JPH0428775B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high carbon ferrochrome by reducing and smelting chromium ore reduced sintered pellets in a buried arc electric furnace. Usually, high carbon ferrochrome is manufactured by charging chromium ore, sintered chromium ore, or reduced sintered chromium ore into an electric furnace together with flux, and reducing it with a carbonaceous reducing material (hereinafter referred to as carbonaceous material). In the electric furnace method, chromium oxide and iron oxide components in chromium ore are reduced with carbonaceous material, and MgO,
High carbon ferrochrome metal is obtained by separating Al ₂ O ₃ , SiO _{2 ,} etc. (hereinafter referred to as gangue components) as molten slag. Chromium ore reduced and roasted pellets are made by blending chromium ore with carbonaceous materials to form pellets, and then partially reducing and roasting the metal components in a solid state using a rotary kiln, etc. The unreduced portion is roasted in an electric furnace. Then, reduction smelting is performed. However, the main purpose of using reduced chromium ore sintered pellets is to rely entirely on cheap combustion energy for the required energy and to reduce expensive electrical energy. Therefore, the sensible heat imparted to the pellets in the reduction roasting process is transferred to the electric furnace smelting process without being lost, and at the same time, the reduction rate achieved in the reduction roasting process is transferred to the reduction smelting process in the electric furnace. must be maintained until In particular, chromium has an extremely high affinity for oxygen, and requires high temperatures to reduce its oxide at normal pressure. On the other hand, the chromium metal phase or carbide phase produced by solid phase reduction is extremely easily reoxidized in an oxidizing atmosphere. The reaction products from the solid phase reduction of chromium ore are mainly chromium/iron carbides ((Cr, Fe) ₇ C ₃ etc.), but these carbides are not only present in oxygen atmosphere but also in carbon dioxide (CO ₂ ) and water vapor (H ₂ ). In an atmosphere that has an oxidizing effect on chromium/iron carbides, such as O) or sulfur dioxide (SO ₂ ), a reoxidation reaction easily occurs, forming chromium/iron oxides according to the following formula.
In this case, the reoxidation of chromium is particularly significant. (Cr, Fe) ₇ C ₃ +27/4O ₂ =7/2 (Cr, Fe) ₂ O ₃ +3CO (1) (Cr, Fe) ₇ C ₃ +27/2CO ₂ =7/2 (Cr, Fe) ₂ O ₃ +33/2CO (2) (Cr, Fe) ₇ C ₃ +27/2H ₂ O =7/2 (Cr, Fe) ₂ O ₃ +3CO+27/2H ₂ (3) (Cr, Fe) ₇ C ₃ +27/ 2SO ₂ = 7/2 (Cr, Fe) ₂ O ₃ + 3CO + 27/2CO (4) The above reaction progresses more rapidly at higher temperatures, so in the process of producing high carbon ferrochrome, red-hot reduced sintered pellets are Care must be taken to reduce the number of machines that come into contact with the oxidizing atmosphere. Regarding the prevention of re-oxidation of chromium ore reduced sintered pellets, methods have been proposed, such as transferring them to a non-oxidizing atmosphere immediately after roasting and cooling them, but this method is not practical as it requires bulky equipment and is complicated to handle. The above has many disadvantages. In general, the red-hot pellets produced in the reduction roasting process are transferred to a red-hot pellet tank as quickly as possible, isolated from the atmosphere as much as possible, and transferred to the electric furnace reduction process. In normal reduction sintered pellets, re-oxidation is suppressed due to the effect of the oxide film layer present on the pellet surface, and the reduction rate achieved in the reduction roasting process is substantially maintained until the pellet is transferred to the electric furnace reduction process. It is transitioning. However, when an external force such as a drop impact, compressive force, or thermal stress is applied to the pellet during the production process, the oxide film layer on the pellet surface is destroyed, resulting in cracks or cracks in the pellet.
When such a pellet is formed, the reduction product phase inside the pellet is newly exposed, and when it comes into contact with an oxidizing atmosphere, reoxidation proceeds rapidly. As a result of a detailed study of the behavior of red-hot pellets in the high carbon ferrochrome production process, the present inventors found that
By creating strong pellets, eliminating external forces that could lead to pellet destruction, and minimizing the coexistence of an oxidizing atmosphere that has an oxidizing effect on reduction products, we have reduced the power consumption required for ferrochrome production. They have discovered that this can be dramatically improved, and have devised the present invention. The present invention is a method for producing high carbon ferrochrome using chromium ore reduced sintered pellets, in which water vapor that can lead to destruction of pellets is removed in the process of handling red-hot pellets, and water vapor (which has an oxidizing effect on reduction products) is removed. This is achieved by eliminating H ₂ O) and carbon dioxide (CO ₂ ) gases. More specifically, the present invention dries the carbon material and slag-making material charged into an electric furnace together with red-hot chromium ore reduced sintered pellets to remove moisture brought in, and the slag-making material is thermally decomposed. This is achieved by using slag, avoiding those containing carbonates, which generate _CO2 . Next, the present invention will be explained in detail. Maintaining a proper slag composition is very important in electric furnace operation. Conditions for good slag include good fluidity, appropriate melting point, high electrical resistance, promotion of chromium reduction, and high distribution of impurity components. . If these selections are made incorrectly, not only will it not be possible to obtain a product of the desired quality, but if the power consumption rate deteriorates significantly, it may lead to operational difficulties. Chromium ore contains MgO and Al ₂ O ₃ as gangue components.
Contains SiO ₂ and the like, and the content of these varies widely depending on the ore's origin. Among these, SiO ₂ is contained in relatively small amounts, while MgO and Al ₂ O ₃ are mainly in the form of pichromite (Mg, Fe) O (Cr, Fe, Al) ₂ O ₃ with a spinel structure. Since it exists, it is contained in relatively large amounts. On the other hand, in electric furnace smelting, MgO−Al ₂ O ₃ −CaO−
The SiO ₂ -based quaternary slag must be selected, and a composition that satisfies melting point, adhesion, electrical resistance, impurity distribution coefficient, etc. must be selected. The composition ranges usually selected are _SiO2 ; 27-33%, CaO; 9-14%, MgO; 23%.
-33%, _Al2O3 ; _20-35 %. MgO _{, Al2O3}
If this increases, the melting point of the slag will increase and the viscosity will also increase, which is not preferable. However, since MgO and Al ₂ O ₃ are determined automatically depending on the ore used, SiO ₂ and CaO components are usually used as slag forming materials, and in some cases, the MgO component may be adjusted. There is also. The composition range of the slag used in the present invention is
CaO: 40-55%, _SiO2 : _25-35 %, _Al2O3 : 10%
The reason for limiting the composition to the following is that if the composition falls outside this range, it becomes necessary to further add one or both of the CaO component or SiO ₂ component in order to maintain the slag composition in the electric furnace within the above-mentioned appropriate reaction range. This is because the total amount of slag increases, which is disadvantageous. Furthermore, the S component is limited to 0.5% or less because if slag with a high S component is used, the S distribution in the slag will reach saturation and the S content in the high carbon ferrochrome product will become high. Furthermore, the reason for using slag is to use a slag material with a low carbonate content. Silica is commonly used as the SiO ₂ component. Silica stone contains 96 to 98% of SiO ₂ components, and if it is managed with adhering moisture, there are very few components that involve endothermic reactions such as crystal water and carbonates, and components that have an oxidizing effect on chromium reduction products. . On the other hand, there is quicklime as a CaO component.
Although it is preferable because it contains 95% or more of CaO, it has drawbacks such as being expensive and being inconvenient to handle because it reacts with moisture and generates heat. Coal stone is also widely used as an inexpensive CaO source. However, coal stone emits CO ₂ due to endothermic reactions.
This is undesirable because it generates chromium ore and re-oxidizes the reduced chromium ore sintered pellets. In addition, dolomite, serpentine, ferronite slag, etc. can be used as the slag material for adjusting the slag components. Among these, dolomite forms carbonates and decomposes
Like coal stone, it is undesirable because it generates CO ₂ gas. Also, serpentinite contains about 13% water of crystallization, which is undesirable because it decomposes and generates H ₂ O. As long as the adhering moisture is controlled, fluorite slag does not contain anything that re-oxidizes the reduced chromium ore sintered pellets, so it can be used as _two components of MgO and SiO. The present inventors investigated various inexpensive slag-making materials that are rich in SiO ₂ and CaO components, have low content of adhering moisture, crystal water, carbonates, etc., and found that slag and low-carbon slag produced in the stainless steel manufacturing process The present invention was completed based on the discovery that the base slag produced in the ferrochrome smelting process has the necessary quality. In other words, the slag generated in the stainless steel manufacturing process is
Usually CaO; 40-55%, _SiO2 ; 25-35%,
Contains MgO: 10-20% _{, Al2O3} : 1-5%, and does not contain crystal water or carbonate. Further, the reason why stainless steel slag is particularly useful is that the Al ₂ O ₃ component is relatively low at 5% or less. If the Al ₂ O ₃ component is small, less SiO ₂ and CaO components need to be added, which makes it possible to reduce the total amount of slag in the smelting process, which is effective in reducing electricity consumption. A further advantage is that stainless steel slag contains fewer components harmful to ferrochrome smelting, such as S and P ₂ O ₅ . Components such as Cr ₂ O ₃ and FeO pose no particular problem. Low carbon ferrochrome smelting slag is generally CaO; 40
~50%, _SiO2 ; 27-30%, MgO; 10-13%,
It contains 5 to 10% of Al ₂ O ₃ and almost no crystal water or carbonate. Except for the fact that Al ₂ O ₃ is slightly higher than that of stainless steel slag, the objects of the present invention can be fully achieved. If these slags are carefully managed before use, they can be obtained and used in a state that contains almost no attached water. Next, we will give an example in which the present invention is applied to high carbon ferrochrome refining using chromium ore reduced sintered pellets, and for comparison with the conventional method, an example in which fluorescent light and coal stone are used as slag materials. The present invention will be explained by comparing with the following. Example 1000 parts of chromium ore and coke with the composition shown in Table 1
216 parts were mixed and pulverized, pentonite was added as a binder, and an appropriate amount of moisture was added to granulate, followed by drying.

[Table] The obtained dried pellets were charged into a rotary kiln and subjected to reduction roasting at a maximum reduction temperature of 1450°C. The analytical values of the obtained reduced crystal pellets were as shown in Table 2.

[Table] In Table 2, T.Cr and T.Fe represent the total chromium and total iron in the pellet, respectively, and Sol.Cr and Sol.Fe represent chromium and iron that are soluble in acids. . The red-hot reduced sintered pellets discharged from the rotary kiln were transported in a red-hot pellet container directly below the kiln, and charged through the feed chute of the electric furnace. At that time, 100 parts of dry lump coke per 1000 parts of red-hot pellets and stainless steel slag were used as reducing materials and slag-forming materials necessary for electric furnace reduction.
130 parts and some silica to adjust basicity were added onto the pellets in the red hot pellet container. The composition of the stainless steel slag used as the slag material was as shown in Table 3. Inside the red-hot pellet container, the pellets were covered with carbon and slag material to block contact between the pellets and the atmosphere, and to prevent the red-hot pellets from being cooled down and re-oxidized.

[Table] The electric furnace used for reduction refining was an 18,000 KVA closed buried arc furnace, and was operated by continuously supplying raw materials. Table 4 shows the reactor operation results and the analytical values of the high carbon ferrochrome obtained.

[Table] Comparative Example The same reduced sintered pellets as in the above example were used, and silica stone and coal stone were used as slag materials. The mixing ratio was 1000 parts of reduced sintered pellets, 105 parts of lump coke, 55 parts of silica stone, and 130 parts of coal stone. The operating results of the electric furnace and the obtained high carbon ferrochrome metal quality are also listed in Table 4. As is clear from the furnace operation results, when stainless steel slag is used as the slag making material, the electric power consumption rate is greatly improved, indicating that the present invention is economically extremely useful.

Claims (1)

[Claims] 1. In producing high carbon ferrochrome by smelting reduced chromium ore sintered pellets in an electric furnace,
CaO40 _~ 55%, _SiO2 25~35%, _Al2O3 10% or less,
A method for producing high carbon ferrochrome, characterized by using slag containing 0.5% or less of S.