A carbon anode baking process for electrolytic aluminum

Abstract

The present invention discloses a carbon anode baking process for electrolytic aluminum, which comprises the following steps: calcined coke and coal tar pitch are proportioned in a suitable ratio and then placed in a kneader for kneading to obtain a paste; the paste is pressed and formed by a vibration molding machine to obtain a green body; the green body is placed in a microwave furnace cavity, and after the furnace cavity voids are filled with a filler, two-stage microwave frequency conversion baking is carried out; after the baked product is cooled to 50 °C, a sample is taken out and cooled to room temperature, and after the filler on the surface of the product is removed, a carbon anode for electrolytic aluminum is obtained. The present invention uses microwave heating to replace the traditional heating method, reduces the baking temperature and shortens the baking time, saves the non-renewable resources consumed in the traditional process, and reduces the production cost. The carbon anode for aluminum prepared by the present invention has better properties in all aspects than the commercially available carbon anode for aluminum.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon product preparation and aluminum electrolysis production, and in particular to a process for roasting carbon anodes for electrolytic aluminum, specifically a process for preparing carbon anodes for electrolytic aluminum by microwave roasting. Background Art

[0002] Carbon anodes are a crucial component of aluminum electrolytic cells, and their quality directly impacts the normal operation and various technical indicators of the aluminum industry. Carbon anodes are made from carbon aggregate (calcined coke and anode scrap) and a binder (coal tar pitch) through a series of processes, including mixing, forming, and calcining. Calcination involves heat-treating the pressed carbon blocks (green bodies) in an airtight environment at a specific temperature ramp rate to transform the coal tar pitch into coke. Calcination is a key heat treatment process that influences the physical and chemical properties of carbon anodes. During calcination, the coal tar pitch undergoes decomposition, cyclization, aromatization, and polycondensation, altering physical properties such as bulk density, true density, porosity, mechanical strength, and electrical conductivity. Current carbon anode production requires a complex temperature ramp due to heat transfer from the equipment to the green bodies and the coking reaction of the coal tar pitch. The maximum calcination temperature is around 1200°C, and the calcination cycle exceeds 20 hours. Furthermore, uneven heating often results in cracks, warping, and deformation in the products. Traditional roasting processes consume significant amounts of non-renewable energy. Heating is achieved through radiation or conduction, resulting in a heat utilization efficiency of only around 20%. Furthermore, uneven heating increases the roasting reject rate. Therefore, developing an efficient and clean process for roasting carbon anodes for electrolytic aluminum production is urgently needed.

[0003] Microwaves are electromagnetic waves with frequencies between 300MHz and 300GHz. Microwaves are characterized by short wavelength, high frequency, and strong penetrating properties. The primary principle of microwave heating is to utilize the rotation of polar molecules in an electromagnetic field to convert microwave energy into heat. When microwaves act on a medium, they penetrate deeply, heating the material both internally and externally simultaneously. This is a significant advantage of microwave heating over traditional heating methods. Currently, microwave heating technology is being applied to varying degrees in food drying, mineral metallurgy, energy and chemical engineering, and material preparation. Utilizing microwave heating technology to develop a new process for carbon anode roasting could overcome the current high energy consumption and cost constraints of this process.

[0004] The present invention is made in order to solve the above problems that are prevalent in the art.

[0005] The foregoing discussion of the background art is intended only to facilitate an understanding of the present invention. This discussion does not acknowledge or admit that any of the material referred to is part of the common general knowledge. Summary of the Invention

[0006] The object of the present invention is to propose a carbon anode baking process for electrolytic aluminum in view of the current deficiencies.

[0007] A carbon anode baking process for electrolytic aluminum includes the following steps:

[0008] S1. Mix calcined coke and coal tar pitch in a suitable proportion and place them in a kneader for kneading to obtain a paste. Use a vibrating molding machine to press the paste into blocks to obtain green bodies. Place the green bodies in a microwave furnace cavity, fill the furnace cavity gaps with a filler, and then perform two-stage microwave frequency conversion baking. After the baked product is cooled to 50 °C, take out the sample and cool it to room temperature. After removing the filler on the surface of the product, a carbon anode for electrolytic aluminum is obtained.

[0009] Preferably, in S1, the mass ratio of the calcined coke is 84 - 86 wt.%.

[0010] Preferably, in S1, the particle size distribution of the calcined coke is as follows: particles with a particle size of 6 - 12 mm account for 14 - 19% of the total particle mass, particles with a particle size of 3 - 6 mm account for 8 - 10%, particles with a particle size of 0.074 - 3 mm account for 45 - 55%, and particles with a particle size of -0.074 mm account for 22 - 24%.

[0011] Preferably, in S1, the mass ratio of the coal tar pitch is 14 - 16 wt.%.

[0012] Preferably, in S1, the kneading temperature is 170 - 180 °C and the time is 30 - 60 min.

[0013] Preferably, in S1, the filler is one of quartz sand, metallurgical coke, activated carbon, and carbon black.

[0014] More preferably, the filler is quartz sand.

[0015] The functions of the filler used are: one is to isolate air and prevent the green body from being oxidized during the baking process; the other is to adsorb the volatile gas and other flue gases discharged from the green body during the baking process.

[0016] Preferably, in S1, the microwave frequency of the first-stage baking is 2400 - 2500 MHz.

[0017] More preferably, the microwave frequency of the first-stage baking is 2450 MHz.

[0018] The half wavelength of the microwave at this frequency is approximately the diameter of small molecule components such as volatile components in coal tar pitch, which can cause more obvious resonance of small molecule components and extremely quickly change polarity, so as to better absorb energy and increase temperature to participate in the reaction.

[0019] Preferably, in S1, the temperature of the first-stage baking is 450 - 650 °C.

[0020] More preferably, the temperature of the first-stage roasting is 550 °C.

[0021] Under the environment of microwave heating, there is no obvious temperature gradient in each part of the substance. At this temperature, each part of the green body has completed reactions such as moisture volatilization, volatile removal, and formation of coal tar pitch semicoke. Compared with the traditional process, the roasting temperature is significantly reduced.

[0022] Preferably, the microwave heating time for the second-stage roasting in S1 is 2-4 h.

[0023] More preferably, the microwave heating time for the second-stage roasting is 4 h.

[0024] Preferably, the microwave frequency for the second-stage roasting in S1 is 865-965 MHz.

[0025] More preferably, the microwave frequency for the second-stage roasting is 915 MHz.

[0026] The half wavelength of the microwave at this frequency is approximately the diameter of macromolecular components such as polycyclic aromatic hydrocarbons, which can cause more obvious resonance in macromolecular components and extremely quickly change the polarity, so as to better absorb energy, increase temperature and participate in the reaction.

[0027] Preferably, the temperature of the second-stage roasting in S1 is 800-1000 °C.

[0028] More preferably, the temperature of the second-stage roasting is 900 °C.

[0029] Under the environment of microwave heating, there is no obvious temperature gradient in each part of the substance, and the heating is uniform. At this temperature, each part of the green body has completed the coal tar pitch coking reaction, volume shrinkage and physical property changes. Compared with the traditional process, the roasting temperature is reduced, and the cracks caused by uneven heating are significantly reduced.

[0030] Preferably, the microwave heating time for the second-stage roasting in S1 is 8-10 h.

[0031] More preferably, the microwave heating time for the second-stage roasting is 10 h.

[0032] Since the microwave effect occurs simultaneously inside and outside the substance and does not require a slow heat transfer process, there is no need to design a multi-stage heating process, which significantly shortens the roasting time.

[0033] The beneficial effects achieved by the present invention are:

[0034] 1. The present invention uses microwave heating to replace the traditional heating method, reducing the roasting temperature and shortening the roasting time, saving the non-renewable resources consumed in the traditional process, and reducing the production cost.

[0035] 2. During the microwave roasting process of the present invention, each part of the green body can be heated simultaneously and evenly, eliminating the need to design multi-stage heating steps and significantly reducing the generation of cracks.

[0036] 3. The present invention adopts two-stage microwave frequency conversion roasting. First, high frequency is used to enhance the reaction of small molecule components, and then low frequency is used to enhance the reaction of large molecule components, enabling the full optimization of physical and chemical properties during the roasting process.

[0037] 4. The physical and chemical properties such as mechanical strength, resistivity, and bulk density of the carbon anode for electrolytic aluminum obtained by the present invention are superior to those of commercially available carbon anodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention can be further understood from the following description in conjunction with the drawings.

[0039] Figure 1 It is a scanning electron microscope micrograph of the product obtained by the present invention.

[0040] Figure 2 It is a scanning electron microscope micrograph of the product obtained by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with its embodiments. It should be noted that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present case. For those skilled in the art, after referring to the following detailed description, other systems, methods, and / or features of this embodiment will become obvious. And the terms used to describe the positional relationship in the drawings are only for illustrative purposes and cannot be construed as a limitation of this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0042] Example 1:

[0043] Take 8.4 kg of calcined coke produced by a domestic factory. The particle size distribution of the calcined coke is as follows: particles with a particle size of 6 - 12 mm account for 15% of the total particle mass, particles with a particle size of 3 - 6 mm account for 9%, particles with a particle size of 0.074 - 3 mm account for 52%, and particles with a particle size of -0.074 mm account for 24%. Then mix in 1.6 kg of coal tar pitch produced by a domestic factory, put it into a kneader and knead at 180 °C for 60 min to obtain a paste, and then use a vibration molding machine to press the paste into blocks to obtain green bodies. Place the green bodies in the microwave furnace cavity, fill the furnace cavity gaps with quartz sand filler, and then carry out two-stage microwave frequency conversion roasting. The first-stage microwave frequency is 2450 MHz, the roasting temperature is 550 °C, and the treatment time is 4 h. The second-stage microwave frequency is 915 MHz, the roasting temperature is 900 °C, and the treatment time is 10 h. After roasting is completed, wait for the product to cool to 50 °C, take out the product and cool it to room temperature, and remove the filler on the surface of the product to obtain a carbon anode for electrolytic aluminum.

[0044] The bulk density of the obtained carbon anode for aluminum is 1.68 g / cm 3 , the resistivity is 50.2 μΩ·m, and the compressive strength is 53.6 MPa.

[0045] Example 2: This example is a further description of the above example. It should be understood that this example includes all the above technical features and makes a further specific description:

[0046] Take 17 kg of calcined coke produced by a domestic factory. The particle size distribution of the calcined coke is as follows: particles with a particle size of 6 - 12 mm account for 15% of the total particle mass, particles with a particle size of 3 - 6 mm account for 9%, particles with a particle size of 0.074 - 3 mm account for 52%, and particles with a particle size of -0.074 mm account for 24%. Then mix in 3 kg of coal tar pitch produced by a domestic factory, put it into a kneader and knead at 175 °C for 45 min to obtain a paste, and then use a vibration molding machine to press the paste into blocks to obtain green bodies. Place the green bodies in the microwave furnace cavity, fill the furnace cavity gaps with quartz sand filler, and then carry out two-stage microwave frequency conversion roasting. The first-stage microwave frequency is 2400 MHz, the roasting temperature is 500 °C, and the treatment time is 3 h. The second-stage microwave frequency is 900 MHz, the roasting temperature is 850 °C, and the treatment time is 9 h. After roasting is completed, wait for the product to cool to 50 °C, take out the product and cool it to room temperature, and remove the filler on the surface of the product to obtain a carbon anode for electrolytic aluminum.

[0047] The bulk density of the obtained carbon anode for aluminum is 1.65 g / cm 3 , the resistivity is 53.4 μΩ·m, and the compressive strength is 51.9 MPa.

[0048] Example 3: This example is a further description of the above example. It should be understood that this example includes all the above technical features and makes a further specific description:

[0049] Take 8.6 kg of calcined coke produced by a domestic factory. The particle size distribution of the calcined coke is as follows: particles with a particle size of 6 - 12 mm account for 15% of the total particle mass, particles with a particle size of 3 - 6 mm account for 9%, particles with a particle size of 0.074 - 3 mm account for 52%, and particles with a particle size of -0.074 mm account for 24%. Then mix in 1.4 kg of coal tar pitch produced by a domestic factory, put it into a kneader and knead at 170 °C for 30 min to obtain a paste, and then use a vibration molding machine to press and form the paste into a green body. Place the green body in the microwave furnace cavity, fill the furnace cavity gap with quartz sand filler, and then carry out two-stage microwave frequency conversion roasting. The first-stage microwave frequency is 2500 MHz, the roasting temperature is 600 °C, and the treatment time is 2 h. The second-stage microwave frequency is 965 MHz, the roasting temperature is 1000 °C, and the treatment time is 8 h. After roasting is completed, wait for the product to cool to 50 °C, take out the product and cool it to room temperature, and remove the filler on the surface of the product to obtain a carbon anode for electrolytic aluminum.

[0050] The bulk density of the obtained carbon anode for aluminum is 1.61 g / cm 3 , the resistivity is 54.7 μΩ·m, and the compressive strength is 50.4 MPa.

[0051] Compare the performance of the carbon anode obtained in the above example with the carbon anode produced by a certain carbon factory, and the results are shown in Table 1.

[0052] Table 1 Physical and chemical properties of various carbon anodes

[0053]

[0054] Result analysis: From the data comparison of the examples, the bulk density, resistivity, and mechanical strength of the carbon anodes obtained in Examples 1, 2, and 3 are all better than those of the carbon anodes for aluminum on the market. It can be seen that microwave frequency conversion roasting can reduce the roasting temperature and shorten the roasting time while improving the physical and chemical properties of the carbon anode.

[0055] In summary, for the roasting process of the carbon anode for electrolytic aluminum of the present invention, using microwave heating instead of the traditional heating method reduces the roasting temperature and shortens the roasting time, saves the non-renewable resources consumed in the traditional process, and reduces the production cost; during the microwave roasting process, each part of the green body can be heated simultaneously and evenly, without the need to design multi-stage heating steps, and significantly reduces the generation of cracks; adopting two-stage microwave frequency conversion roasting, first strengthening the reaction of small molecule components at a high frequency and then strengthening the reaction of large molecule components at a low frequency, enabling the full optimization of the physical and chemical properties during the roasting process; the physical and chemical properties such as the mechanical strength, resistivity, and bulk density of the obtained carbon anode for electrolytic aluminum are better than those of the commercially available carbon anodes.

[0056] Although the present invention has been described above with reference to various embodiments, it should be understood that many changes and modifications can be made without departing from the scope of the present invention. That is to say, the methods, systems and devices discussed above are examples. Various configurations can be appropriately omitted, replaced or various processes or components added. For example, in an alternative configuration, the method can be performed in an order different from the described order, and / or various components can be added, omitted and / or combined. Moreover, the features described with respect to certain configurations can be combined in various other configurations, such as different aspects and elements of the configurations can be combined in a similar manner. In addition, as technology develops, the elements therein can be updated, that is, many elements are examples and do not limit the scope of the present disclosure or the claims. And it should be understood that after reading the content described in the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A carbon anode baking process for electrolytic aluminum, characterized in that, It includes the following steps: Mix calcined coke and coal tar pitch in a suitable proportion and place them in a kneader to knead at 170 - 180 °C for 30 - 60 min to obtain a paste. Use a vibration molding machine to press the paste into blocks to obtain green bodies. Place the green bodies in a microwave furnace cavity, fill the furnace cavity gaps with a filler, and then carry out two-stage microwave frequency conversion roasting. After the roasted product is cooled to 50 °C, take out the sample and cool it to room temperature. After removing the filler on the surface of the product, a carbon anode for electrolytic aluminum is obtained; The particle size distribution of the calcined coke is as follows: particles with a particle size of 6 - 12 mm account for 14 - 19% of the total particle mass, particles with a particle size of 3 - 6 mm account for 8 - 10%, particles with a particle size of 0.074 - 3 mm account for 45 - 55%, and particles with a particle size of -0.074 mm account for 22 - 24%; the microwave frequency of the first stage of frequency conversion roasting is 2400 - 2500 MHz, the roasting temperature is 450 - 650 °C, the treatment time is 2 - 4 h, the microwave frequency of the second stage is 865 - 965 MHz, the roasting temperature is 800 - 1000 °C, and the treatment time is 8 - 10 h.

2. The carbon anode baking process for electrolytic aluminum according to claim 1, characterized in that, The mass ratio of the calcined coke is 84 - 86 wt.%, and the particle size distribution is as follows: particles with a particle size of 6 - 12 mm account for 15% of the total particle mass, particles with a particle size of 3 - 6 mm account for 9%, particles with a particle size of 0.074 - 3 mm account for 52%, and particles with a particle size of -0.074 mm account for 24%.

3. The carbon anode baking process for electrolytic aluminum according to claim 1, characterized in that, The mass ratio of the coal tar pitch is 14 - 16 wt.%.

4. The carbon anode baking process for electrolytic aluminum according to claim 1, characterized in that The kneading temperature is 180 °C and the time is 60 min.

5. The carbon anode baking process for electrolytic aluminum according to claim 1, characterized in that, The filler is one of quartz sand, metallurgical coke, activated carbon, and carbon black.

6. The carbon anode baking process for electrolytic aluminum according to claim 1, characterized in that, The microwave frequency of the first stage of roasting is 2450 MHz, the roasting temperature is 550 °C, and the roasting time is 4 h.

7. The carbon anode baking process for electrolytic aluminum according to claim 1, characterized in that, The microwave frequency of the second stage of roasting is 915 MHz, the roasting temperature is 900 °C, and the roasting time is 10 h.

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