element phase diagram and the melting state of raw materials. Figure 6 shows the basicity of slag during melting, the amount of refractory erosion, the amount of slag-forming agent added, etc. Figure 7 is a graph showing the relationship between the difference between liquidus temperature and slag temperature on the phase diagram, slag viscosity and increase in MgO content in slag, and Figure 8 is a graph showing the relationship between slag base and slag temperature. FIG. 9 is a diagram showing the relationship between the degree of oxidation and the amount of S in the metal, and FIG. 9 is a blowing pattern diagram showing an embodiment of the present invention.

Claims (1)

[Claims] 1. Into a rotary furnace where the axis of the furnace is horizontal or gently inclined,
Supplying chromium ore with reducing agent and slag forming agent,
In the method for producing ferrochrome in which ferrochrome is produced by a batch method by melting and reducing chromium ore by blowing oxygen into it, the operating conditions are divided into a melting period, a melting reduction period, and a metal/slag separation period, In the melting period, the raw materials supplied into the furnace are CaO, SiO ₂ ,
The difference between the liquidus temperature and the dissolution temperature on the quaternary system phase diagram of MgO and Al ₂ O ₃ is within the range of (-50℃) to (+250℃), and the basicity is 1.3 to 2.0. In the smelting and reduction period, the composition of the molten slag in the furnace is set such that the difference between the liquidus temperature and the melting temperature on the four-element phase diagram is between (-50°C) and (-50°C) to ( +400
℃) by adding MgO-based and CaO-based slag forming agents at a ratio of MgO/CaO of 80/20 to 20/80. The basicity of the internal molten slag is 1.3
A method for producing ferrochrome, characterized in that the operation is performed while maintaining the ferrochrome within the range of ~2.0.