JPS6250543B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention recovers the chromium content by inexpensively and efficiently reducing chromium oxide-containing products such as slag, dust, and sludge during stainless steel manufacturing, and reduces the amount of products that are discharged outside the system. The present invention relates to a method for reducing chromium content to significantly lower levels. In the stainless steel melting process, some of the chromium content migrates to slag and dust and becomes oxides. For example, ferrochrome is charged into a converter to produce stainless steel crude molten steel (high chromium molten steel before final decarburization), which is transferred to a ladle and blown with acid under vacuum to reduce the C to a predetermined value. In the process of obtaining stainless steel, 5 to 7 of the chromium content used in the slag generated in the converter and the slag and dust generated in the final decarburization process is
% will be transferred. In order to reduce the chromium content in slag, alloys such as Fe-Si are added to reduce and recover chromium oxide, but for example, expensive reducing agents are used before finishing decarburization. Reducing the molten metal has no effect other than recovering the chromium content from the slag (even if the molten metal is deoxidized, it will be oxidized again during final decarburization, so no effect will remain), so it cannot be said to be rational. . If there was a way to reduce and recover chromium by processing chromium-containing generated products at low cost,
Such an inefficient intermediate step of deoxidation can be omitted. In addition, if we try to increase the productivity of stainless steel manufacturing, we will inevitably increase the oxygen supply rate, and as a result, the chromium content in the slag after acid blowing and the amount of dust generated will also increase. . In addition to slag and dust generated during the steelmaking process, scale, grinding debris, and
Chromium is generated in the form of oxides, such as gas-cutting products and pickling sludge, but no efficient treatment method has been found so far. In other words, (i) Even if an attempt is made to reduce and recover the chromium content by treating slag, which has a relatively low chromium content of 10% or less, by itself, the slag/metal weight ratio produced is extremely high. It's too much to work as a process. (ii) There are examples of materials with a relatively high chromium content, such as dust, scale, and grinding chips, being molded and charged into a special electric furnace, and then reduced and recovered using carbon materials. However, in this case, there is a problem that both equipment costs and variable costs are high because expensive electric power is used and processing is performed on a small scale. Therefore, it is desirable to reduce and recover the chromium content of any generated material by effectively utilizing the characteristics of the generated material, using existing high chromium alloy manufacturing equipment such as stainless steel, and using inexpensive reducing agents and energy. As a result, it has been desired to develop a treatment method that can reduce the level of chromium content of the generated product to a significantly low level. The present invention was obtained as a result of various studies from the above-mentioned viewpoints, and the gist of the invention is to use a top-bottom blowing converter type melting reduction furnace, and to supply chromium raw material and carbonaceous material while bottom-blowing. While strongly stirring the acid bath, the carbonaceous material is suspended in the slag, and the carbonaceous material is combusted by blowing an oxidizing gas jet from an upper blowing lance to generate heat. In the process, which consists of the first smelting stage in which the chromium raw material is melted and reduced, and the second smelting stage in which the supply of the chromium raw material is stopped and the blowing acid and the bath are stirred, chromium oxide is removed during the production of stainless steel. The generated material containing chromium oxide is charged into a smelting reduction furnace together with the carbonaceous material, and the generated material containing chromium oxide during stainless steel manufacturing is used as a slag generation element, and the slag/metal weight ratio in the furnace is adjusted to 0.2 or more. A method for treating chromium oxide-containing waste produced during stainless steel production, characterized by reducing and recovering the chromium content of the chromium oxide-containing waste produced during stainless steel production. . Hereinafter, the present invention will be explained in detail with reference to specific examples. First, the case where it is used in the stainless steel manufacturing process will be described. When producing stainless steel in a top-bottom blowing converter, the amount of slag produced is usually at a slag/metal weight ratio of 0.15.
It is as follows. Under conventional steelmaking conditions, the more slag there is, the _more chromium loss to the slag. It is common sense to keep the amount to the minimum necessary by adding the necessary flux such as lime. In contrast, the present invention is based on the experimentally found results shown in FIG. The focus is on utilizing the phenomenon of increasing the reduction and recovery efficiency of chromium with carbon. In FIG. 1, the appropriate surrounding conditions are as follows. (i) Strong stirring is performed by bottom blowing gas. If stirring is insufficient, the reduction reaction of chromium oxide (chromium oxide added to the furnace and produced by reoxidation of molten metal with blowing acid) will be delayed, especially when the slag/metal weight ratio is As the value increases, the chromium content in the slag becomes higher than the curve shown in FIG. (ii) Free carbonaceous material coexists in the slag. Free carbonaceous materials, such as coke lumps, are active reaction sites for the reduction of chromium oxides in the slag, as well as the heat generated by partial oxidation. Note that when the slag/metal weight ratio is less than 0.3, the coexistence of free carbonaceous material means that the molten metal is inevitably carbon saturated, but when the amount of slag increases beyond that, free carbonaceous material coexists even under strong stirring. Since direct contact between the molten metal and the molten metal can be prevented, it is also possible to make the carbon in the molten metal unsaturated. Slag/metal weight ratio
Below 0.15, the chromium content in the slag is high even in the coexistence of free carbonaceous material, because the top-blown oxygen jet hits the molten metal surface and chromium reoxidation occurs simultaneously. When the amount of slag increases and the slag/metal weight ratio exceeds 0.2, reoxidation of the molten metal by the top-blown oxygen jet is prevented, so the chromium content in the slag stabilizes at a low level. An example of an operating method using the conditions for reducing the chromium content in slag shown in FIG. 1 is shown below. When producing stainless steel in a top-bottom blowing converter (especially in order to obtain molten metal for the subsequent finishing decarburization process),
(When performing raw material melting and primary decarburization), normal operation 2
The slag produced in one heat or more heats is treated in one heat operation under special conditions. Even if the slag produced by normal heat remains in the furnace, 1
It is also possible to remove the slag first and then return it. Dust, sludge, grinding chips, etc. are collected in appropriate amounts, formed into pellets or briquettes, and dried. It is advantageous to mix a carbonaceous material such as coke powder during molding in order to shorten the reduction reaction time. Stainless steel manufacturing under the above-mentioned special conditions means that ordinary stainless steel raw materials (hot metal, ferrochrome, scrap, lime, etc.) are combined with slag, molded products of generated products such as dust, grinding waste, and sludge, and charcoal such as coke. This refers to mixing and charging materials such that the slag/metal weight ratio is 0.2 or more. The amount of carbonaceous material such as coke is determined by the amount of carbon dissolved in the molten metal, the amount required to reduce chromium and iron oxides in the charged raw material, and the reduction reaction heat generated by combustion to CO or CO ₂ . The amount of sensible heat required due to the increase in the amount of refrigerant charged compared to normal operation is determined as the sum of the amount to be supplied by combustion to CO or CO ₂ . However, in reality, the ratio of CO and CO ₂ in the exhaust gas varies depending on the operating conditions of the reactor used, and the required amount of carbon materials such as coke changes accordingly. Blow acid from the top and bottom is used to generate heat while stirring strongly to reduce the chromium oxide to a predetermined value (the value is determined depending on how the slag discharged outside the system is used). Proceed until it becomes 0.5% or less. The chromium content of the slag can be controlled by the acid blowing time, temperature, etc. When T/Cr in the slag drops to a predetermined value, the furnace is tilted to discharge the slag. After most of the slag has been discharged, further acid blowing is carried out to reduce the carbon content of the molten metal to the level required from subsequent steps. In this way, in order to efficiently reduce chromium oxide in slag using the inexpensive means of blowing acid and coke, a larger amount of slag than conventional methods can be reduced.
The feature of this method is that it uses all the slag, dust, etc. generated during heat or higher heat. The above has described a method for reducing and recovering the chromium content by treating generated materials containing chromium oxide in the stainless steel manufacturing process, but this method can be applied to the ferrochrome manufacturing process. That is, carbon-containing semi-reduced chromium pellets produced from chromium ore or powdered chromium ore, carbonaceous material, and flux are charged into a top-bottom blowing converter type smelting reduction furnace, and blown acid is generated to generate heat due to C+O→CO or C+O ₂ +CO ₂ . When reducing chromium oxide using a reaction, the chromium oxide-containing generated product from the stainless steel manufacturing process, which is the object of the present invention, has the following advantages as a raw material. (i) Contains chromium oxide that should be reduced and recovered. (ii) CaO and SiO ₂ as accompanying substances can replace lime and silica added as slag forming agents in the ferrochrome melting and reduction process. The role of the slag agent added in the ferrochrome smelting reduction process is to change the composition of the MgO−Al ₂ O ₃ −SiO ₂ gangue in the chromium ore to make the viscosity and melting point of the produced slag suitable for smelting reduction. In order to reduce the ratio of harmful substances such as Al ₂ O ₃ to an acceptable level.
CaO, SiO2 _, etc. are added. On the other hand, the slag generated in the stainless steel manufacturing process
It is suitable as a flux because it contains large amounts of CaO and SiO ₂ and has a low content of harmful substances such as Al ₂ O ₃ , and it is said that it has a faster slag-forming effect than adding quicklime etc. It's also effective. (iii) When it is in the form of powder such as dust, grinding chips, sludge, etc. or in the form of sludge with moisture, it can be easily blended when producing carbon-containing chromium pellets from chromium ore powder. In this way, the products containing chromium oxide generated in the stainless steel manufacturing process are well suited as auxiliary raw materials in the ferrochrome melting and reduction process. In the ferrochrome smelting reduction process in a top-bottom blowing converter type smelting reduction furnace, chromium ore is
A large amount of slag with a slag/metal weight ratio of _0.3 or more is produced due to the presence of MgO, Al ₂ O ₃ C, and SiO.
By utilizing strong stirring by bottom blowing, addition of carbonaceous material, and efficient heat generation by top blowing, chromium oxide can be reduced and recovered to reduce the chromium content in the discharged slag to a low level of 1% or less. can be easily lowered to Example (1) When used in the stainless steel manufacturing process: The following raw materials are charged into a top-bottom blowing converter with a rating of 150 tons.

[Table] Top blown acid rate 3900Nm ³ /hr, bottom blown acid rate
Blow acid at 4000Nm ³ /hr for 60 minutes, metal component Cr:
17%, Fe: 77%, C: 5%, P: 0.040%,
S: 0.025%, metal temperature 1520℃ (metal amount
140t) metal, T・Cr: 0.5%, T・Fe:
When 42 tons of 0.3% slag (slag/metal = 0.34) was obtained, the furnace was tilted to remove 90% of the slag. Next, the steel was subjected to top and bottom acid blowing to bring the C content to 0.5% and the temperature to 1650°C, and then tapped into a ladle, and was subjected to acid blowing under vacuum to perform final decarburization to a C content of 0.04%. (2) When used in the ferrochrome manufacturing process: Using a top-bottom blowing converter (six bottom blowing tuyeres) with a rated molten metal amount of 100 tons, 60 tons of ferrochrome (Cr: 55%, Si: 0.1%, C: 8%) was dispensed approximately every 3 hours. Residual metal from previous heat
Add the following raw materials to 20t. (i) Semi-reduced pellets: Dust generated in the stainless steel manufacturing process (T・Cr: 25
%) 2, sludge (T・Cr: 18%) 2,
Coke powder is added to a mixture of grinding waste (T/Cr: 9%) in a ratio of 2 parts, formed into pellets, and the pellets (component: T/Cr :32
%, T・Fe: 19%, MgO: 11%, Al ₂ O ₃ : 12
%, CaO: 2%, SiO ₂ : 9%, chromium content preliminary reduction rate of 55%) was added in portions at a rate of 2 t/min over about 60 minutes. (ii) Carbon material: Coke (C content: 88%, particle size: 20-50
mm), almost in parallel with the semi-reduced chromium pellets mentioned above.
Inject 45 tons. (iii) Slag generated in the stainless steel manufacturing process: CaO: 58%, SiO ₂ : 20%, MgO: 9%,
Al ₂ O ₃ : 1%, T・Cr: 6%, T・Fe: 3%
The generated slag, which is divided into pieces of 50 mm or less, is charged in 13.5 tons from above the furnace in parallel with the semi-reduced chromium pellets. (iv) Lime: CaO content 97% (particle size 20-50 mm): 7.5 tons of this lime is added in portions in parallel with (iii). Blowing acid is top blowing 23000Nm ³ /hr for about 60 minutes, bottom blowing
Perform at 4500Nm ³ /hr. After adding the raw materials containing chromium, top blow 15000N for 30 minutes.
m ³ /hr, bottom blowing 4500Nm ³ /hr, additional 4t of coke is charged in installments for finish reduction, and the coke is returned to the furnace.
CaO: 26%, MgO: 24%, Al ₂ O ₃ : 23%,
SiO ₂ : 25%, T・Cr: 0.7%, T・Fe: 0.5
% of slag and 60 tons of ferrochrome are present (slag/metal weight ratio = 1.02), and then 2/3 of the bath water is discharged. As described above, the present invention takes advantage of the features of chromium-containing products generated in the stainless steel manufacturing process (relatively low chromium content and has a slag-making effect), and utilizes the features of the chromium-containing products generated in the stainless steel manufacturing process to create a top bottom used in the manufacturing of stainless steel, ferrochrome, etc. Using a blowing converter type reactor, the chromium content is reduced and recovered with high efficiency using inexpensive carbonaceous material, making it possible to reduce the chromium content of the generated product discharged outside the system to a significantly low level. It has great economic and industrial effects in terms of streamlining the stainless steel manufacturing process, improving the effective utilization rate of chromium resources, and protecting the environment.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the influence of the slag/metal weight ratio on the reduction and recovery of chromium in a top-bottom blowing converter.

Claims (1)

[Claims] 1 Using a top-bottom blown converter type smelting reduction furnace, while supplying the chromium raw material and carbonaceous material, the bottom-blown acid and the bath were strongly stirred, and the carbonaceous material was suspended in the slag. The first stage of smelting involves burning the carbonaceous material by blowing an oxidizing gas jet from the top blowing lance to generate heat and melting and reducing the chromium raw material.Then, the supply of the chromium raw material is stopped and the blowing acid is removed. In the second smelting process, which involves stirring the bath, the generated material containing chromium oxide during stainless steel production is charged into a smelting reduction furnace together with carbonaceous material, and the chromium oxide produced during stainless steel production is charged into a smelting reduction furnace. Using the contained generated material as a slag generation element, blowing acid while maintaining the slag/metal weight ratio in the furnace at 0.2 or more, reducing the chromium content of the generated material containing chromium oxide during the production of stainless steel, A method for treating chromium oxide-containing materials generated during stainless steel manufacturing, the method comprising recovering chromium oxide-containing materials.