JPS6249347B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing metals or alloys, particularly high chromium alloys such as ferrochrome, at low cost and with high yield by a smelting reduction method that does not depend on electric power.

Conventionally, high chromium alloys, such as ferrochrome containing 50% or more of Cr, have been produced by heating, melting, and reducing chromium ore or its semi-reduced product in an electric furnace. If this energy source can be replaced with primary energy that is cheaper than electricity (especially the combustion energy of coal-based solid carbon materials such as coal and coke, hereinafter referred to as solid carbon materials or carbon materials), it would be economically advantageous. Gender is huge.

In order to produce high chromium alloys using the combustion heat of carbonaceous materials without using electricity (this is called the smelting reduction method), (i) carbonaceous material oxidation conditions for efficient heat generation and chromium (ii) How to accelerate the reduction of chromium oxide, which is normally an extremely slow reaction, under conditions where the amount of slag produced is extremely large. However, a top-bottom blowing converter type is available as a reaction vessel method to solve this problem. Figure 1 shows an outline of the equipment. 1 is a rotary kiln used for heating and solid phase reduction of a mixture (such as pellets) of chromium ore powder and carbonaceous powder such as coke. 2 is a converter-like smelting reduction furnace that receives the pre-reduced pellets and melts them while reducing the remaining chromium and iron oxides. Tuyere 3 for blowing
(There may be more than one) and a lance 4 for blowing oxygen into the furnace from above. In the figure, 5 is a hood, 6 is a charcoal material, a hopper for lime, 7 is a molten metal, 8 is a molten slag, 9 is a chromium pellet, 10 is a carbon material, 11 is a bubble, 12 is a pellet supply amount adjustment tank, and 13 is a raw material. It is a supply amount control device.

The molten alloy is left in the furnace, and raw materials (semi-reduced chromium pellets, carbonaceous materials) are supplied from the rotary kiln, while blowing acid is applied to burn some of the carbonaceous materials, and the energy is used to convert the raw materials. Proceed with melting and reduction to increase the amount of molten alloy. In this case, a gas containing oxygen (for example, the tuyere is made of a double pipe, and the tuyere protective gas such as propane gas or Ar is supplied from the outer pipe, and oxygen gas is supplied from the inner pipe) into the molten metal from the bottom blowing tuyere 3. ), but the effects of this bottom blowing gas are: (i) Strongly stirring the metal and the generated slag layer to increase the reduction reaction rate of chromium oxide; (ii) Burning the carbon in the metal. The two methods are to heat the metal bath and maintain the metal at an appropriate temperature (20°C or more and 100°C or less higher than the freezing point). Regarding the latter, if there is no injection of oxygen-containing gas and there is a lot of slag, such as in ferrochrome smelting, the heat generated in the smelting reduction furnace will be caused by the oxygen supplied from the top blowing lance 4 in the slag. CO ₂ from carbonaceous materials or generated CO gas
Since heat is supplied to the metal through the slag, it is necessary to make the slag temperature higher than the metal temperature. This is undesirable because the high slag temperature increases the load on the refractories.

The oxygen supply from the top blowing lance 4 is for burning carbonaceous materials such as coke to generate heat, and is the main source of heat generation in this smelting method. In order to increase the smelting reaction rate, measures are taken to increase the combustion rate of the carbon material by top-blown oxygen, thereby increasing the heat generation rate.

The reason why the top-bottom blowing converter type is more suitable than other types is as follows.

(i) Without bottom blowing...The rate of chromium reduction in the slag is slow due to insufficient stirring. Furthermore, since the metal bath cannot be directly heated, the slag temperature becomes relatively high, which, together with the extension of the treatment time, places a significant load on the refractories.

(ii) In the case of only bottom blowing...The number of tuyeres for blowing multiple oxygen increases, making equipment management troublesome. In addition, since the combustion of carbonaceous materials must be carried out entirely through the oxidation of the metal phase components (in the case of carbon, the C dissolved in the metal), if the amount of slag increases, the dissolution of the carbonaceous materials into the molten metal will be delayed. , re-oxidation of the molten metal is likely to occur.

As mentioned above, the top-bottom blown converter type is the most advantageous furnace type in smelting reduction smelting of ferrochrome.
When operating semi-continuously as mentioned above,
The following two points are important.

(i) It is not preferable to raise the temperature of the molten alloy excessively in order to prevent damage to the refractories and bottom blowing tuyeres.

(ii) On the other hand, if the molten alloy temperature becomes too low (when a raw material containing chromium oxide is introduced, its temperature increases, melting and ring formation of the oxide occur, and as a result, the molten alloy temperature decreases). A problem arises in that the tuyere becomes clogged due to solidification of the molten alloy or the formation of chromium oxide (chromium oxidation is more likely to occur than decarburization when the temperature is low) near the blowing tuyere. If the bottom blowing tuyeres become clogged, this will have a significant negative impact on subsequent operations and must be avoided.

In order to satisfy the above two conditions, it is desirable to be able to detect the temperature of the molten alloy phase and use it as a guideline to control the feed rate of raw materials (chromium pellets, carbonaceous materials, etc.), the blowing acid rate, etc.

However, when a large amount of slag is produced, such as in ferrochrome smelting (gangue content in chromium ore, gangue content in carbonaceous materials such as coal and coke, and fluxes such as lime added to turn it into slag). Therefore, it is difficult to measure the temperature of the molten alloy phase using conventional methods (immersion thermocouples, optical pyrometers, etc.). Moreover, even if measurements can be made with an immersion thermocouple, it is not practical to carry out measurements many times in terms of cost.

The present invention was obtained as a result of various studies from the above-mentioned viewpoints, and its gist is to use a top-bottom blowing converter type melting ring furnace and to supply chromium raw material and carbonaceous material while bottom-blowing. In a process consisting of a first stage of smelting, in which the chromium raw material is melted and reduced by blowing acid, and a second stage of smelting, in which the supply of the chromium raw material is stopped and the blowing acid and bath are stirred, Continuously measure the pressure in the bottom blowing tuyere pipe, and using the correlation between the pressure in the bottom blowing tuyere pipe and the temperature of the molten alloy in the smelting reduction furnace, calculate the temperature of the molten alloy from the measured pressure value. Based on the estimation results, in the first stage of smelting, the supply rate of chromium raw material and/or the rate of blowing acid is controlled, and in the second stage of smelting, at least the blowing acid rate is controlled. A method of operating a smelting reduction furnace characterized by controlling the smelting reduction furnace.

Hereinafter, a detailed explanation will be given using specific examples.

The feature of the present invention is that, as shown in FIG. This means that a device is installed to detect the pressure of either active gas or hydrocarbon gas (used to inject active gas or hydrocarbon gas). 24 in the figure
is a pressure conversion element, 25 is a strain amplifier, 26
is a recorder, and 27 is a lead wire. This method makes it possible to continuously detect the pressure in the bottom blow tuyere pipe during the entire operating period.

FIG. 3 shows an example of pressure fluctuations in the bottom blowing tuyere pipe during melt reduction treatment. An increase in pressure means that the amount of deposits at the tip of the tuyere (called pine loom) increases and resistance increases, and a sudden drop in pressure means that pine loom decreases or disappears. means. If the former condition progresses, there is a risk of tuyere clogging, and if the latter condition progresses, the tuyere will not be protected by the pine room, causing abnormal melting of the tuyere and increasing the rate of wear, which is undesirable. These results are already known phenomena in steelmaking, but when processing high-carbon, high-chromium molten metal as in the present invention, there is a difference between the pressure and the temperature of the molten alloy phase, as shown in Figure 4. We found that there is a close correlation.

In Figure 4, the bottom blowing conditions for ferrochrome melting reduction are: tuyere (inner pipe diameter): 20 mm, blowing acid speed:
800Nm ³ /piece.

In the case of steelmaking, pressure fluctuations occur rapidly around the critical temperature (this is because the deposits are mainly metal), so it is difficult to obtain information other than the critical temperature from pressure fluctuations. On the other hand, when oxygen is bottom-blown into a high-carbon, high-chromium bath, the blown oxygen first oxidizes the chromium in the molten metal to form oxides, which are then reduced by the carbon in the molten alloy phase. The difference in speed between the two processes determines the amount of oxide deposited (this becomes deposits on the tuyere tip), that is, the pressure inside the bottom blowing tuyere tube. The amount of oxide produced is primarily determined by the amount of oxygen blown in, whereas the rate of reduction of the oxide by carbon in the molten alloy is primarily determined by the temperature of the molten alloy phase. This is because, unlike the steelmaking process, carbon in the molten alloy is maintained at a value close to the saturated value. Therefore, unlike the steelmaking process, a stable and clear relationship can be obtained between the pressure inside the bottom blowing tuyere pipe and the temperature of the molten alloy phase over a wide temperature range. In the present invention, such a relationship is utilized to control the melt reduction process. That is, each operating condition (i.e.
A relationship diagram as shown in Figure 4 is created according to the amount of blown acid and the chromium content in the molten alloy layer, and this is used to estimate the molten metal temperature from the pressure measurement results, and the molten alloy temperature is set. If it is too low than the range, melting reduction furnace 2
Either reduce the amount of semi-reduced chromium pellets charged into the tank, or increase the amount of top-blown acid.
If the molten alloy temperature is too high than the set value, perform the opposite operation. In order to control the amount of semi-reduced chromium pellets supplied to the smelting reduction furnace 2, for example, as shown in FIG. The cutting amount may be controlled by, for example, a raw material supply amount control device. By performing this operation, semi-reduced chromium pellets can be fed at the maximum speed without any problems such as blockage of the bottom blowing tuyeres, and at the same time damage to the smelting reduction furnace body and tuyeres can be minimized. becomes possible.

Example Rated molten metal amount (molten metal amount just before tapping) 50t top-bottom blowing converter (1 top-blowing lance, nozzle 7mmφ x 7
A double-tube structure with holes, 4 bottom blowing tuyeres, and an inner tube diameter of 20 mmφ, with O ₂ flowing through the inner tube and propane gas flowing through the outer tube as a protective gas) was used as the reaction vessel, and intermediate drainage was performed once. , 33 tons of the generated molten alloy is tapped out, and 17 tons remain, resulting in semi-continuous operation. The pressure inside the tubes of the bottom blowing tuyeres is measured using a measurement system as shown in Figure 2.The pressure in each inner tube of the four tuyeres is measured, and the average value is used as a guideline for furnace control.

Chromium ore, the main raw material for melt reduction, is mixed with coke and crushed, then granulated into pellets.
After drying, it was charged into a rotary kiln and pre-reduced and preheated using the high-temperature gas coming out of the melting reduction furnace as a heating source. Approximately 80% of the carbonaceous material supplied to the smelting reduction furnace
% is charged into the rotary kiln as exterior charcoal,
Improve the reduction rate of semi-reduced chromium pellets and preheat the carbon material to be fed to the smelting reduction furnace. As shown in FIG. 1, there is a raw material supply amount control device 13 located between the rotary kiln 1 and the smelting reduction furnace 2, and the amount of raw material supplied to the smelting reduction furnace can be controlled in accordance with the above-mentioned pressure measurement value. The average composition and temperature of the semi-reduced chromium pellets fed to the smelting reduction furnace are as follows: T.
Cr: 36%, T.Fe: 18%, chromium content reduction rate: 66
%, iron reduction rate: 92%, MgO: 10%, Al ₂ O ₃ : 10
%, SiO ₂ : 9%, temperature: approximately 1000°C.

First phase of smelting reduction smelting: Semi-reduced chromium pellets,
Charcoal and lime are charged. A portion of the carbonaceous material and lime are supplied from the hopper 6 (separately provided for the carbonaceous material and lime) shown in FIG. The acid blowing speed is upward blowing:
Keep constant at 13000Nm ³ /hr, bottom blow: 800Nm ³ /hr x 4. The charging rate of the pre-reduced pellets is adjusted so that the pressure in the tuyeres mentioned above is maintained between 5 and 8 kg/cm ² (corresponding to the molten alloy temperature in the range of 1580 to 1630° C.). Charge 32 tons of pellets and 3.5 tons of lime in 60 minutes. The Cr content in the slag at the end of this period was 7.5%.

Second stage of smelting reduction smelting: The supply of semi-reduced chromium pellets is stopped, only the carbonaceous material is charged into the smelting reduction furnace, and while the bottom blowing acid rate is kept constant, the pressure inside the tuyere is increased to 5 to 8 Kg/cm ² (The higher the top blown acid rate, the higher the molten alloy temperature, which in turn reduces the tuyere tip pressure. The relationship between pressure and molten metal temperature (Figure 4) varies depending on the equipment, operating conditions (e.g. diameter of bottom blowing tuyere, amount of bottom blowing acid, etc.), and reducing Cr% in slag for 15 minutes. . The final slag components are CaO19%, _SiO2 20%, MgO24
%, Al ₂ O ₃ 22%, T.Cr 0.9%, and T.Fe 0.7%.

Approximately 90% of the generated slag is then subjected to intermediate slag,
The operations of the first and second stages of melting reduction smelting described above are repeated. After that, 2/3 of the molten metal produced following the tap slag is tapped. After that, the same cycle is repeated. The components and temperature of the tapped metal are as follows. Cr: 53%, Fe: 37%, C: 8.5%, Si: 0.5
%, S: 0.015%, P: 0.035%, temperature 1650°C.

In addition, by conducting operations using the method of estimating the molten alloy temperature by pressure detection as in the present invention, the refractory unit consumption can be reduced compared to the case where this method is not used.
30% reduction, and the frequency of tuyere blockage problems was reduced to 1/5.

As described above, the present invention provides metals or alloys,
In particular, when smelting high chromium alloys such as ferrochrome, which is difficult to reduce and produces a large amount of slag, without relying on electricity, it provides a means for smooth operation. This method has great economic effects because it makes it possible to manufacture ferrochrome, which is the main alloy material of high chromium steels such as stainless steel, at low cost.

[Brief explanation of the drawing]

Figure 1 shows one of the facilities used to carry out the present invention.
An explanatory diagram showing an example, FIG. 2 is a feature of the present invention,
A diagram showing an example of a system diagram of a pressure measuring device in the bottom blowing tuyere pipe, Fig. 3 is a diagram showing an example of pressure fluctuation in the bottom blowing tuyere pipe during melting and reduction processing, and Fig. 4 shows an example of the pressure fluctuation in the bottom blowing tuyere pipe. It is a figure which shows an example of the relationship between the pressure in a mouth pipe, and the temperature of a molten alloy phase. 1: Rotary kiln, 2: Melting reduction furnace, 3:
Bottom blowing tuyere, 4: Lance, 5: Hood, 6: Charcoal material,
hopper for lime, 7: molten metal, 8: molten slag, 9: chrome pellets, 10: carbonaceous material, 11: bubbles, 12: pellet supply amount adjustment tank, 13: raw material supply control device, 21: bottom of smelting reduction furnace, 22 : Bottom blowing tuyere, 23: Inner pipe, 24: Pressure conversion element, 25:
Strain amplifier, 26: Recorder, 27: Lead wire.

Claims (1)

[Claims] 1 A first stage of smelting in which a top-bottom blown converter-type melting ring furnace is used to supply chromium raw materials and carbonaceous materials while bottom-blowing acid is performed to melt and reduce the chromium raw materials, and then the chromium raw materials are supplied. In the process consisting of the melting reduction process in the second stage of smelting, in which the blowing acid is stopped and the bath is stirred, the pressure inside the bottom blowing tuyere pipe is continuously measured, and the pressure inside the bottom blowing tuyere pipe and the melting reduction process are continuously measured. The temperature of the molten alloy is estimated from the measured value of the pressure using the correlation of the temperature of the molten alloy in the furnace, and based on the estimation result, the supply rate of the chromium raw material is determined in the first stage of smelting. and/or a method for operating a smelting reduction furnace, which comprises controlling at least the blowing acid rate in the second stage of smelting.