Method for producing recycled refractory raw materials

Abstract

To provide a method for producing recycled refractory raw materials that can process carbon-containing refractories composed of raw materials with large particle sizes while reducing the amount of energy used. 【Solution means】In a method for producing recycled refractory raw materials using carbon-containing refractory bricks, it includes a granulation step of granulating the carbon-containing refractory bricks to obtain granulated bricks, and a heat treatment step of heating the granulated bricks while supplying an oxidizing gas into a fluidized roasting furnace.

Description

Technical Field

[0001] The present invention relates to a method for producing recycled refractory raw materials using carbon-containing refractory bricks.

Background Art

[0002] The recycling of carbon-containing refractories has been promoted for the purpose of effective use of resources. For example, a recycling method for reducing the carbon content of used carbon-containing refractories by heat treatment is known.

[0003] Patent Document 1 discloses a granulation step of granulating carbon-containing refractory bricks to obtain granulated bricks, and a heat treatment step of heating the granulated bricks in an externally heated rotary kiln in the presence of an oxidizing gas to obtain recycled refractory raw materials. In the heat treatment step, the heating temperature is 850°C or higher and 1000°C or lower, and the heating time is 4 hours or longer.

[0004] Patent Document 2 discloses a method for recycling casting sand, characterized in that used casting sand with a carbon component attached is housed in a combustion furnace, a vacuum pump is connected to one side of the combustion furnace, the other side is opened, air is introduced into the casting sand by suction of the vacuum pump, and the deposit is ignited on the upwind side of the air flow, and the combustion part of the deposit is sequentially moved to the downwind side to burn and remove the deposit on the casting sand.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the method for producing a recycled refractory raw material described in Patent Document 1, a large amount of energy is required to continuously heat at 850°C or higher and 1000°C or lower in an externally heated rotary kiln, and there are still challenges in reducing the CO2 emissions associated with energy use.

[0007] In the method for recycling foundry sand described in Patent Document 2, although the adherents (carbides) attached to the foundry sand can be removed, the particle size of the foundry sand is generally less than 1 mm. On the other hand, the raw materials for refractories used in steelworks, etc., have various particle sizes, and those with a particle size larger than 1 mm also exist. It is difficult to process refractory raw materials with a particle size larger than 1 mm by the method for recycling foundry sand described in Patent Document 2.

[0008] An object of the present invention is to provide a method for producing a recycled refractory raw material that can reduce the amount of energy used and can also process carbon-containing refractories composed of raw materials with a large particle size.

Means for Solving the Problems

[0009] The method for producing a recycled refractory raw material according to the present invention is a method for producing a recycled refractory raw material using carbon-containing refractory bricks, a granulation step of granulating the carbon-containing refractory bricks to obtain granulated bricks, a heat treatment step of heating the granulated bricks while supplying an oxidizing gas into a fluidized roasting furnace, characterized by including these steps.

[0010] According to this configuration, even in the case of a carbon-containing refractory with a large particle size, the heating temperature and heating time can be reduced, and the energy consumption can be reduced compared with the prior art. That is, it is possible to produce a recycled refractory raw material with a sufficiently reduced carbon content while reducing the CO2 emissions.

[0011] In one aspect, the method for producing a recycled refractory raw material according to the present invention preferably has a heating temperature in the heat treatment step of 700°C or higher and 900°C or lower.

[0012] With this configuration, by heating at a temperature of 700 °C or higher and 900 °C or lower, the carbon contained in the granulated carbon-containing refractory bricks can be preferably converted into carbon dioxide, so that carbon can be efficiently removed from the carbon-containing refractory bricks.

[0013] As one aspect, in the method for producing a recycled refractory raw material according to the present invention, it is preferable that the superficial gas velocity in the fluidized roasting furnace is 0.5 m / s or more and 16.7 m / s or less.

[0014] According to this configuration, the granulated bricks can be efficiently stirred in the fluidized roasting furnace, and at the same time, it is also possible to make the carbon more easily self-ignite during stirring.

[0015] As one aspect, in the method for producing a recycled refractory raw material according to the present invention, it is preferable that the heating time in the heat treatment step is 4 hours or less.

[0016] According to this configuration, the heating time is shortened compared with the prior art, and energy consumption can be reduced.

[0017] As one aspect, in the method for producing a recycled refractory raw material according to the present invention, it is preferable that the input amount of the granulated bricks into the fluidized roasting furnace is 0.01 t / h or more and 1.00 t / h or less.

[0018] According to this configuration, the granulated bricks can be efficiently exposed to an oxidizing atmosphere.

[0019] As one aspect, in the method for producing a recycled refractory raw material according to the present invention, it is preferable that the carbon content of the recycled refractory raw material is 2.0% by mass or less.

[0020] According to this configuration, a recycled refractory raw material that can be used as a raw material for refractories for a wide range of applications can be obtained.

[0021] As one aspect, in the method for producing a recycled refractory raw material according to the present invention, it is preferable that the carbon-containing refractory bricks are magnesia-carbonaceous carbon-containing refractory bricks.

[0022] According to this configuration, since a recycled refractory raw material containing magnesia can be obtained, the amount of naturally derived magnesia raw material used can be suppressed.

Embodiments for Carrying Out the Invention

[0023] An embodiment of a method for manufacturing a recycled refractory raw material according to the present invention will be described.

[0024] The method for manufacturing a recycled refractory raw material according to this embodiment includes a granulation step of granulating a carbon-containing refractory brick to obtain granulated bricks, and a heat treatment step of heating the granulated bricks while supplying an oxidizing gas into a fluidized roasting furnace, and is a method for manufacturing a recycled refractory raw material using a carbon-containing refractory brick as a starting material. In addition, in the method for manufacturing a recycled refractory raw material according to the present invention, a removal step and a classification step may be further carried out as necessary.

[0025] 〔Carbon-containing refractory brick〕 The definition of the term "refractory brick" follows JIS R2001-1985. That is, "refractory brick" means "refractory materials having various forms suitable for constructing kilns and other structures used at high temperatures". The term "carbon-containing refractory brick" represents those containing carbon among the refractory bricks defined as above.

[0026] The carbon-containing refractory brick in this embodiment contains a metal oxide and carbon. The carbon-containing refractory brick is classified according to the type of metal oxide contained. For example, types such as magnesia-carbon, spinel-carbon, magnesia-spinel-carbon, alumina-carbon, and alumina-silicon carbide-carbon are exemplified. As the carbon-containing refractory brick used as a starting material in the method for manufacturing a recycled refractory raw material according to this embodiment, any carbon-containing refractory brick including those exemplified above can be used.

[0027] When the carbon content of the carbon-containing refractory brick is 50% by mass or less, it is preferable because it is easy to obtain a recycled refractory raw material with a carbon content of 1% by mass or less. The carbon content of the carbon-containing refractory brick is more preferably 50% by mass or less, and even more preferably 25% by mass or less. The lower limit of the carbon content of the carbon-containing refractory brick is not particularly limited. For example, the carbon content of the carbon-containing refractory brick can be 1.0% by mass or more.

[0028] Typically, the carbon-containing refractory brick is obtained by kneading a refractory raw material, which is a raw material containing a metal oxide, a carbon raw material, which is a raw material containing carbon, and any other additives (such as binders and additives), forming the resulting mixture, and further heat-treating it. Here, the type of the carbon-containing refractory brick obtained corresponds to the metal oxide contained in the selected refractory raw material. The refractory raw material and the carbon raw material are generally provided in powder form, but are not limited thereto. The obtained carbon-containing refractory brick is widely used, for example, in locations in the steel manufacturing process where it comes into contact with molten metal, and an appropriate type of carbon-containing refractory brick is selected according to the location of use.

[0029] In the method for producing a recycled refractory raw material according to the present embodiment, a used carbon-containing refractory brick can be used as the carbon-containing refractory brick as the starting material. Here, the used carbon-containing refractory brick refers to a carbon-containing refractory brick having a history of use in a steel manufacturing process or the like. Obtaining a recycled refractory raw material using the used carbon-containing refractory brick as the starting material has significance as a method for recycling the used carbon-containing refractory brick.

[0030] As described above, in the method for producing a recycled refractory raw material according to the present embodiment, the type of the carbon-containing refractory brick as the starting material is arbitrary, but it is preferable to use a single type of carbon-containing refractory brick. This is because in this case, the recycled refractory raw material can be obtained as a single type of refractory raw material, making it easier to use the recycled refractory raw material as a raw material for bricks. Therefore, the method for producing a recycled refractory raw material according to the present embodiment may include a classification step of classifying carbon-containing refractory bricks by type.

[0031] For example, it is preferable to use a carbon-containing refractory brick containing magnesia (a magnesia-carbon type carbon-containing refractory brick) as a starting material. This is because if a carbon-containing refractory brick containing magnesia is used as a starting material, a recycled refractory raw material containing magnesia can be obtained, so that the amount of naturally-derived magnesia raw material used can be suppressed. In particular, in Japan, since much of the magnesia raw material depends on imports, it is desired to suppress the amount of naturally-derived magnesia raw material used. Further, when a magnesia-carbon type carbon-containing refractory brick is recycled by a conventional technique, the ratio of magnesia contained in the obtained recycled refractory raw material may be lower than that of the starting material (the magnesia yield is low). However, according to the method for producing a recycled refractory raw material according to the present embodiment, magnesia can be recycled at a relatively high yield.

[0032] 〔Removal step〕 The carbon-containing refractory bricks used and recovered at a steelworks or the like may contain aluminum carbide. Aluminum carbide is generated when a carbon-containing refractory brick added with metallic aluminum is used in a steel manufacturing process. If aluminum carbide is contained in the brick, it may cause cracks in the brick after molding or after shipment, so it is desirable to remove it. As a method for removing aluminum carbide contained in the used carbon-containing refractory brick, for example, it can be removed by a known method such as contacting with water or leaving it outdoors. When aluminum carbide expands due to hydration, the structure of the used carbon-containing refractory brick is destroyed and it naturally becomes fine-grained. In this case, the energy consumption in the fine-graining step can be reduced as compared with the case of using a machine such as a pulverizer.

[0033] Further, the used carbon-containing refractory brick may have metal, slag, etc. adhering thereto, which are derived from the process and location where the carbon-containing refractory brick was used. Therefore, in the method for producing a recycled refractory raw material according to the present embodiment, a keren treatment step or the like for removing the metal, slag, etc. adhering to the carbon-containing refractory brick may be carried out as necessary.

[0034] 〔Fine-graining step〕 The granulation step is a step of granulating carbon-containing refractory bricks to obtain granulated bricks.

[0035] As the method for carrying out the granulation step, any method can be used as long as it can granulate carbon-containing refractory bricks. The granulation step may include, for example, pulverizing carbon-containing refractory bricks. In this case, a known pulverizing device such as a jaw crusher is used to pulverize the carbon-containing refractory bricks.

[0036] In the granulation step, it is preferable to set conditions so that the maximum particle size of the obtained granulated bricks is 35 mm or less, because the oxidation of carbon is likely to proceed. The adjustment of the maximum particle size may be realized by setting the conditions of the pulverizing device as exemplified above, or may be realized by a method of removing components having a particle size exceeding 35 mm from the granulated bricks. The latter method can be carried out, for example, using a sieve with a nominal aperture of 31.5 mm specified in JIS Z8801-1. The maximum particle size of the granulated bricks obtained in the granulation step is more preferably 35 mm or less, and even more preferably 10 mm or less. The lower limit of the maximum particle size of the granulated bricks obtained in the granulation step is not particularly limited, but may be, for example, 1 mm or more.

[0037] In addition, in the structure of the magnesia-carbonaceous carbon-containing refractory bricks after use that have been granulated, magnesia particles and composite particle aggregates may exist. Here, the "composite particle aggregate" is defined as a composite particle aggregate in which magnesia particles and graphite particles are intricately intertwined in a part of the structure of the magnesia-carbonaceous carbon-containing refractory bricks after use.

[0038] 〔Heat treatment step〕 The heat treatment step is a step of heating the granulated carbon-containing refractory bricks while supplying an oxidizing gas into a fluidized roasting furnace to obtain a regenerated refractory raw material.

[0039] The oxidizing gas may be air or an oxygen-enriched gas. As the apparatus used for carrying out the heat treatment step, a known batch-type or continuous fluidized roasting furnace can be used. Among these, when a continuous-type apparatus is used, the heat treatment step can be continuously carried out, which is preferable because the efficiency of the entire manufacturing method of the regenerated refractory raw material is improved.

[0040] Note that the fluidized roasting furnace in the present embodiment means an apparatus that supplies and blows an oxidizing gas from the bottom of the furnace to promote spontaneous combustion of raw material particles while fluidizing and roasting the raw material particles.

[0041] (Heating temperature) The heating temperature in the heat treatment step is preferably 700°C or higher and 900°C or lower, more preferably 800°C or higher and 850°C or lower. By heating at a temperature of 700°C or higher and 900°C or lower, the carbon contained in the fine-grained carbon-containing refractory bricks can be suitably converted into carbon dioxide, so that carbon can be efficiently removed from the carbon-containing refractory bricks. Thereby, the carbon content of the obtained regenerated refractory raw material can be reduced to 2% by mass or less. In the conventional external heating method, it was necessary to set the temperature at 850°C or higher, whereas according to the present invention, it can be set at 850°C or lower.

[0042] (Heating time) The heating time of the heat treatment step in the present embodiment can be 4 hours or less. Thereby, the heating time is shortened compared with the prior art, and energy consumption can be reduced. On the other hand, when considering sufficiently removing the carbon contained in the fine-grained carbon-containing refractory bricks, it is more preferable that the heating time is 2 hours or more and 4 hours or less, and further preferably 3 hours or more and 4 hours or less. However, since the heating time at which the carbon content of the obtained regenerated refractory raw material becomes 2% by mass or less can vary depending on various conditions such as the particle size of the fine-grained carbon-containing refractory bricks, the temperature and atmosphere of the heat treatment step, and the apparatus used in the heat treatment step, the heating time may be appropriately set according to the actual implementation conditions.

[0043] (Empty tower velocity) The superficial velocity is calculated by dividing the volumetric flow rate of the fluid flowing through the tower under standard conditions by the cross-sectional area of the tower.

[0044] In the heat treatment process, the superficial velocity of the oxidizing gas blown into the fluidized roasting furnace is preferably 0.5 m / s or more and 16.7 m / s or less, more preferably 0.5 m / s or more and 10.0 m / s or less, and even more preferably 1.0 m / s or more and 5.0 m / s or less. By setting it within this range, it becomes easier to stably fluidize and stir the packed bed of fine-grained bricks in the fluidized roasting furnace, and at the same time, it becomes easier for carbon to self-ignite during stirring. In particular, if the superficial velocity is 16.7 m / s or less, it is less likely for the temperature inside the furnace to decrease.

[0045] In addition, when using fine-grained magnesia-carbonaceous carbon-containing refractory bricks after use, when the particles collide with each other and an impact is applied during combustion, the composite particle aggregate contained in the carbon-containing refractory brick is destroyed, and magnesium oxide (MgO) and carbon are peeled and separated, and it is considered that carbon is more easily combusted and removed. When carbon starts to self-ignite and the temperature of the furnace rises, heating can be stopped, and further reduction of the energy used is possible.

[0046] (Input amount) In the heat treatment process, the input amount of the fine-grained bricks into the fluidized roasting furnace can be appropriately changed according to the volume of the fluidized roasting furnace, etc. For example, when setting the input amount assuming a furnace with dimensions of diameter 2000 mm × height 8000 mm, the input amount is preferably 0.01 t / h or more and 1.00 t / h or less, and more preferably 0.20 t / h or more and 0.70 t / h or less. By setting it to 0.01 t / h or more and 1.00 t / h or less, the fine-grained bricks can be efficiently exposed to the oxidizing atmosphere. If the input amount is more than 0.01 t / h, it becomes easier for carbon to self-ignite during oxidative firing, and additional heating by a burner or the like becomes unnecessary, resulting in a decrease in CO2 emissions, which is preferable. Also, if the input amount is less than 1.00 t / h, it becomes difficult for the temperature inside the furnace to rise rapidly, and phenomena such as the furnace breaking or heat loss are less likely to occur.

[0047] The carbon content of the recycled refractory raw material obtained by the heat treatment process of this embodiment is preferably 2% by mass or less, more preferably 1.0% by mass or less. Also, the lower limit of the carbon content of the obtained recycled refractory raw material is not particularly limited, but is more than 0% by mass (note that the closer the carbon content is to 0% by mass, the better).

[0048] In particular, when using magnesia carbonaceous carbon-containing refractory bricks after use, the recycled refractory raw material obtained in the heat treatment process of this embodiment can be reused as a magnesia raw material in various refractories. For example, after being used in the production of magnesia carbon bricks, it can be recycled and reused to produce magnesia carbon bricks again, and can be effectively utilized repeatedly many times.

[0049] 〔Classification process〕 The classification process (particle size adjustment process) is a process of sieving the recycled refractory raw material and classifying it into a first component that does not pass through the sieve and a second component that passes through the sieve. The classification process can be carried out, for example, using a known sieving device equipped with a sieve with a nominal mesh size of 300 μm specified in JIS Z8801-1.

[0050] The first component obtained in the classification process is relatively high in purity and suitable for use as an aggregate. Therefore, the first component can be used as a raw material for refractories that require high purity, such as shaped refractories.

[0051] On the other hand, the second component obtained by the classification process contains ash and the like, so its purity is relatively low. Therefore, the second component can be used as a raw material for general-purpose refractories that require a relatively low purity level, such as unshaped refractories.

[0052] Also, in the classification process, the recycled refractory raw material may be classified into a plurality of grades. In this case, since the recycled refractory raw material classified into a predetermined particle size range is obtained, it becomes easier to use it appropriately according to the purpose when using the recycled refractory raw material as a refractory raw material.

Examples

[0053] An embodiment of the present invention will be described. First, an experiment was conducted in which magnesia-carbonaceous carbon-containing refractory bricks after use were granulated, and the obtained granulated bricks were roasted in a fluidized roasting furnace, and the following items were measured.

[0054] (Empty tower velocity) The empty tower velocity was measured by installing a differential pressure type flow meter at the nozzle through which gas was introduced into the furnace from the blower, and was calculated by dividing the volume flow rate at standard conditions by the tower cross-sectional area.

[0055] (Carbon content) Free carbon (F.C) was measured in accordance with JIS R2011:2007.

[0056] (Experiment 1) The granulated bricks were sieved, and the granulated bricks with a particle size of 5 mm were charged into a fluidized roasting furnace and subjected to a heat treatment process. The charging amount was set to 0.57 t / h, and the carbon content when each of the heating temperature, heating time, and empty tower velocity was changed is shown in Table 1.

Table 1

[0057] (Experiment 2) Similar to Experiment 1, the granulated bricks with a particle size of 5 mm were charged into a fluidized roasting furnace, and a heat treatment process was performed with the heating temperature set to 800 °C, the heating time set to 2 hours, and the empty tower velocity set to 1.5 m / s. The carbon content when the charging amount of the granulated bricks was changed under these conditions is shown in Table 2.

Table 2

[0058] For the evaluation, in both Table 1 and Table 2, those with a carbon content of 1 mass% or less after treatment were judged as "excellent", those with more than 1% and 2% or less were judged as "good", and those exceeding 2 mass% were judged as "unacceptable".

[0059] Examples 1 to 8 and Comparative Example in Table 1 are those in which the respective heating temperatures, heating times, and superficial gas velocities were changed. In all of Examples 1 to 8, regenerated refractory raw materials with a sufficiently reduced carbon content were obtained. On the other hand, in the Comparative Example, the carbon content was not sufficiently reduced. In the Comparative Example, the superficial gas velocity was set to 0 m / s, that is, stirring was not performed without supplying an oxidizing gas to the fluidized roasting furnace, resulting in insufficient stirring force and making it difficult to break the composite particle aggregates. As a result, it is considered that the spontaneous combustion of carbon was not promoted.

[0060] Examples 9 to 11 in Table 2 are those in which the input amount of the granulated bricks was changed. In all cases, regenerated refractory raw materials with a sufficiently reduced carbon content were obtained.

Claims

1. A method for producing recycled refractory raw material using carbon-containing refractory bricks, comprising the steps of: a granulation step of granulating the carbon-containing refractory brick to obtain a granulated brick; a heat treatment step of heating the granulated bricks while supplying an oxidizing gas into a fluidized roasting furnace, The method for producing a recycled refractory raw material, wherein the heating temperature in the heat treatment step is 700° C. or higher and 900° C. or lower.

2. The method for producing a recycled refractory raw material according to claim 1, wherein the superficial velocity in the fluidized roasting furnace is 0.5 m / s or more and 16.7 m / s or less.

3. The method for producing a recycled refractory raw material according to claim 1, wherein the heating time in the heat treatment step is 4 hours or less.

4. 2. The method for producing a recycled refractory raw material according to claim 1, wherein the amount of the granulated bricks fed to the fluidized roasting furnace is 0.01 t / h or more and 1.00 t / h or less.

5. A method for producing recycled refractory raw material using carbon-containing refractory bricks, comprising: a granulation step of granulating the carbon-containing refractory brick to obtain a granulated brick; a heat treatment step of heating the granulated bricks while supplying an oxidizing gas into a fluidized roasting furnace, The method for producing the recycled refractory raw material, wherein the recycled refractory raw material has a carbon content of 2.0 mass% or less.

6. 6. The method for producing a recycled refractory raw material according to claim 1, wherein the carbon-containing refractory brick is a magnesia-carbonaceous carbon-containing refractory brick.

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