JP2013249245A - Method for recycling used carbon-containing unfired brick - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide reclaimed brick having performance equal to or better than brick using virgin materials by reclaiming used carbon-containing unfired brick, to increase the recycling quantity of used unfired brick than before, and to reduce the scrap disposal volume.SOLUTION: Reclaimed brick is produced using a carburized material obtained by crushing used carbon-containing unfired brick and firing the crushed brick at oxygen concentration of 5.0-9.0% and a temperature of 800-1,000°C.

Description

  The present invention relates to a method of reusing waste refractory carbon-containing unfired brick generated in a steel factory or the like.

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 bricks, MgO bricks Various refractory bricks such as MgO—Cr ₂ O ₃ brick are used.

  Hereinafter, MgO—C brick will be described as a representative of carbon-containing unfired brick. MgO-C bricks have excellent corrosion resistance and spall resistance due to the high corrosion resistance of magnesia, the property of carbon that does 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. Spent bricks contain impurities generated during operation mainly on the operating surface side, so when recycled as MgO-C bricks as they are, equivalent performance cannot be obtained, so recycling with bricks is not much It was not progressing.

  For this reason, when recycling used MgO-C bricks, many are reground and used for slagging materials, or are sized and used as irregular repair materials, and many are buried at disposal sites. Has been processed. In addition, since a large amount of money is required for burying disposal, further expansion of the amount of recycling has been an issue.

  On the other hand, for example, the following recycling methods have been proposed. Patent Document 1 discloses a method of removing a deteriorated layer on the working surface side of MgO-C brick after use and adding a recycled material obtained by pulverizing the remainder to MgO-C brick.

  However, the recycled brick by the method disclosed in Patent Document 1 is to be reused in a mixed state containing different raw materials such as an organic binder and metal powder in the MgO-C brick. Since it could only be recovered in a state with a large amount of impurities mixed in, it did not exceed the characteristics of bricks using virgin raw materials.

  JP-A-8-319154

  An object of the present invention is to regenerate used MgO-C bricks and obtain MgO-C bricks having the above characteristics using MgO-C bricks using virgin raw materials.

  The present invention includes a regeneration step in which used MgO-C brick is pulverized, sized and fired to oxidize and separate magnesia and carbon, and a shaped refractory is produced using raw materials obtained in the regeneration step. It is characterized by.

  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 regenerated magnesia raw material having few and excellent characteristics can be obtained.

  The recycled magnesia raw material is obtained by subjecting used MgO-C bricks to coarse crushing and sieving to 10 mm or less by oxidation baking treatment. 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 (hereinafter referred to as a carburized magnesia raw material) obtained by carburizing magnesia with 0.5 to 7.0% by mass of carbon 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 by 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.

  The operation according to the present invention is as follows. MgO-C brick is known for its high corrosion resistance and excellent slag penetration resistance, but the oxidation of carbon is considered the biggest bottleneck. Therefore, metal powders such as Al and Si are added as an antioxidant. The MgO-C brick using the carburized magnesia raw material of the present invention is less susceptible to oxidation because carbon is present in the carburized state in magnesia, and moreover, compared to MgO-C brick with the same amount of carbon, scaly graphite Therefore, the conventional MgO-C brick has better oxidation resistance and low thermal conductivity.

  In addition, since used MgO-C bricks are subjected to repeated thermal history while being used as a steelmaking lining material, compared with the electrofused magnesia raw materials conventionally used for MgO-C bricks, The rate is high. From this, the MgO-C brick using the carburized magnesia raw material of the present invention has a low thermal conductivity and excellent heat resistance spalling property compared to the MgO-C brick of the same amount of carbon. Become.

Since the MgO-C brick using the carburized magnesia raw material according to the present invention uses the used MgO-C brick as a raw material, the range of recycling is widened and the amount of burying treatment can be reduced. Moreover, since the low heat conductive MgO-C brick can be provided, the heat loss of the steelmaking equipment is reduced, and the energy cost is reduced. Moreover, since the usage-amount of scaly graphite can be reduced when manufacturing the MgO-C brick of the same amount of carbon, it leads to a cost reduction.
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.

As the equipment used in the firing process, a single kiln, shuttle kiln, electric furnace, rotary kiln or the like can be used. However, it is desirable to use a rotary kiln in consideration of fuel consumption, oxidation process in firing process, and mass treatment.
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.

  Examples of the present invention will be described below to further clarify the features of the present invention.

  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 SiO2, 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 if only 5 to 1 mm is used for MgO-C brick Therefore, it can be expected to be a brick with better corrosion resistance.

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 apparent porosity is higher than that of the carburized magnesia raw material.

  Next, the recycled magnesia raw material obtained in the present invention was evaluated. The regenerated magnesia raw material obtained in the present invention is classified into 5 to 1 mm and 1 mm or less, 0 to 100% by mass is added, and the remainder is prepared so as to be fused magnesia, scaly graphite, and metal powder, and organic as a binder. After kneading using a solvent, press molding was performed. Thereby, a molded body of 230 × 180 × 65 mm was obtained. The molded body was dried at a maximum temperature of 250 ° C. for 24 hours to prepare a sample, and its characteristics were tested.

  Conventional Example 1 is a prototype using a virgin raw material without using a recycled raw material. Conventional Example 2 is a prototype of the used MgO-C brick shown in Table 2 that is used untreated.

Recycled magnesia raw materials were added in proportions shown in Table 3, and virgin magnesia aggregates were used as the other aggregates used. The added amount of scaly graphite was adjusted so that the total amount of carbon in the blended MgO-C brick was 6% by mass.

  The apparent porosity and bulk specific gravity were measured according to JIS R2205-74. In Experimental Examples 1 to 4 using the carburized magnesia raw material, as the amount of addition increases, a tendency of high apparent porosity and low bulk specific gravity tends to occur.

  The thermal conductivity was measured at 900 ° C. by a laser flash method. The thermal conductivity tends to decrease as the carburized magnesia raw material is added. This is thought to be due to the high apparent porosity of the carburized magnesia raw material and the decrease in the amount of scaly graphite added.

  The prepared sample was cut into 40 × 40 × 150 mm, fired in an electric furnace at 1500 ° C. for 3 hours, then cut, and the oxide layers at four cut surfaces were measured for each sample, and the average value was defined as the oxidation amount (mm).

  Regarding the oxidation amount, as the carburized magnesia raw material is added, the oxidation amount decreases and the oxidation resistance tends to be improved. This is thought to be due to the effect of carbon carburized in magnesia as described above.

The evaluation method of corrosion resistance is as follows.

  Erosion test at 1650 ° C x 6 hours x 2 days by rotating drum method under slag conditions with basicity of 2.0, measure the remaining size of 5 places per sample, and erod the average value of reduction from the original size Amount (mm).

  From the results of the erosion test, the amount of erosion tended to decrease as carburized magnesia material was added. In general, when a magnesia raw material having a high apparent porosity and a low bulk specific gravity is used, even in MgO-C brick, a phenomenon that the corrosion resistance of the brick is lowered due to a high apparent porosity and a low bulk specific gravity is observed. In this test, it was confirmed that by using carburized magnesia raw material, corrosion resistance superior to that of virgin products can be obtained even with high apparent porosity.

  As described above, the present invention recycles the carburized magnesia raw material obtained by pulverizing and firing the used MgO-C brick into MgO-C brick, so that the MgO-C brick using the conventional virgin raw material is used. Compared to the above, it has improved oxidation resistance and corrosion resistance, and has low heat conductivity.

Although the present invention can be applied to carbon-containing unfired bricks, an example of an embodiment was shown for MgO-C bricks. The present invention can also be applied to Al ₂ O ₃ —MgO—C brick.

  Carbon-containing unfired bricks have a disadvantage of so-called carbon pick-up due to the deterioration of the quality of steel products due to the dissolution of carbon components in steelmaking ladles, RH furnaces, etc., but by using the carburized magnesia raw material of the present invention, carbon It is expected to be effective in picking up measures.

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

Claims (3)

A method for recycling and recycling used carbon-containing unfired bricks, characterized by firing used carbon-containing unfired bricks A method for recycling and recycling used carbon-containing unfired bricks, characterized by firing at an oxygen concentration of 5.0 to 9.0% and a temperature of 800 to 1000 ° C. Regeneration of used MgO-C brick, characterized by producing a MgO-C brick using a carburized magnesia raw material obtained by firing at an oxygen concentration of 5.0-9.0% and a temperature of 800-1000 ° C. Reuse method