Method for producing recycled refractory raw material

Abstract

To provide a method for producing recycled refractory raw material, capable of processing carbon-containing refractories composed of raw materials having a large particle size while reducing an amount of energy used.SOLUTION: A method for producing recycled refractory raw material using a carbon-containing refractory brick includes: a pulverizing step of finely pulverizing the carbon-containing refractory brick to obtain a finely pulverized brick; and a heating step of heating the finely pulverized brick while supplying an oxidizing gas into a fluidized roasting furnace.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Recycling of carbon-containing refractories has been promoted for the purpose of effective utilization of resources. For example, a regeneration method is known in which the carbon content of used carbon-containing refractories is reduced by heat treatment.

[0003] Patent Document 1 discloses a method for producing a recycled refractory raw material, which includes a grain refining step of obtaining refined bricks by grain refining carbon-containing refractory bricks, and a heat treatment step of heating the refined bricks in an externally heated rotary kiln in the presence of an oxidizing gas to obtain a recycled refractory raw material, wherein the heating temperature in the heat treatment step is 850°C or higher and 1000°C or lower, and the heating time in the heat treatment step is 4 hours or longer.

[0004] Patent Document 2 discloses a method for regenerating foundry sand, which comprises placing used foundry sand with carbon components attached in a combustion furnace, connecting a vacuum pump to one side of the furnace and leaving the other side open, introducing air into the foundry sand by suction with the vacuum pump, igniting the deposits on the upwind side of the air flow, and gradually moving the burning part of the deposits to the downwind side, thereby burning and removing the deposits from the foundry sand. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2024-013030 [Patent Document 2] Patent No. 3138479 Summary of the Invention [Problem to be solved by the invention]

[0006] The method for producing recycled refractory raw materials described in Patent Document 1 requires a large amount of energy to continue heating at 850°C to 1000°C for four hours or more in an externally heated rotary kiln, and there is also the issue of reducing CO2 emissions associated with energy consumption.

[0007] The foundry sand reclamation method described in Patent Document 2 can remove deposits (carbides) that have adhered to foundry sand, but foundry sand generally has a small particle size of less than 1 mm. Meanwhile, refractory raw materials used in steelworks and other facilities have a variety of particle sizes, including some larger than 1 mm. The foundry sand reclamation method described in Patent Document 2 has difficulty processing refractory raw materials with particle sizes larger than 1 mm.

[0008] An object of the present invention is to provide a method for producing recycled refractory raw materials which can reduce the amount of energy used and can also process carbon-containing refractories made up of raw materials with large particle sizes. [Means for solving the problem]

[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 a carbon-containing refractory brick, comprising: a granulation step of granulating the 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.

[0010] According to this method, the heating temperature and heating time can be reduced even for carbon-containing refractories with large particle sizes, and energy consumption can be reduced compared to conventional techniques. In other words, it is possible to produce recycled refractory raw materials with a sufficiently reduced carbon content while reducing CO2 emissions.

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

[0012] By heating at a temperature of 700°C or higher and 900°C or lower as in this configuration, the carbon contained in the finely divided carbon-containing refractory bricks can be suitably converted into carbon dioxide, thereby making it possible to efficiently remove carbon from the carbon-containing refractory bricks.

[0013] In one aspect of the method for producing a recycled refractory raw material according to the present invention, the superficial velocity in the fluidized bed roaster is preferably 0.5 m / s or more and 16.7 m / s or less.

[0014] According to this configuration, the finely divided bricks can be efficiently agitated in the fluidized bed roasting furnace, and further, simultaneously with the agitation, it is possible to make the carbon more likely to self-combust.

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

[0016] According to this configuration, the heating time can be shortened compared to the conventional technology, thereby reducing energy consumption.

[0017] In one aspect of the method for producing a recycled refractory raw material according to the present invention, the amount of the granulated bricks fed into the fluidized bed roaster is preferably 0.01 t / h or more and 1.00 t / h or less.

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

[0019] In one aspect of the method for producing a recycled refractory raw material according to the present invention, the recycled refractory raw material preferably has a carbon content of 2.0 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] In one embodiment of the method for producing a recycled refractory raw material according to the present invention, the carbon-containing refractory brick is preferably a magnesia-carbonaceous carbon-containing refractory brick.

[0022] According to this configuration, a recycled refractory raw material containing magnesia can be obtained, so that the amount of naturally occurring magnesia raw material used can be reduced. DETAILED DESCRIPTION OF THE INVENTION

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

[0024] The method for producing a recycled refractory raw material according to this embodiment includes a refining step of refining carbon-containing refractory bricks to obtain refining bricks, and a heat treatment step of heating the refining bricks while supplying an oxidizing gas into a fluidized roasting furnace, and is a method for producing a recycled refractory raw material using carbon-containing refractory bricks as a starting raw material. Note that the method for producing a recycled refractory raw material according to the present invention may further include a removing step and a classifying step, if necessary.

[0025] [Carbon-containing refractory bricks] The definition of the term "refractory brick" follows JIS R2001-1985. That is, "refractory brick" means "refractories of various shapes suitable for the construction of kilns and other structures used at high temperatures." Furthermore, the term "carbon-containing refractory brick" refers to refractory bricks defined above that contain carbon.

[0026] The carbon-containing refractory brick in this embodiment contains a metal oxide and carbon. Carbon-containing refractory bricks are classified according to the type of metal oxide they contain, and examples thereof include magnesia carbonaceous, spinel carbonaceous, magnesia spinel carbonaceous, alumina carbonaceous, and alumina silicon carbide carbonaceous. Any carbon-containing refractory brick, including the types exemplified above, can be used as the carbon-containing refractory brick used as the starting material in the method for producing a recycled refractory raw material according to this embodiment.

[0027] A carbon content of the carbon-containing refractory brick of 50% by mass or less is preferred 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. There is no particular lower limit for the carbon content of the carbon-containing refractory brick, but for example, the carbon content of the carbon-containing refractory brick may be 1.0% by mass or more.

[0028] Carbon-containing refractory bricks are typically obtained by kneading a refractory raw material containing a metal oxide, a carbon raw material containing carbon, and any other additives (such as a binder or additive), shaping the resulting mixture, and then heat-treating the mixture. The type of carbon-containing refractory brick obtained here 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 this is not limitative. The obtained carbon-containing refractory bricks are widely used, for example, in locations that come into contact with molten metal in steelmaking processes, and an appropriate type of carbon-containing refractory brick is selected depending on the location where it is used.

[0029] In the method for producing a recycled refractory raw material according to this embodiment, a used carbon-containing refractory brick can be used as the carbon-containing refractory brick used as the starting raw material. Here, the used carbon-containing refractory brick refers to a carbon-containing refractory brick that has a history of being used in a steel production process or the like. Obtaining a recycled refractory raw material from a used carbon-containing refractory brick as the starting raw material is significant as a method for reusing used carbon-containing refractory bricks.

[0030] As described above, in the method for producing a recycled refractory raw material according to this embodiment, any type of carbon-containing refractory brick may be used as the starting raw material, but it is preferable to use a single type of carbon-containing refractory brick. In this case, the recycled refractory raw material is 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 this embodiment may include a classification step of classifying the carbon-containing refractory bricks by type.

[0031] For example, it is preferable to use a carbon-containing refractory brick containing magnesia (a magnesia-carbonaceous carbon-containing refractory brick) as the starting material. This is because, if a carbon-containing refractory brick containing magnesia is used as the starting material, a recycled refractory raw material containing magnesia can be obtained, thereby reducing the amount of naturally occurring magnesia raw material used. In particular, Japan relies on imports for much of its magnesia raw material, so it is desirable to reduce the amount of naturally occurring magnesia raw material used. Furthermore, when a magnesia-carbonaceous carbon-containing refractory brick is recycled using conventional technology, the proportion of magnesia contained in the resulting recycled refractory raw material is sometimes lower than that of the starting material (low magnesia yield). However, according to the method for producing a recycled refractory raw material according to this embodiment, magnesia can be recycled at a relatively high yield.

[0032] [Removal process] Carbon-containing refractory bricks used in steelworks and other facilities and then recovered may contain aluminum carbide. Aluminum carbide is generated when carbon-containing refractory bricks containing added metallic aluminum are used in the steel manufacturing process. Aluminum carbide present in bricks can cause cracks in the bricks after molding or shipping, so it is desirable to remove it. Aluminum carbide contained in used carbon-containing refractory bricks can be removed by known methods, such as contacting them with water or leaving them in the open air. When aluminum carbide expands due to hydration, the structure of the used carbon-containing refractory brick is destroyed, naturally resulting in fine grains. This method reduces the energy consumption in the grain refinement process compared to using a machine such as a crusher.

[0033] Furthermore, used carbon-containing refractory bricks may have metals, slag, etc., attached thereto, which are derived from the process and location in which the carbon-containing refractory bricks were used. Therefore, in the method for producing a recycled refractory raw material according to this embodiment, a scraping process or the like may be carried out as necessary to remove metals, slag, etc., attached to the carbon-containing refractory bricks.

[0034] [Refining process] The grain refining step is a step of refining the carbon-containing refractory brick to obtain a grain-refined brick.

[0035] The method for carrying out the particle size reduction step can be any method as long as it can reduce the particle size of the carbon-containing refractory brick. The particle size reduction step can include, for example, crushing the carbon-containing refractory brick. In this case, the carbon-containing refractory brick is crushed using a known crushing device such as a jaw crusher.

[0036] In the grain refining step, it is preferable to set the conditions so that the maximum particle size of the resulting refined bricks is 35 mm or less, as this facilitates carbon oxidation. The adjustment of the maximum particle size may be achieved by setting the conditions of the crushing device as exemplified above, or by removing components with particle sizes exceeding 35 mm from the refined bricks. The latter method can be performed, for example, using a sieve with a nominal mesh size of 31.5 mm as specified in JIS Z8801-1. The maximum particle size of the refined bricks obtained in the grain refining step is more preferably 35 mm or less, and even more preferably 10 mm or less. There is no particular limitation on the lower limit of the maximum particle size of the refined bricks obtained in the grain refining step, but it can be, for example, 1 mm or more.

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

[0038] [Heat treatment process] The heat treatment step is a step in which the finely granulated carbon-containing refractory bricks are heated in a fluidized roasting furnace while supplying an oxidizing gas, thereby obtaining a recycled refractory raw material.

[0039] The oxidizing gas may be air or an oxygen-enriched gas. A known batch or continuous fluidized bed roaster can be used as the apparatus for carrying out the heat treatment step. Among these, the use of a continuous apparatus is preferred because it allows the heat treatment step to be carried out continuously, thereby improving the overall efficiency of the method for producing a recycled refractory raw material.

[0040] In this embodiment, the fluidized bed roasting furnace refers to an apparatus that supplies an oxidizing gas from the bottom of the furnace to raw material particles and blows it upward to promote spontaneous combustion of the raw material particles while fluidizing them and roasting them.

[0041] (Heating temperature) The heating temperature in the heat treatment step is preferably 700°C or higher and 900°C or lower, and 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 finely divided carbon-containing refractory bricks can be suitably converted into carbon dioxide, thereby efficiently removing carbon from the carbon-containing refractory bricks. This makes it possible to reduce the carbon content of the resulting recycled refractory raw material to 2% by mass or lower. While conventional external heating requires a temperature of 850°C or higher, the present invention makes it possible to reduce the temperature to 850°C or lower.

[0042] (Heating time) The heating time in the heat treatment step in this embodiment can be set to 4 hours or less. This shortens the heating time compared to conventional techniques, thereby reducing energy consumption. On the other hand, when considering sufficient removal of carbon contained in the finely divided carbon-containing refractory bricks, the heating time is more preferably set to 2 hours or more and 4 hours or less, and even more preferably set to 3 hours or more and 4 hours or less. However, the heating time required for the carbon content of the resulting recycled refractory raw material to be 2 mass% or less can vary depending on various conditions, such as the particle size of the finely divided carbon-containing refractory bricks, the temperature and atmosphere of the heat treatment step, and the equipment used in the heat treatment step. Therefore, the heating time may be set appropriately depending on the actual implementation conditions.

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

[0044] In the heat treatment step, the superficial velocity of the oxidizing gas blown into the fluidized roasting furnace is preferably 0.5 m / s to 16.7 m / s, more preferably 0.5 m / s to 10.0 m / s, and even more preferably 1.0 m / s to 5.0 m / s. By setting the superficial velocity within this range, the packed bed of fine-grained bricks can be stably fluidized and stirred in the fluidized roasting furnace, and carbon can easily self-combust during stirring. In particular, setting the superficial velocity to 16.7 m / s or less makes it difficult for the temperature inside the furnace to drop.

[0045] Furthermore, when used finely granulated magnesia-carbon refractory bricks are used, the particles collide with each other during combustion, causing an impact, which breaks down the composite particle aggregates contained in the carbon-containing refractory bricks, causing the magnesium oxide (MgO) and carbon to separate, making it easier to burn and remove the carbon. Once the carbon begins to self-combust and the furnace temperature rises, heating can be stopped, allowing for further reductions in energy consumption.

[0046] (Input amount) In the heat treatment process, the amount of refined bricks fed into the fluidized roasting furnace can be varied as appropriate depending on the volume of the furnace. For example, when setting the amount of feed assuming a furnace with dimensions of 2000 mm in diameter and 8000 mm in height, the amount of feed is preferably 0.01 t / h to 1.00 t / h, and more preferably 0.20 t / h to 0.70 t / h. By setting the amount of feed to 0.01 t / h to 1.00 t / h, the refined bricks can be efficiently exposed to an oxidizing atmosphere. A feed rate of more than 0.01 t / h is preferable because it facilitates spontaneous combustion of carbon during oxidizing firing, eliminating the need for additional heating using a burner or the like and reducing CO2 emissions. Furthermore, a feed rate of less than 1.00 t / h prevents a rapid increase in the furnace temperature, reducing the risk of furnace damage or heat loss.

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

[0048] In particular, when a used magnesia-carbonaceous carbon-containing refractory brick is used, the recycled refractory raw material obtained by the heat treatment step of this embodiment can be reused as a magnesia raw material for various refractories. For example, after being used to manufacture a magnesia-carbon brick, the recycled refractory raw material can be reused many times, for example, by carrying out a regeneration treatment to manufacture a magnesia-carbon brick again.

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

[0050] The first component obtained in the classification step has a relatively high purity and is suitable for use as an aggregate, and therefore 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 step has a relatively low purity because it contains ash, etc. Therefore, the second component can be used as a raw material for general-purpose refractories, such as monolithic refractories, which require a relatively low level of purity.

[0052] In addition, in the classification step, the recycled refractory raw material may be classified into a plurality of classes. In this case, the recycled refractory raw material is obtained classified into predetermined particle size classes, and therefore, when the recycled refractory raw material is used as a refractory raw material, it becomes easier to use it according to the purpose. [Example]

[0053] Examples of the present invention will be described below. First, an experiment was conducted in which used magnesia-carbonaceous carbon-containing refractory bricks were refined and the resulting refined bricks were roasted in a fluidized bed roasting furnace, and the following items were measured.

[0054] (Sky speed) The superficial velocity was measured by installing a differential pressure flow meter at the nozzle through which gas was introduced from the blower into the furnace, and calculated by dividing the volumetric flow velocity under standard conditions by the cross-sectional area of ​​the column.

[0055] (carbon content) Free carbon (FC) was measured according to JIS R2011:2007.

[0056] (Experiment 1) The refined bricks were sieved, and the 5mm grain size bricks were charged into a fluidized bed roasting furnace for heat treatment. The charging rate was set at 0.57t / h, and the carbon content was measured by changing the heating temperature, heating time, and superficial velocity. Table 1 shows the carbon content. [Table 1]

[0057] (Experiment 2) As in Experiment 1, fine-grained bricks with a particle size of 5 mm were charged into a fluidized bed roasting furnace, and the heat treatment process was carried out at a heating temperature of 800°C, a heating time of 2 hours, and a superficial velocity of 1.5 m / s. Table 2 shows the carbon content when the amount of fine-grained brick charged under these conditions was changed. [Table 2]

[0058] In both Tables 1 and 2, the evaluation was conducted by rating samples with a carbon content of 1% by mass or less after treatment as "excellent," samples with a carbon content of more than 1% and 2% or less as "good," and samples with a carbon content of more than 2% by mass as "unacceptable."

[0059] In Examples 1 to 8 and Comparative Example in Table 1, the heating temperature, heating time, and superficial velocity were changed. In all of Examples 1 to 8, a regenerated refractory raw material with a sufficiently reduced carbon content was obtained. On the other hand, in Comparative Example, the carbon content was not sufficiently reduced. This is thought to be because in Comparative Example, the superficial velocity was set to 0 m / s, that is, no oxidizing gas was supplied to the fluidized roaster and no stirring was performed, resulting in insufficient stirring force, making it difficult for the composite particle aggregates to break down, and as a result, self-combustion of carbon was not promoted.

[0060] The amount of finely granulated bricks added was varied in Examples 9 to 11 in Table 2. In all cases, recycled refractory raw materials with sufficiently reduced carbon contents were obtained.

Claims

1. 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 granulated bricks; a heat treatment step of heating the granulated bricks while supplying an oxidizing gas into a fluidized roasting furnace.

2. 2. The method for producing a recycled refractory raw material according to claim 1, wherein the heating temperature in the heat treatment step is 700°C or higher and 900°C or lower.

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

4. 2. 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.

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

6. The method for producing a recycled refractory raw material according to claim 1, wherein the recycled refractory raw material has a carbon content of 2.0 mass% or less.

7. 7. 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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