Carbon brick for Acheson graphitization furnace and preparation method thereof

Abstract

The invention discloses a carbon brick for an Acheson graphitization furnace and a preparation method of the carbon brick, and belongs to the technical field of graphitization furnace production. The raw materials for preparing the effective components of the carbon brick comprise the following components in parts by weight: 38-50 parts of coal with the particle size of 0.15-3mm, 15-27 parts of coal with the particle size of less than 0.15 mm, 2-8 parts of boric oxide, 2-8 parts of carbon black and 15-30 parts of a binder. Compared with a granular resistance material, the carbon brick disclosed by the invention is more compact and uniform in structure, and more uniform and stable in provided heat; and the resistance performance and the structure are stable, the repeated utilization rate is high, and the production cost is greatly reduced. The method is suitable for the Acheson graphitization furnace to produce graphitized materials.

Description

Technical Field

[0001] The invention belongs to the technical field of graphitization furnace production and relates to an Acheson graphitization furnace, in particular to a carbon brick for an Acheson graphitization furnace and a preparation method thereof. Background Art

[0002] A graphitization furnace is a device that converts amorphous carbon into a layered graphite structure with regular arrangement through high temperature. Acheson graphitization furnace is a type of graphitization furnace. Its prototype is: in a furnace body constructed of refractory materials, graphitized products and resistors are placed to form a conductive furnace core. The furnace core is surrounded by thermal insulation materials. The furnace head is equipped with conductive electrodes, which are connected to the power supply to form an energized circuit. When the circuit is connected, the furnace core heats up due to the action of the resistor, so that the graphitized products are graphitized at a high temperature of more than 2300℃. Among them, the role of the resistor is to increase the effective resistance of the furnace core and ensure uniform heat supply to the graphitized products. During the furnace loading process, the crucibles containing the graphitized products are first loaded into the furnace in layers, and then the resistors are filled between the crucibles, and the top is covered with insulation materials to form a complete filling structure.

[0003] At present, the commonly used resistor materials are mainly metallurgical coke, graphitized coke, and mixed coke of the two in different proportions. In actual production, with the increase of the effective resistance of the furnace core, the power factor of the graphitization furnace equipment also increases, which is more conducive to improving the productivity of the graphitization furnace and reducing power consumption. However, traditional resistor materials such as metallurgical coke, graphitized coke and mixed coke, especially metallurgical coke, have different degrees of high ash content, high sulfur content, low true density, high specific resistance, and large burnout (burnout of about 30%-40%). The problem requires continuous replenishment, which not only increases the production cost, but also limits the improvement of the effective resistance of the furnace core. The particle size of the resistor material affects the graphitization process. The small-particle resistor material can fill the gap, but the reuse rate is low and the contact resistance is large; while the large-particle resistor material has the advantages of recyclability and low contact resistance, but it is not filled solidly and heated unevenly during the graphitization process.

[0004] Although the technical route of the Acheson graphitization furnace is mature and highly operable, there are problems such as high cost of resistor materials, low recycling rate, large heat loss and non-reusability (the resistivity of the resistor material drops greatly after high-temperature graphitization, and it can no longer be used as a resistor material, but can only be sold as a by-product for comprehensive utilization). In actual production, multiple steps are required, such as laying the bottom material, surrounding the furnace core, putting the crucible into the furnace and filling the resistor material, etc. Each step requires precise control, which increases the difficulty of operation; a large amount of dust and noise will be generated in the process of loading the furnace and filling the resistor material. Although there are collection systems and bag dust collectors to deal with these dusts, they still have a negative impact on the environment and workers' health.

[0005] At present, the carbon bricks on the market are all carbon bricks suitable for blast furnaces. They have low resistivity and mainly play the role of thermal insulation. They are completely different from the role and requirements of Acheson graphitization furnace resistors. Therefore, they are not suitable for Acheson graphitization furnaces. There are currently no carbon bricks for Acheson graphitization furnaces on the market. Summary of the invention

[0006] The purpose of the present invention is to provide a carbon brick for an Acheson graphitization furnace and a preparation method thereof, so as to solve the problems of high cost, low recycling rate, large heat loss, environmental pollution, etc. of current resistor materials.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A carbon brick for an Acheson graphitization furnace. The raw materials of its effective components include, by weight, 38-50 parts of coal with a particle size of 0.15-3mm, 15-27 parts of coal with a particle size less than 0.15mm, 2-8 parts of boron oxide, 2-8 parts of carbon black and 15-30 parts of a binder.

[0009] As a limitation, the particle size of the boron oxide is 200 mesh, and the particle size of the carbon black is 325 mesh.

[0010] As another limitation, the coal includes electric calcined coal and / or ordinary calcined coal, and the binder includes asphalt.

[0011] As a further limitation, the asphalt is medium-temperature asphalt with a softening point of 80-95° C. and a coking value of ≥48%.

[0012] The present invention also provides a method for preparing the above-mentioned carbon brick for Acheson graphitization furnace, which comprises dry mixing coal, boron oxide and carbon black, adding a binder for wet mixing, vacuum molding and then baking to obtain the carbon brick for Acheson graphitization furnace.

[0013] As a limitation, the temperature of the dry mixing is ≥90°C and the time is 20-30 minutes; the temperature of the wet mixing is 150-160°C and the time is 30-40 minutes.

[0014] As another limitation, the vacuum molding has a vacuum degree of less than -0.08MPa, a pressure of 18-25MPa, and a time of 40-80s.

[0015] As a third limitation, the calcination has a heating rate of ≤10°C / min, a temperature of 800-1300°C, and a holding time of 48-72h.

[0016] Due to the adoption of the above technical solution, the present invention has the following technical advances compared with the prior art:

[0017] ① The carbon brick for an Acheson graphitization furnace provided by the present invention has a more compact and uniform structure compared to granular resistor materials, so the heat provided to the graphitized product through resistance heating is also more uniform and stable;

[0018] ② The carbon brick for Acheson graphitization furnace provided by the present invention has stable resistance performance and structure, high reuse rate, and can be reused ≥ 40 times. It can replace 50%-90% of granular resistor materials, which greatly reduces the production cost compared with the use of all non-recyclable granular resistor materials;

[0019] ③ In the carbon brick for Acheson graphitization furnace provided by the present invention, boron oxide keeps the carbon brick at a relatively low anisotropy, thereby maintaining the yield of the carbon brick during the molding and baking process, and also affects the conductivity of the carbon brick: when the boron oxide content is lower than 2wt%, the specific resistance is lower, the thermal expansion coefficient is higher, and the resistance heating efficiency is low during use; when the boron oxide content is higher than 8wt%, the cost increases, and the resistivity does not meet the use requirements; 2wt%-8wt% of boron oxide keeps the resistivity of the carbon brick at 110-200μΩ·m;

[0020] ④ The present invention provides a method for preparing carbon bricks for an Acheson graphitization furnace. The preparation process is simple and suitable for industrial production. The use of carbon bricks can reduce the steps of filling resistor materials and compacting operations in the Acheson graphitization furnace, significantly improve work efficiency, reduce dust generation, and reduce the use of collection systems and bag dust collectors. At the same time, it is friendly to the environment and workers' health. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below by specific examples. It should be understood that the described examples are only used to explain the present invention, and are not intended to limit the present invention.

[0022] Example 1

[0023] This embodiment prepares a carbon brick for an Acheson graphitization furnace and detects the relevant properties of the carbon brick, which specifically includes the following steps performed in sequence:

[0024] S1. Preparation of carbon bricks

[0025] Take 450kg of 3mm electric calcined coal, 252kg of 0.1mm electric calcined coal, 28kg of 200-mesh boron oxide (content 2.8wt%) and 50kg of 325-mesh carbon black for dry mixing for 20 minutes. After the dry mixing, the temperature of the dry material is 90°C. Then add 220kg of medium-temperature asphalt (softening point 80-95°C, coking value ≥48%) for wet mixing for 30 minutes. The paste temperature is 150°C. After the paste is put into the disc feeder, it is distributed into the mold through the distribution belt. The paste temperature in the mold is required to be in the range of 140-155°C. After the distribution is completed, the mold Enter the forming position, the vacuum cover falls and presses tightly, and vacuum is started for vacuum molding. The working vacuum degree is -0.09MPa. The pressure is maintained at 18MPa for 40s. After the pressing is completed, the pressure is released, the vacuum is removed, the upper punch is lifted, the top of the mold is loosened, the upper punch is lifted, the mold moves out of the forming position, reaches the demolding position, the carbon brick is ejected, and the carbon brick is pushed out. Then it is hoisted into the circulating cooling water pool for cooling for 4h. The water temperature of the brick is required not to exceed 50℃. The yield of vacuum molding is ≥96%. Then the green body is heated to 1300℃ at a heating rate of 10℃ / min and kept warm for 48h to obtain carbon brick ɑ1 for Acheson graphitization furnace.

[0026] S2. Performance Testing

[0027] Take carbon brick ɑ1 for Acheson graphitization furnace and test its performance. The method standards used for testing performance indicators are: GB / T 1429-2009 "Determination of ash content of carbon materials", GB / T 214-2007 "Determination of total sulfur in coal", GB / T 7320-2018 "Test method for thermal expansion of refractory materials" (using the ratio of vertical and parallel directions), GB / T 24525-2009 "Determination of resistivity of carbon materials", GB / T 1431-2019 "Determination of compressive strength of carbon materials";

[0028] The results of tests showed that the carbon brick had an ash content of 8.36%, a sulfur content of 0.02%, an anisotropy ratio of 1.7, a resistivity of 176.38 μΩ·m, and a compressive strength of 26.6 MPa, which met the use conditions of the graphitization furnace.

[0029] S3. Cycle times

[0030] The Acheson graphitization furnace carbon brick ɑ1 was placed under the graphitization temperature and repeatedly heated and cooled to simulate the use conditions of the graphitization furnace. After each cooling, the resistivity of the carbon brick was tested according to GB / T 24525-2009 "Determination of resistivity of carbon materials". The results are shown in Table 1:

[0031] Table 1 Resistivity list

[0032]

[0033] It can be seen from Table 1 that after multiple cycles of high-temperature use, the resistivity of the carbon brick gradually decreases. After the 42nd cycle, the resistivity drops to 108.61 μΩ·m, which no longer meets the resistivity requirements of carbon bricks for Acheson graphitization furnaces (110-200 μΩ·m), that is, the carbon brick can be reused 42 times.

[0034] Example 2

[0035] This embodiment prepares a carbon brick for an Acheson graphitization furnace, which specifically includes the following steps performed in sequence:

[0036] Take 500kg of common calcined coal with a particle size of 0.15mm, 270kg of common calcined coal with a particle size of 0.1mm, 80kg of 200-mesh boron oxide (content of 6.5wt%) and 80kg of 325-mesh carbon black for dry mixing for 30min. After the dry mixing, the temperature of the dry material is 100℃. Then add 300kg of medium-temperature asphalt (softening point of 80-95℃, coking value ≥48%) for wet mixing for 40min. The paste temperature is 160℃. After the paste is put into the disc feeder, it is distributed into the mold through the distribution belt. The paste temperature in the mold is required to be in the range of 140-155℃. The rear mold enters the forming position, the vacuum cover falls and presses, and vacuum is started for vacuum molding. The working vacuum degree is -0.09MPa, and the pressure is maintained at 25MPa for 80s. After the pressing is completed, the pressure is released, the vacuum is removed, the upper punch is lifted, the top of the mold is loosened, the upper punch is lifted, the mold moves out of the forming position, reaches the demolding position, the carbon brick is ejected, and the carbon brick is pushed out. Then it is hoisted into the circulating cooling water pool for cooling for 4h. The water temperature of the brick is required not to exceed 50℃. The yield of the vacuum molding is ≥96%. Then the green body is heated to 800℃ at a heating rate of 5℃ / min and kept warm for 72h to obtain carbon brick ɑ2 for Acheson graphitization furnace.

[0037] Example 3

[0038] This embodiment prepares a carbon brick for an Acheson graphitization furnace, which specifically includes the following steps performed in sequence:

[0039] Take 380kg of mixed coal with a mass ratio of 1:1 of ordinary calcined coal and electric calcined coal with a particle size of 2mm, 150kg of mixed coal with a particle size of 0.1mm, 20kg of 200-mesh boron oxide (content of 2.8wt%) and 20kg of 325-mesh carbon black for dry mixing for 25 minutes. After the dry mixing, the temperature of the dry material is 90°C, and then 150kg of medium-temperature asphalt (softening point of 80-95°C, coking value ≥48%) is added for wet mixing for 35 minutes. The paste temperature is 155°C. After the paste is put into the disc feeder, it is fed into the mold through the feeding belt. The paste temperature in the mold is required to be in the range of 140-155°C After the material is laid, the mold enters the forming position, the vacuum cover falls and presses, and vacuum is started for vacuum molding. The working vacuum degree is -0.09MPa, and the pressure is maintained at 20MPa for 60s. After the pressing is completed, the pressure is released, the vacuum is released, the upper punch is lifted, the top in the mold is loosened, the upper punch is lifted, the mold moves out of the forming position, reaches the demolding position, the carbon brick is ejected, and the carbon brick is pushed out, and then hoisted into the circulating cooling water pool for cooling for 4h. The water temperature of the brick is required not to exceed 50℃. The finished product rate of vacuum molding is ≥96%, and then the green body is heated to 1000℃ at a heating rate of 10℃ / min and kept warm for 60h to obtain carbon brick ɑ3 for Acheson graphitization furnace.

Claims

1. A carbon brick for an Acheson graphitization furnace, characterized in that: The raw materials for making its effective components include, by weight, 38-50 parts of coal with a particle size of 0.15-3mm, 15-27 parts of coal with a particle size less than 0.15mm, 2-8 parts of boron oxide, 2-8 parts of carbon black and 15-30 parts of a binder.

2. The carbon brick for Acheson graphitization furnace according to claim 1, characterized in that: The particle size of the boron oxide is 200 meshes, and the particle size of the carbon black is 325 meshes.

3. A carbon brick for an Acheson graphitization furnace according to claim 1 or 2, characterized in that: The coal includes electric calcined coal and / or ordinary calcined coal, and the binder includes asphalt.

4. The carbon brick for Acheson graphitization furnace according to claim 3, characterized in that: The asphalt is medium-temperature asphalt with a softening point of 80-95° C. and a coking value of ≥48%.

5. A method for preparing carbon bricks for an Acheson graphitization furnace according to any one of claims 1 to 4, characterized in that: The carbon bricks for the Acheson graphitization furnace are obtained by dry-mixing coal, boron oxide and carbon black, adding a binder for wet mixing, vacuum molding and then baking.

6. The method for preparing carbon bricks for Acheson graphitization furnace according to claim 5, characterized in that: The dry mixing is performed at a temperature of ≥90°C and a time of 20-30 minutes; the wet mixing is performed at a temperature of 150-160°C and a time of 30-40 minutes.

7. The method for preparing carbon bricks for Acheson graphitization furnace according to claim 5, characterized in that: The vacuum molding has a vacuum degree of less than -0.08MPa, a pressure of 18-25MPa, and a time of 40-80s.

8. A method for preparing carbon bricks for an Acheson graphitization furnace according to any one of claims 5 to 7, characterized in that: The calcination has a heating rate of ≤10°C / min, a temperature of 800-1300°C, and a heat preservation time of 48-72h.

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