JPS5985841A - Manufacture of ferrochromium - Google Patents

Abstract

PURPOSE:To improve the rate of reduction to Cr and the yield of metal by controlling the amounts of a reducing agent and a slag making material to be additionally charged into a furnace and the volume of oxygen to be blown so as to make the temp. of slag and the amount of the reducing agent in the furnace close to set values for optimum operation. CONSTITUTION:Chrome ore is fed to a rotating furnace together with a reducing agent, a slag making material and oxygen, and melting and reduction are carried out. At this time, one or more among the temp. of slag in the furnace, the amount of the reducing agent in the furnace and the surface temp. of the refractories are measured, and at least one among the amount of a reducing agent to be additionally charged, the amount of a slag making material to be additionally charged, the volume of oxygen to be blown, the position of an oxygen blowing lance and the speed of rotation of the furnace is controlled so as to make said measured values close to set values required to carry out optimum operation. Thus, the rate of reduction to Cr and the yield of metal are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ferrochrome using a batch method in which ferrochrome is produced by smelting and reducing chromium ore + m using a rotary furnace.

Conventionally, ferrochrome was produced by charging chromium ore into an electric furnace together with a reducing agent such as coke and a slag-forming agent such as limestone and refining it in an electric furnace, which resulted in the consumption of a large amount of electricity for refining. This was considered a serious problem from the viewpoint of resource conservation and economic efficiency.

The present inventors have conducted extensive research to solve the above-mentioned problems and develop a method for producing ferrochrome that can replace the conventional electric furnace smelting process. He invented a method to do this and filed a patent application (Japanese Patent Application No. 112936/1982).

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 chromium ore is melted by blowing oxygen or oxygen-enriched air into it. At the same time, the high-temperature exhaust gas discharged from the rotary furnace is all introduced into the rotary kiln, and the chromium ore to be supplied to the rotary furnace is preheated within the rotary kiln. According to this method, a large amount of chromium ore is Ferrochrome can be produced economically without consuming expensive electricity.

However, when implementing the above-mentioned method in a batch system, it was found that the following problems occurred during the refining process in a rotary furnace in actual operation.

(1) Chromium reduction rate and metal recovery rate If the slag temperature is below 1650°C, the chromium reduction reaction will be delayed and the reduction rate will be as low as 80-90%.9 As a result, the metal recovery rate and metal recovery rate will be low. The variation in the chromium content inside is a major factor.

In addition, the amount of in-furnace reducing agent in the rotary furnace is 5
When the temperature becomes less than 0, the atmosphere in the furnace becomes weakly reducing due to the excessive amount of oxygen blown into the furnace, and the metal is reoxidized, resulting in a decrease in both the chromium reduction rate and the metal recovery rate.

(P contained in the metal due to excessive combustion of the reducing agent in the furnace)
The amount is as high as 0.06-0.07%.

Furthermore, since the slag composition shifts to the low basicity side, the amount contained in the metal becomes as large as 0.8% and 0.2%. As a result, problems arise when the product (ferrochrome) is used for the production of high-grade steel.

(3) If the difference between the surface temperature of the large lining of the rotary furnace and the slag temperature becomes large during the reduction period of the refractory melting and the separation stage of the metal and slag, the refractory will suffer severe melting loss. Furthermore, since the MPO saturation value of the slag composition at the time of melting (10 to 20% in CMFO) and the final slag composition at the end of refining (Mjl [O + 20 to 30%) is different, the erosion of the refractory is severe. This results in increased wear and tear on the refractories.

(4) Amount of oxygen blown The slag temperature is mainly affected by the amount of oxygen blown.
If the amount of reducing agent in the furnace is not appropriate due to difficulty in ascertaining the amount, the amount of oxygen blown into the furnace is increased more than necessary in an attempt to raise the slag temperature, resulting in a weakly reducing atmosphere inside the furnace. This results in a decrease in the chromium reduction rate.

The present inventors have conducted extensive research in order to solve the above-mentioned problems. As a result, it was found that the major factors that cause the above-mentioned problems are the slag temperature, the difference between the refractory surface temperature and the slag temperature, the slag composition, the amount of reducing agent, and the composition of the exhaust gas. It has been found that the above problem can be solved if controlled in this manner.

(1) Slag temperature control If the slag temperature rises rapidly, the melting loss of refractories will be reduced. On the other hand, if the slag lagoonality decreases, the dissolution reduction action will be delayed and the chromium reduction rate will decrease. Therefore, in order to prevent sudden increases or decreases in slag temperature, the amount of reducing agent in the furnace, composition of exhaust gas, slag temperature, and refractory surface temperature are accurately grasped, and the required oxygen injection is determined through calculation processing. If the slag temperature is maintained at an appropriate level by determining the amount of slag and controlling the injection amount, and controlling the additional charging amount and charging speed of the slag-forming agent and reducing agent, the chromium reduction rate can be improved and refractories can be improved. It is possible to reduce erosion loss. FIG. 1 is a diagram showing an example of the relationship between the appropriate slag temperature controlled as described above and the chromium reduction rate.

(2) Refractory surface temperature control When the surface temperature of the refractory lining of the rotary furnace becomes higher than the refining temperature required for melting and reduction, the amount of erosion of the refractory increases; If it is low, the solubility of the raw material will deteriorate and the chromium reduction rate will decrease. Therefore, an appropriate amount of in-furnace reducing agent is determined from the exhaust gas composition and oxygen injection amount, and the in-furnace reducing agent is controlled to be the appropriate amount, and
If the amount of oxygen blown into the furnace is controlled to create a stable reducing atmosphere inside the furnace, the range of fluctuation in slag temperature will be small, the difference between the refractory temperature and slag temperature will be maintained within an appropriate range, and chromium reduction will be achieved. It is possible to improve the efficiency and reduce the erosion of refractories. FIG. 2 is a diagram showing an example of the relationship between the slag temperature and the difference between the appropriate refractory surface temperature controlled as described above and the slag temperature.

(3) Slag composition control When the temperature of slag increases, the composition changes, and as a result, the amount of erosion of refractories increases. Therefore, based on the slag temperature, the initial composition of raw materials, the amount of reducing agent burned and consumed in the furnace, and the amount of additional slag forming agent, it is determined that the additional charging of slag forming agent is appropriate in order to obtain an appropriate slag composition. By determining the amount, adding the slag forming agent to the appropriate amount, and controlling the addition rate, the slag temperature can be controlled and an appropriate slag composition can be obtained, reducing the erosion of refractories. can. FIG. 3 is a diagram showing an example of the relationship between the appropriate slag composition controlled as described above and the slag temperature.

(4) Control of the amount of reducing agent in the furnace If the amount of reducing agent in the furnace is insufficient, the inside of the rotary furnace becomes a weakly reducing atmosphere, resulting in a decrease in the chromium reduction rate and metal recovery rate. Therefore, by determining the appropriate amount of reducing agent in the furnace from the exhaust gas composition, oxygen injection amount, and reducing agent charging amount, and determining the additional reducing agent charging amount to reach the above-mentioned appropriate amount, the chromium reduction rate and metal recovery rate can be increased. FIG. 4 is a diagram showing an example of the relationship between the appropriate amount of in-furnace reducing agent controlled as described above and the chromium reduction rate.

(5) Composition control of exhaust gas If the amount of 02% in the exhaust gas during the melting period is high, the efficiency of oxygen use in the furnace will decrease. Further, the state of the atmosphere inside the furnace can be determined from the composition of the exhaust gas, and if the inside of the furnace is in a low reducing atmosphere during the reduction period, the generated metal will be reoxidized. Therefore, during the melting stage, it is possible to increase the efficiency of oxygen use by detecting the composition of the exhaust gas and controlling the amount of oxygen blown from the raw material temperature, refractory surface temperature, and exhaust gas composition so that it is at an appropriate value. can. Furthermore, during the reduction period, the slag can be kept at a temperature within an appropriate range by maintaining the reducing agent in the furnace at an appropriate amount so that the exhaust gas composition is at an appropriate value, and by controlling the amount of oxygen blown into the furnace. FIG. 5 is a diagram showing an example of the relationship between the properly controlled exhaust gas composition and slag temperature as described above.

This invention was made based on the above findings, and involves supplying chromium ore together with a reducing agent and a slag-forming agent into a rotary furnace whose axis is horizontal or gently inclined, and blowing oxygen into the rotary furnace. In the method for producing ferrochrome in which ferrochrome is produced by melting and reducing chromium ore, at least one of the slag temperature, the amount of reducing agent in the furnace, and the refractory surface temperature in the rotary furnace is measured, and the measured value is determined to be The additional charging amount of reducing agent, the production This method is characterized by controlling at least one of the additional charging amount of sludge agent, the amount of oxygen blown in, the position of the oxygen blown lance, and the rotational speed of the furnace body.

Next, an example of a control system for implementing the present invention will be explained based on the system diagram shown in FIG. As shown in Figure 6, the in-furnace measuring instruments include a slag immersion continuous thermometer, a slag immersion batch thermometer, a thermometer embedded in the furnace wall, a radiation thermometer on the surface of the furnace wall, a furnace wall heat flow meter, and an exhaust gas analyzer. These instruments measure the slag temperature, refractory surface temperature, exhaust gas composition, and furnace wall heat addition.

As equipment instruments for operation, we use an oxygen flow meter, lance position measuring meter, raw material charging amount recorder, and furnace body rotation speed meter. Measure the charging amount (slag agent, etc.), furnace rotation speed, and lance position.

In addition, as initial operating conditions, the initial blending amount of raw materials, furnace body temperature, raw material preheating temperature, etc. are ascertained.

The amount of reducing agent in the furnace was determined from the difference between the amount of reducing agent consumed and the amount of reducing agent charged, which were calculated from the slag temperature measurement, refractory surface temperature measurement, oxygen flow rate, and exhaust gas composition obtained above. A computer calculates the difference between at least one set value and a set value for optimal operation, and various control devices are used to adjust the oxygen flow rate,
It controls at least one of the position of the oxygen injection lance, the rotational speed of the furnace body, the amount of additional reducing agent charged, the amount of fuel for keeping the rotary furnace warm, the amount of additional slag forming agent charged, etc.

Next, the control means by the above-mentioned control system will be explained.

+I+ Control to increase the chromium reduction rate From the measured value by at least one of a slag immersion continuous type thermometer, a slag immersion batch type thermometer, a thermometer embedded in the furnace wall, a furnace wall surface radiation type thermometer, and a furnace wall heat flow meter The slag temperature is known directly or indirectly, and the reducing agent consumption in the furnace is calculated from the oxygen flow rate measured by an oxygen flow meter or oxygen integrated flow meter and the exhaust gas composition measured by an exhaust gas analyzer. The amount of reducing agent in the furnace is determined from the difference between the amount of reducing agent and the amount of reducing agent charged. At least one of the additional charging amount of the reducing agent, the oxygen injection amount, the oxygen injection lance position, and the furnace body rotation speed is controlled so that the amount of the oxygen injection is maintained.

(2) Control to minimize erosion of refractories (al
Slag immersion continuous thermometer, slag immersion batch thermometer,
The slag temperature is directly or indirectly known from the measurement value of at least one of a thermometer embedded in the furnace wall and a radiation type thermometer on the surface of the furnace wall, and the appropriate slag composition estimated from the slag temperature and the actual amount of raw material charged are used to determine the slag temperature. Additional slag forming agent is charged into the furnace so that the difference with the calculated slag composition in the furnace is minimized.
This controls the slag composition.

(bl) The slag temperature is measured by a slag immersion continuous thermometer or a slag immersion batch thermometer, and at least one of a thermometer embedded in the furnace wall, a radiation thermometer on the surface of the furnace wall, and a furnace body heat flow meter is used to measure the slag temperature. The internal refractory surface temperature is measured, and at least one of the oxygen injection amount, oxygen injection lance position, and furnace rotation speed is measured so that the difference between the slag temperature and the refractory surface temperature is within a preset appropriate range. The difference between the refractory surface temperature and the slag temperature is thereby maintained at an appropriate level.

+31 Controlled slag immersion continuous thermometer, slag immersion batch thermometer to minimize oxygen injection amount and reducing agent charge amount,
The slag temperature is directly or indirectly known from the measurement value by at least one of a thermometer embedded in the furnace wall, a radiation type thermometer on the surface of the furnace wall, and a furnace wall heat flow meter, and the 02 flow rate measured by an oxygen flow meter or an oxygen integrated flow meter The amount of reducing agent in the furnace is determined from the difference between the amount of reducing agent consumed in the furnace and the amount of reducing agent charged, which is calculated from the amount of reducing agent consumed in the furnace and the exhaust gas composition measured by the exhaust gas analyzer. The additional charging amount of the reducing agent, so that the amount of the reducing agent becomes the slag temperature and the amount of the reducing agent in the furnace to obtain the preset appropriate slag temperature, amount of reducing agent in the furnace, and exhaust gas composition. At least one of the oxygen injection amount, the oxygen injection lance position, and the furnace rotation speed is controlled.

The above-mentioned control makes it possible to maintain the exhaust gas composition and the amount of reducing agent in the furnace at appropriate values by controlling the amount of oxygen blown in and the amount of additional reducing agent charged during the melting period. In this process, the slag temperature, the difference between the refractory surface temperature and the slag temperature, and the slag composition can be maintained at appropriate values by controlling the amount of reducing agent in the furnace, the additional charging amount of slag-forming agent, and the amount of oxygen injection. I can do it. Furthermore, during the metal and slag separation stage, the slag temperature and
The difference between the refractory surface temperature and the slag temperature can be maintained at an appropriate value, and the metal and slag can be separated appropriately to improve the metal recovery rate. FIG. 7 is a diagram showing an example of the flow of controlling the amount of reducing agent (coke) in the furnace, and FIG. 8 is a diagram showing an example of the flow of controlling the amount of oxygen blown.

Next, the present invention will be explained based on examples.

High carbon Manufactured ferrochrome.

The rotary furnace has a raw material charging port at one end of the furnace body, and a water-cooled lance for oxygen injection is provided in the furnace through the charging port so as to be freely retractable. The rotary furnace is equipped with various sensors such as a furnace inner wall surface radiation thermometer, a slag immersion continuous thermometer, and an exhaust gas analyzer as measurement instruments, and an oxygen flowmeter and a lance position measuring instrument as operational equipment instruments. , a raw material charging amount recorder, a furnace body rotation speed meter, and a furnace body inclinometer. Furthermore, a computer is provided for inputting data from each of the sensors and the meter, and comparing and processing the data with appropriate values, and from the calculation processing results of the computer, the amount of reducing agent, slag temperature, refractory material, etc. It is equipped with an oxygen flow rate adjustment device, a lance position adjustment device, a reducing agent additional charge amount adjustment device, and a slag forming agent additional charge amount adjustment device for controlling the surface temperature and slag composition within appropriate ranges.

After the raw materials shown in Table 1 below were supplied to the rotary furnace having the above-mentioned apparatus, oxygen was started to be sprayed from the lance toward the raw materials in the rotary furnace in the direction shown in Table 1.

The amount of oxygen blown during the melting stage is 1, INi/-, and the composition of the generated exhaust gas is input into a computer and a correction process is calculated to minimize the amount of excess oxygen in the exhaust gas composition in order to improve the oxygen injection efficiency. Maximum], 'a 4 Nn? / of oxygen was blown into the furnace. 12 minutes after the start of refining coke as an additional reducing agent. ．． 5 and 9, and calculate the amount of combustion reducing agent sequentially from the exhaust gas composition and the amount of oxygen blown, and add additional reducing agent so that the amount of reducing agent in the furnace is maintained at 20 to 30 kg. The input amount was controlled. From the start of refining 2
After 0 minutes, the raw materials in the furnace began to form soft f-he, then passed through briquette f-h and melted off after 29 minutes.

During the reduction period, data such as exhaust gas composition, slag temperature, refractory surface temperature, oxygen flow rate, slag composition, etc. are input into the computer and correction processing is calculated to control the slag composition, slag temperature, and refractory surface temperature. , the reducing agent or slag-forming agent is charged at approximately 1.0 to 1.5 chest/rail, and the amount of oxygen blown is approximately 0.
．． 7~0, 9 Nrr? / While changing to win,
While maintaining the inside of the furnace in a reducing atmosphere, the slag temperature and the difference between the refractory surface temperature and the slag temperature were controlled to be maintained within appropriate ranges.

During the metal and slag separation period, the data on the exhaust gas composition, slag temperature, and refractory surface temperature are input into a computer and a correction process is performed to adjust the slag temperature to approximately 1700°C and to calculate the difference between the refractory surface temperature and slag temperature. In order to maintain the appropriate range of 140 to 160°C, the amount of oxygen blown is 0.6 to 0.
7 Nrr? /rM.

Refining was completed and hot water was tapped 60 minutes after the start of oxygen blowing. A skimmer was provided at the sprue during tapping, and a portion of the excess reducing agent and slag-forming agent were left in the furnace and used for circulation.

The obtained metal (high carbon ferrochrome) is 14.4Kf
, the slag has a weight of 24.2 Kp, and its composition is shown in Table 2.

Table 2, Figure 9 shows the above-mentioned refining process as a graph, and Table 2, Figure 10, shows the slag temperature and the difference between the refractory surface temperature and the slag temperature when refining using the method described above. A comparison is shown with a conventional method without control.

Table 3 also shows the metal composition, chromium reduction rate, metal recovery rate, amount of reducing agent charged, amount of oxygen blown, and amount of refractory erosion when 10 charges were performed using the method described above. A comparison is shown with a conventional method that does not perform extensive control.

From Table 3, if ferrochrome is produced by the method of the present invention, both the chromium reduction rate and the metal recovery rate are high;
It can be seen that the amount of reducing agent charged, the amount of oxygen blown, and the amount of refractory erosion are all low.

As described above, when 7Erochrome is produced by the method of the present invention, the following excellent effects can be obtained.

(1) Since the amount of reducing agent in the furnace, the slag temperature, and the reducing atmosphere in the furnace can be controlled to be appropriate, there is little variation in metal composition, and the chromium reduction rate and metal recovery rate can be stably improved.

(21) Since the slag temperature can be controlled within an appropriate range, the amount of reducing agent consumed in the furnace can be minimized, and since the slag composition can be controlled, it is possible to reduce the amounts of Pi and S in the metal.

(3) Since the slag temperature and the difference between the refractory surface temperature and the slag temperature can be controlled within appropriate ranges, and the syslag composition can be controlled by adding an appropriate amount of slag-forming agent, the amount of erosion of the refractory can be reduced. can be the lowest.

(4) Since the amount of reducing agent in the furnace can be accurately determined, it is possible to control the slag temperature and the atmosphere in the furnace with the minimum necessary oxygen injection amount, making it possible to reduce the amount of oxygen used. .

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of the relationship between appropriate slag temperature and chromium reduction rate, Figure 2 is a diagram showing an example of the relationship between the difference between the appropriate refractory surface temperature and slag temperature, and slag temperature, Third
Figure 4 shows an example of the relationship between the appropriate slag composition and slag temperature, Figure 4 shows an example of the relationship between the appropriate amount of reducing agent in the furnace and chromium reduction rate, and Figure 5 shows the relationship between the appropriate exhaust gas composition. Fig. 6 is a block diagram showing an example of a control system for carrying out the present invention, and Fig. 7 shows an example of the control flow for the amount of reducing agent (coke) in the furnace. FIG. 8 is a block diagram showing an example of the control flow of the amount of oxygen blown, FIG. 9 is a graph showing an example of the refining progress according to the present invention, and FIG. 10 is the slag temperature when refining according to the present invention. and is a graph showing the difference between the refractory surface temperature and the slag temperature in comparison with a conventional method. 21- (%) Continuous shooting sub-V mouth O (1) Drunkenness, ctc=Y Figure 3 2 Opening (minutes) Iomizu Figure 4 Time (minutes)

Claims (1)

[Claims] (1) 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 the chromium ore is melted and reduced by blowing oxygen into the rotary furnace. In the method for producing ferrochrome, in which at least one of the slag temperature, the amount of reducing agent in the furnace, and the refractory surface temperature in the rotary furnace is measured, and the measurement value is set to perform a predetermined optimal operation. The method is characterized by controlling at least one of the additional charging amount of the reducing agent, the additional charging amount of the sludge forming agent, the oxygen injection amount, the oxygen injection lance position, and the furnace body rotation speed so that the A method for producing ferrochrome. (2) The set values for performing the optimum operation are the slag temperature and the amount of reducing agent in the furnace to obtain a high reduction rate of chromium. The method for producing ferrochrome according to (3) the set value for optimal operation is a slag composition for minimizing melting loss of refractories. The method for producing ferrochrome according to item 11. (4) The set value for performing the optimum operation is a difference between a refractory surface temperature and a slag temperature to minimize melting loss of the refractory. Claim No. (11)
The method for producing ferrochrome as described in section. (5) The set values for performing the optimum operation are the slag temperature and the amount of reducing agent in the furnace to minimize the amount of oxygen blown and the amount of reducing agent charged. The method for producing ferrochrome according to item (1).