JP2014051428A - Carburization raw material and amorphous refractory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively use used carbon-containing unburned brick.SOLUTION: A new raw material which compares favourably with conventional raw materials, i.e. a carburization raw material is obtained by pulverizing a used carbon-containing unburned brick and firing it under conditions of an oxygen concentration of 5.0 to 9.0% and a temperature of 800 to 1000°C. Further a variety of amorphous refractories are manufactured by using the carburization raw material.

Description

  The present invention relates to a carburized raw material produced using carbon-containing unfired waste brick generated in a steelmaking factory or the like, and an amorphous refractory using the same.

BOF steelmaking plant, AOD furnace, RH furnace, an electric furnace, a lining refractories ladle etc., MgO-C _bricks, Al ₂ O 3 -MgO-C _bricks, Al _{2 O} 3 -C various such bricks Carbon-containing unfired brick is used.

Hereinafter, MgO—C brick as an example of carbon-containing unfired brick will be described.
MgO-C bricks have excellent corrosion resistance and spall resistance due to the high corrosion resistance of magnesia, the characteristics of carbon that do not easily get wet with slag, and high thermal conductivity, and are widely used as lining materials for steelmaking. ing.

  As raw materials used for this MgO-C brick, electrofused magnesia, seawater magnesia and the like are generally used as a magnesia source, and scaly graphite, earthy graphite and the like are generally used as a carbon source. Since the magnesia raw material is required to have corrosion resistance, the magnesia content is 95% by mass or more.

  The MgO-C brick is used for a certain period of time as a steelmaking lining furnace material, and then replaced with a new one. At that time, a large amount of used MgO-C brick is generated. Used bricks contain impurities generated during operation mainly on the operating surface side, so when reused as raw materials for MgO-C bricks as they are, the equivalent brick performance cannot be obtained. Recycling did not go much.

  For this reason, when recycling used MgO-C bricks, many of them have been reground and used for slagging materials, or sized and used as an irregular repair material. (For example, refer to Patent Document 1). Most of them are buried at disposal sites. In addition, since a large amount of money is required for burying disposal, further expansion of the amount of recycling has been an issue.

  When used MgO-C brick is blended as a raw material for an amorphous refractory without pretreatment, there is a problem that the molten metal boils because of metallic aluminum and carbon added as an antioxidant.

  On the other hand, Patent Document 2 discloses a method of adding a recycled raw material obtained by removing an altered layer on the working surface side of MgO-C brick after use and pulverizing the remaining part to MgO-C brick.

  JP 2011-121798 A   JP-A-8-319154

  An object of the present invention is to make effective use of carbon-containing unfired bricks, and that the obtained recycled material exhibits performance equal to or higher than that of conventional materials. Furthermore, the amorphous refractory using the recycled material exhibits characteristics such as workability, sinterability and corrosion resistance comparable to conventional products.

  That is, the present invention is a recycled raw material (hereinafter referred to as carburized magnesia raw material) obtained by oxidizing and separating magnesia and carbon by pulverizing, sizing and firing used MgO-C bricks. It is an amorphous refractory containing other raw materials.

  As a result of intensive research to solve the above problems, the present inventor separated carbon and magnesia by pulverizing used MgO-C bricks to 10 mm or less and performing an oxidation firing treatment, and impurities were It has been found that a carburized magnesia raw material having few and new excellent properties can be obtained.

  The carburized magnesia raw material is obtained by subjecting used MgO-C bricks to coarse crushing and sieving to a size of 10 mm or less. It is obtained by partially separating and removing carbon from used MgO-C brick. By the treatment based on the present invention, a raw material obtained by carburizing 0.5 to 7.0% by mass of carbon in magnesia is obtained.

  Carbon carburized in magnesia is exposed to high-temperature operation during operation of steelmaking facilities, and carbon is carburized in magnesia raw material. The amount of carburization varies in the range of about 0.5 to 7.0% by mass. The amount of carburization is an analysis value of only the clinker portion of the recycled raw material, and does not include free carbon.

According to the present invention, it is possible to effectively use used MgO-C brick as a raw material for carburized magnesia raw material. Therefore, the range of recycling can be expanded and the amount of burial processing can be reduced.
The same can be said for Al ₂ O ₃ —MgO—C brick and Al ₂ O ₃ —C brick.

It is the graph which showed the oxygen concentration in a rotary kiln as a parameter about the relationship between the processing temperature and the carbon amount of a carburized magnesia raw material when the grind | pulverization particle size of a used MgO-C brick raw material is 10 mm or less. It is a SEM photograph which shows the microstructure of a magnesia raw material. FIG. 2 (a) is a carburized magnesia raw material obtained according to the present invention, and FIG. 2 (b) is an untreated used MgO-C brick.

  When the used MgO-C brick is reused as a magnesia source, it is in a mixed state in which different kinds of raw materials are mixed only by crushing and sizing. We focused on the fact that free carbon and impurities can be removed by heat oxidation treatment to obtain a carburized magnesia raw material with high purity.

  First, a regeneration process for obtaining a carburized magnesia raw material from used MgO-C brick will be described.

  Used MgO-C bricks were obtained after using the converter. As a pretreatment, sorting of used MgO-C bricks was performed. This is because most of the obtained post-use MgO-C bricks contain things other than MgO-C bricks such as magnesia bricks and amorphous refractories used for the backing.

  After the used MgO-C brick is removed of deposits on the working surface side, it is coarsely pulverized with a jaw crusher, a roll crusher or the like, and sized to a particle size of 10 mm or less, and then fired. Fine particles may be included. When the particle size is 10 mm or more, the carbon inside the raw material tends to remain, and the oxidation baking treatment does not work well. From the viewpoint of recycling and using the MgO-C brick after regeneration, it is more preferable to perform a baking treatment at 5 mm or less.

  The used MgO-C brick applied to the present invention is not particularly limited as long as it is usually used in a converter, an electric furnace for steel making, a ladle or the like. Even if the MgO content and the carbon content in the used MgO-C brick vary, there is no need for separation or limitation. This is because it can be dealt with by controlling the oxygen concentration, processing temperature, input amount, residence time, and the like.

The equipment used in the firing process may be a single kiln, shuttle kiln, electric furnace, rotary kiln, etc. However, it is desirable to use a rotary kiln in consideration of fuel consumption, oxidation process in the firing process, and mass processing.
The firing zone temperature of the rotary kiln is desirably in the range of 800 to 1000 ° C. If the temperature is too low, oxidation firing does not proceed well even if the particle size and oxygen concentration in the furnace are adjusted. If the temperature is too high, fuel consumption will be reduced and it will be uneconomical.

  An example of operation of a rotary kiln facility used for oxidation firing will be described.

  A rotary kiln having an inner diameter of 1 m and a total length of about 5 m is prepared. An amorphous refractory is lined inside the kiln so that the inner diameter of the kiln is 600 mm, and a stirring lifter is installed inside the kiln. Oxidation firing proceeds effectively by attaching a lifter for stirring.

A dust collector will be installed on the kiln bottom side of the rotary kiln. Impurities contained in the fine powder part because the heat generated in the hot stove is pulled to the bottom of the kiln, extending the effective distance in the oxidizable calcination zone temperature range 800-1000 ° C, and at the same time carbon and organic melted material are burned out by oxidization SiO ₂ , Al ₂ O ₃ , CaO and the like are preferentially collected.

  A hot stove was installed on the rotary kiln feedstock discharge side, and recycled oil was used as the fuel. The amount of recycled oil used during combustion is about 20 to 40 l / hr.

  Further, since it is necessary to maintain the oxygen concentration in the rotary kiln at 5.0 to 9.0% by volume, air is driven. If the oxygen concentration in the furnace is lower than 5% by volume, the oxidation does not proceed due to the lack of oxygen that reacts with carbon. If the oxygen concentration is higher than 9% by volume, the introduced air causes a temperature drop, and 800 ° C. cannot be maintained, which is inappropriate. Oxygen can be used instead of air, but it is expensive and not economical.

  The raw material supply amount is adjusted so that the raw material filling rate in the kiln is 15% by volume or less. If the raw material filling rate is too high, a large amount of oxygen is required for the oxidation reaction in the kiln, so that it is necessary to increase the amount of air input, and it becomes difficult to maintain the temperature. It is necessary to drive air to such an extent that the firing temperature in the kiln is maintained at 800 to 1000 ° C. If it is driven too much, the temperature in the kiln is lowered and oxidation may not proceed.

  The rotation speed of the kiln is adjusted within a range of 3.0 rpm or less. If the rotational speed of the kiln is too high, the oxidation reaction of carbon will not proceed easily. This is because if the kiln rotation speed is high, the residence time in the oxidizable firing zone temperature range 800 to 1000 ° C. is shortened.

  The contents described above vary depending on the inner diameter, the overall length, the inclination, the rotational speed of the rotary kiln and the capacity of the hot stove and can be adjusted.

  Hereinafter, the present invention will be described in detail with reference to examples.

  FIG. 1 shows the relationship between the treatment temperature of the used MgO-C brick obtained in the experiment and the remaining amount of carbon with the oxygen concentration as a parameter.

  The amount of carbon in the graph shown in FIG. 1 is the total amount of free carbon and carbon carburized in the magnesia raw material. The amount of carbon in the good oxidation range of FIG.

  As shown in FIG. 1, the amount of carbon remaining in the raw material after oxidation and firing largely depends on the processing temperature of the rotary kiln and the oxygen concentration in the furnace. When the treatment temperature is lower than 800 ° C., the oxidation of carbon does not proceed. If it is higher than 1000 ° C., the oxidation of carbon proceeds, but the fuel efficiency is poor and it is not economical. If the oxygen concentration in the furnace is lower than 5% by volume, the oxidation does not proceed due to the lack of oxygen that reacts with carbon. If the oxygen concentration is higher than 9% by volume, the introduced air causes a temperature drop, and 800 ° C. cannot be maintained, which is inappropriate. Therefore, the area surrounded by a circle in FIG. 1 is an area where free carbon is oxidized and removed, and the amount of carbon is only carburized magnesia.

Table 1 shows examples and comparative examples in which the used MgO-C brick raw material was treated with a particle size of 10 mm or less and the temperature and atmosphere of the rotary kiln were changed.
The case where the amount of carbon of the obtained carburized magnesia raw material was 7% by mass or less was evaluated as good (◯), and the case where the amount of carbon was more than that was evaluated as defective (×). This is because the unoxidized carbon remaining in the raw material having a carbon amount of 7% by mass or more is discharged from the rotary kiln.

  Table 2 shows the used MgO-C brick used in the method of the present invention and the chemical components and physical properties of the carburized magnesia raw material obtained by the method of the present invention.

Carburized magnesia raw material tends to contain impurities SiO ₂ , Al ₂ O ₃ , and CaO on the side of 1 mm or less by classifying them to 5 to 1 mm or 1 mm or less, and only 5 to 1 mm is used for recycled refractories. For example, a refractory with higher corrosion resistance is obtained.

Photomicrographs of the carburized magnesia raw material and the untreated raw material are shown in FIG. As for the carburized magnesia raw material, carbon is carburized in the electrofused magnesia crystal, and it becomes a black crystal. Untreated raw materials are rich in carbon and impurities such as SiO ₂ , Al ₂ O ₃ , and CaO. Since the organic binder remains, the porosity is higher than that of the carburized magnesia raw material.

  Next, the carburized raw material produced in Example 1 was evaluated.

<Electric furnace stamp material>
Table 3 shows the configurations and evaluation results of the electric furnace stamp materials according to the examples and comparative examples of the present invention.

  In Table 3, the experiment No. 2-1 is obtained by substituting a part of the used magnesia raw material with the carburized raw material of the present invention for the conventional stamp material of 2-3. Similarly, Experiment No. 2-2 is obtained by substituting a part of the magnesia raw material used for the conventional stamp material of 2-4 with the carburized raw material of the present invention.

  A comparative experiment shown in Table 3 was conducted using raw materials having chemical compositions and physical properties shown in Table 4. The carburized magnesia raw material shown in Table 2 was used.

  In each example, 30 wt. Bitter solution as a binder was externally added to the formulation shown in the table at 4 wt%, and 1 batch was 50 kg and kneaded for 5 minutes with a Dalton mixer. The clay was molded into a normal shape with a hydraulic press under a pressure of 300 kg / cmm2. 110 ° C. × 10 hr. After drying, 1500 ° C. × 3 hr. Each test such as physical properties, erosion test, and spalling test was conducted by heating.

  Each test was conducted as follows.

Apparent porosity, bulk specific gravity: Measured according to JIS R2205-74.
Compressive strength: measured by JISR-76.
Linear change rate: 110 ° C. × 10 hr. It is a value after heating in a siliconite electric furnace based on after drying.
Erosion test: The amount of erosion and the amount of erosion were measured by a rotating drum type erosion test method and displayed as an index.
As the erodant, steel 80% + electric furnace slag (CaO / SiO ₂ = 3.0, totalFe = 15%) was used.
Spalling test: A normal type was used as a test piece, and a cycle of heating for 15 minutes and air cooling for 15 minutes was repeated 10 times, and the number of peeling occurrences was evaluated.
As can be seen by comparing the Examples and Comparative Examples in Table 3, the physical properties and corrosion resistance of the two are almost the same.

  Actual furnace test: Experiment No. The basic stamp material having the composition shown in 2-1, was actually applied to a 100 t electric furnace and evaluated. The workability was equivalent to the conventional product. There was no problem of boiling water that occurred when MgO-C brick was used as raw material. It was operated under the conditions of a molten steel temperature of 1650 ° C. and a blowing time of 40 minutes, and the durability was 10 to 15 times equivalent to the conventional one.

<Ladle spray material>
About the ladle spraying material of this invention, the Example and the comparative example (conventional example) which were tried in A steelworks were shown in Table 5. Table 4 shows chemical analysis values and physical property values of main refractory raw materials used in each example.

  As shown in Table 5, in the examples of the present invention, there was no pulsation at the time of spraying, and the rebound loss was about 10%, which was as low as the conventional product. There was no peeling as in the conventional product, and there was little smoke generation. The seizure and adhesion were also good.

  As described above, the amorphous refractory using the carburized MgO raw material of the present invention showed inferior characteristics and durability compared to conventional products.

Since the carburized raw material of the present invention is heat-treated with used MgO-C brick under appropriate conditions,
Because it is stable, in addition to the electric furnace stamp material and ladle spray repair material illustrated, it can also be applied to various irregular shaped refractories such as electric furnace spray repair materials, RH dip pipe spray repair materials, tundish ramming materials, etc. is there.

  In the present invention, since used MgO-C brick can be recycled and reused as a refractory aggregate with higher added value, it is useful not only for effective use of resources but also for recycling of waste. Also contribute significantly, and its industrial applicability is enormous.

Claims (3)

  Carburized raw material produced by firing of used carbon-containing unfired brick.   A carburized raw material produced by firing a used carbon-containing unfired brick under the conditions of an oxygen concentration of 5.0 to 9.0% and a temperature of 800 to 1000 ° C.   An amorphous refractory containing the carburized raw material according to claim 1.

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