CN118621381A - A high-quality prebaked anode and its preparation method - Google Patents

Abstract

The invention provides a high-quality prebaked anode and a preparation method thereof, which utilize auxiliary materials in a negative graphitization furnace as powder materials in the particle composition of the prebaked anode and provide a preparation method capable of effectively reducing the resistivity of the prebaked anode, reducing the air reactivity of the prebaked anode and reducing the CO2 reactivity of the prebaked anode.

Description

A high-quality prebaked anode and preparation method thereof

Technical Field

The invention belongs to the technical field of aluminum electrolysis and relates to a high-quality prebaked anode and a preparation method thereof.

Background Art

my country's electrolytic aluminum output in 2020 was 37.124 million tons. According to the calculation that the production of one ton of electrolytic aluminum consumes about 13,500 kWh of electricity, the total power consumption of the industry is about 501.174 billion kWh, accounting for 6.67% of my country's total social electricity consumption of 751.1 billion kWh in 2020. The carbon dioxide emitted by producing one ton of electrolytic aluminum in the electrolysis process is about 1.8 tons. At present, my country's prebaked anode production capacity is more than 30 million tons. In 2020, the total carbon dioxide emissions of the electrolytic aluminum industry are about 426 million tons, accounting for about 5% of the total net carbon dioxide emissions in the whole society.

As for the overall production status of electrolytic aluminum in China, the comprehensive energy utilization efficiency is about 15% lower than the international advanced level, which is mainly manifested in: the current efficiency is 2-3% different, the power consumption per ton of aluminum is 300-800Kwh different, and the consumption of electrolytic aluminum anode is 30-60Kg different (equivalent to about 75-150Kg of standard coal). These problems are mainly caused by the quality of carbon anodes for aluminum in my country.

The quality of carbon anode, such as the CO2/air reaction activity and resistivity of prebaked anode, directly or indirectly affects various economic and technical indicators of lead electrolysis, such as current efficiency, power consumption, anode carbon consumption, etc.

During the electrolysis process, the carbon anode with CO2/air reactivity of the prebaked anode will react with air and carbon dioxide at the same time as the anode reaction, and will be corroded by them. This will not only increase the consumption of the anode, but also cause the anode to slag. Therefore, reducing the air and carbon dioxide reactivity of the carbon anode is conducive to improving the current efficiency and reducing the carbon consumption and electricity consumption per ton of aluminum. The anode resistivity is a very direct standard for evaluating the quality of the anode, which directly affects the economic and technical indicators such as the electricity consumption per ton of aluminum and the cell voltage drop in aluminum electrolysis production.

The preparation process of prebaked anode includes the following five parts: preparation and sintering of raw materials, crushing and screening of calcined materials, batching and kneading, green block forming, and green block roasting. Reasonable particle grading determines the key anode properties such as prebaked anode density, thermal expansion coefficient and chemical reactivity. Batching is to mix forged coke particle aggregates of different particle sizes and petroleum coke powder in a certain proportion. The purpose is to obtain carbon materials with high bulk density and low porosity. The particle grading of carbon anode is generally made of 3-4 kinds of particle sizes of calcined coke: coarse particles, medium particles, small particles and powder. Large particles are piled up, medium particles are filled, and small particles and powder are further filled. The binder coal tar bonds the above components into a whole, and each component has its own special role.

The powder in the particle grading is filled in the gaps and pores between large particles, medium particles, and small particles. The increase in the appropriate powder ratio will increase the anode density, reduce the anode porosity, and improve the mechanical strength. At the same time, it will also make the anode appearance more delicate and smooth. However, if the powder is excessive, it will cause excessive internal stress inside the anode, causing cracks in the anode green block during sintering, reducing the strength of the pre-baked anode, increasing the resistivity, and increasing the CO2/air reaction.

At present, the powder in the prebaked anode particle grading generally only accounts for about 30%wt of the total dry material mass. The powder is calcined coke ball mill powder, dust removal and recovery powder, and the particle size is less than 75μm. These powders have a large specific surface area due to their small particle size; at the same time, the surface bond force unsaturated particles of the powder particles increase, and the active sites are generally considered to be mainly located at the edge sites and surfaces of the powder particles. The surface free energy is large, and the reaction activation energy of the system is reduced, that is, the reaction activity is improved. The kinetic mechanism of the reaction of prebaked anode carbon blocks with O2 and CO2 is a diffusion-controlled process. On the one hand, the large specific surface area and large surface free energy of the powder will promote the reactivity of the prebaked anode carbon blocks with O2 and CO2. During the aluminum electrolysis process, the carbon consumption and CO2 emissions of the prebaked anode increase; on the other hand, the powder obtained by crushing the calcined coke has a larger degree of crystal amorphization and an increased powder resistivity, which directly affects the economic and technical indicators such as the power consumption per ton of aluminum and the cell voltage drop in aluminum electrolysis production. Furthermore, in order to reduce production costs, some prebaked anode manufacturers add some dust removal powder to the prebaked anode particle grading powder. The particle size of these dust removal powders is generally less than 20μm, and the powder has a larger specific surface area; and the dust removal powder has less open macro porosity for coal tar pitch penetration. This reduces the ability of coal tar pitch to interlock and bond with its structure during carbonization and roasting. Prebaked anodes prepared from these calcined coke powder and dust removal powder materials are more prone to thermal shock cracking during the rapid heating process of aluminum electrolytic cells, resulting in serious "slag falling" and affecting the normal operation of aluminum electrolytic cells.

It is increasingly difficult for prebaked anode manufacturers to purchase suitable anode grade green petroleum coke at reasonable prices. The metal impurities and sulfur content in prebaked anode grade green petroleum coke are high. In the aluminum electrolysis process, the current status of prebaked anode raw materials inevitably leads to high air/CO2 reactivity of prebaked anode carbon blocks, increased carbon consumption, increased CO2 emissions, and low current efficiency.

At present, in order to reduce the CO2/air reaction activity of the prebaked anode, the main methods used are to add AlF3, Al2O3 antioxidants, or use the prebaked anode anti-oxidation coating method; to reduce the resistivity of the prebaked anode, the main method is to add graphite powder. Practice has shown that these methods have limited effects.

Technological innovation in the aluminum industry must adhere to green and low-carbon emission reduction and environmental protection bottom lines, and actively implement the "carbon peak and carbon neutrality" goals. In electrolytic aluminum production, it is necessary to effectively reduce the resistivity of the anode carbon blocks, reduce the air/CO2 reactivity of the anode carbon blocks, reduce the consumption of carbon anodes, reduce CO2 emissions, and improve current efficiency.

Glossary: Coal tar pitch is classified into low-temperature coal tar pitch, medium-temperature coal tar pitch and modified coal tar pitch according to the softening point. Among them, modified coal tar pitch has the following characteristics: softening point: 103-125℃, ash content: ≤0.3%, coking value: ≥56%, volatile matter: 48-54%, carbon: ≥50%, toluene insoluble matter: 28-32%, quinoline insoluble matter: 4-10%. It is generally used in: graphite electrodes, carbon products, graphite crucibles, prebaked anodes, aluminum plants, etc. Modified coal tar pitch, also known as coal tar pitch, is the product of coal tar after high-temperature distillation and debenzenization.

Summary of the invention

Based on the above background status, in order to solve the above technical problems, the present invention utilizes the auxiliary materials in the negative electrode graphitization furnace as the powder in the prebaked anode particle grading, and provides a prebaked anode and a preparation method thereof that can effectively reduce the reactivity of the anode carbon block to air and CO2 and reduce the resistivity of the prebaked anode.

The technical problem to be solved by the present invention is achieved through the following technical solutions:

The technical solutions adopted are:

A high-quality prebaked anode, wherein the mass ratio of the prebaked anode aggregate and the binder is 84:16; the prebaked anode aggregate comprises calcined petroleum coke>12mm, calcined petroleum coke 12-6mm, calcined petroleum coke 6-3mm, calcined petroleum coke powder <0.075mm, and graphitization furnace auxiliary material <0.075mm.

As a further improvement, the prebaked anode aggregate comprises 8wt%>12mm calcined petroleum coke, 12wt%12-6mm calcined petroleum coke, 40-55wt%6-3mm calcined petroleum coke, and 25-40wt%<0.075mm graphitization furnace auxiliary materials.

As a further improvement, the prebaked anode aggregate comprises 8wt% of calcined petroleum coke >12mm, 12wt% of calcined petroleum coke 12-6mm, 40wt% of calcined petroleum coke 6-3mm, 0-35wt% of calcined petroleum coke powder <0.075mm, and 5-40wt% of graphitization furnace auxiliary materials <0.075mm.

As a further improvement, in the graphitization furnace auxiliary material <0.075 mm, the purity of powder with a particle size less than 75 μm is ≥60%, and the purity of powder with a particle size less than 38 μm is ≤40%.

A further improvement is that the graphitization furnace auxiliary material is one of a graphitization furnace covering material and a graphitization furnace resistor material; the raw material of the graphitization furnace resistor material is a filler for the gaps between carbon products and between carbon products and furnace walls when the graphitization furnace is loaded, and the filler is calcined petroleum coke. After the carbon product is graphitized, the filler is the graphitization furnace resistor material; the raw material of the graphitization furnace covering material is a 150-200mm thick calcined petroleum coke laid on the top of the carbon product when the graphitization furnace is loaded, and after the carbon product is graphitized, the calcined petroleum coke is the graphitization furnace covering material.

As a further improvement, the binder is molten modified coal tar.

A method for preparing a high-quality prebaked anode comprises the following steps: adding prebaked anode aggregate into a kneading machine and kneading for 10 minutes, then adding modified coal tar pitch and kneading for 20 minutes, the kneading temperature is 170-175°C, to prepare a paste, the paste is molded by compression molding: the molding temperature is 145°C, the molding pressure is 50MPa, and the pressure holding time is 1min to prepare a prebaked anode green body, the prebaked anode green body is placed in a roasting furnace, baked, cooled and taken out of the furnace to obtain the high-quality prebaked anode, wherein the prebaked anode aggregate comprises calcined petroleum coke>12mm, calcined petroleum coke 12-6mm, calcined petroleum coke 6-3mm, calcined petroleum coke powder <0.075mm, and graphitization furnace auxiliary material <0.075mm.

As a further improvement, the calcination method is to heat the temperature from room temperature to 150°C at a heating rate of 100°C/h, then to 300°C at a heating rate of 10°C/h, and then to 1100°C at a heating rate of 50°C/h, keep the temperature for 20 hours, and then cool naturally.

As a further improvement, the prebaked anode aggregate comprises 8wt% of calcined petroleum coke >12mm, 12wt% of calcined petroleum coke 12-6mm, 40wt% of calcined petroleum coke 6-3mm, 0-35wt% of calcined petroleum coke powder <0.075mm, and 5-40wt% of graphitization furnace auxiliary materials <0.075mm.

As a further improvement, the graphitization furnace auxiliary material is one of a graphitization furnace covering material and a graphitization furnace resistor material, and the binder is modified coal tar.

The beneficial effects of the present invention are:

The high-quality prebaked anode of the present invention can effectively reduce the air/CO2 reactivity of the anode carbon block, reduce the resistivity of the prebaked anode, reduce the consumption of the carbon anode, reduce CO2 emissions, and improve current efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the XRD diagram of petroleum coke and graphitization furnace auxiliary materials of the present invention.

FIG. 2a is a TG/DTG diagram of calcined petroleum coke in the present invention.

FIG. 2 b is a TG/DTG diagram of the graphitization furnace covering material in the present invention.

FIG. 2c is a TG/DTG diagram of the graphitization furnace resistor material in the present invention.

FIG. 3 is a sintering temperature curve of the prebaked anode in the present invention.

DETAILED DESCRIPTION

The present invention is further described below by means of specific examples, but the present invention is not limited thereto, and the specific protection scope is shown in the claims.

In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose, the following is a detailed description of a method for preparing a high-quality prebaked anode according to the present invention in conjunction with the accompanying drawings and embodiments:

The invention comprises prebaked anode aggregate and a binder, and the prebaked anode aggregate and the binder are mixed and stirred to form a paste. The prebaked anode aggregate adopts four particle size ratios: >12mm calcined petroleum coke (8wt%), 12-6mm calcined petroleum coke (12wt%), 6-3mm calcined petroleum coke (40-55wt%), <0.075mm graphitization furnace auxiliary material (25-40wt%), the amount of prebaked anode aggregate is 84wt% of the total weight of the paste; the amount of coal tar binder is 16wt% of the total weight of the paste, and the softening point of the modified coal tar is 105°C.

840 g of aggregates in four-size proportions were added into a kneader and kneaded for 10 minutes, and then 160 g of modified coal tar was added and kneaded for 20 minutes at a kneading temperature of 170-175° C. to prepare the paste.

The paste was molded by compression molding: molding temperature: 145° C., molding pressure: 50 MPa, holding time: 1 min, to prepare a pre-baked anode green body.

The anode green body is placed in a baking furnace and baked according to the baking temperature curve in FIG3 , and then cooled and taken out of the furnace to obtain a high-quality prebaked anode for aluminum electrolysis.

The material composition and specific gravity used in the embodiment are shown in Table 1:

Table 1 Graphitization furnace auxiliary materials and trace elements of calcined petroleum coke

Example 1

According to the method for preparing the prebaked anode for aluminum electrolysis, the prebaked anode aggregate adopts four particle size ratios: 8wt% of calcined petroleum coke with a particle size of >12mm, 12t% of calcined petroleum coke with a particle size of 12-6mm, 40wt% of calcined petroleum coke with a particle size of 6-3mm, 35wt% of calcined petroleum coke powder with a particle size of <0.075mm, and 5wt% of graphitized furnace resistor material with a particle size of <0.075mm. Among them, the purity of the powder with a particle size of less than 75μm is 60%, and the purity of the powder with a particle size of less than 38μm is 10%, thereby obtaining the prebaked anode y1.

Example 2

According to the method for preparing the prebaked anode for aluminum electrolysis, the prebaked anode aggregate adopts four particle size ratios: 8wt% of calcined petroleum coke with a particle size of >12mm, 12t% of calcined petroleum coke with a particle size of 12-6mm, 40wt% of calcined petroleum coke with a particle size of 6-3mm, 25wt% of calcined petroleum coke powder with a particle size of <0.075mm, and 15wt% of graphitized furnace resistor material with a particle size of <0.075mm. Among them, the purity of the powder with a particle size of less than 75μm is 60%, and the purity of the powder with a particle size of less than 38μm is 10%, thereby obtaining the prebaked anode y2.

Example 3

According to the method for preparing prebaked anodes for aluminum electrolysis, the prebaked anode aggregate adopts four particle size ratios: 8wt% of calcined petroleum coke with a particle size of >12mm, 12t% of calcined petroleum coke with a particle size of 12-6mm, 40wt% of calcined petroleum coke with a particle size of 6-3mm, 15wt% of calcined petroleum coke powder with a particle size of <0.075mm, and 25wt% of graphitized furnace resistor material with a particle size of <0.075mm. Among them, the purity of powder with a particle size of less than 75μm is 60%, and the purity of powder with a particle size of less than 38μm is 10%, thereby obtaining a prebaked anode y3.

Example 4

According to the preparation method of the prebaked anode for aluminum electrolysis, the prebaked anode aggregate adopts four particle size ratios: 8wt% of calcined petroleum coke>12mm, 12t% of calcined petroleum coke 12-6mm, 40wt% of calcined petroleum coke 6-3mm, 5wt% of calcined petroleum coke powder <0.075mm, and 35wt% of graphitized furnace resistor material <0.075mm. Among them, the purity of powder less than 75μm is 60%, and the purity of powder less than 38μm is 10%, and the prebaked anode y4 is obtained.

Example 5

According to the preparation method of the prebaked anode for aluminum electrolysis, the prebaked anode aggregate adopts four particle size ratios: 8wt% of calcined petroleum coke>12mm, 12t% of calcined petroleum coke 12-6mm, 40wt% of calcined petroleum coke 6-3mm, and 40wt% of graphitized furnace resistor material <0.075mm. Among them, the purity of powder less than 75μm is 60%, and the purity of powder less than 38μm is 10%, and the prebaked anode y5 is obtained.

Example 6

According to the preparation method of the prebaked anode for aluminum electrolysis, the prebaked anode aggregate adopts four particle size ratios: 8wt% of calcined petroleum coke>12mm, 12t% of calcined petroleum coke 12-6mm, 40wt% of calcined petroleum coke 6-3mm, 15wt% of calcined petroleum coke powder <0.075mm, and 25wt% of graphitization furnace covering material <0.075mm. Among them, the purity of powder less than 75μm is 60%, and the purity of powder less than 38μm is 10%, and the prebaked anode y6 is obtained.

Example 7

According to the preparation method of the prebaked anode for aluminum electrolysis, the prebaked anode aggregate adopts four particle size ratios: 8wt% of calcined petroleum coke>12mm, 12t% of calcined petroleum coke 12-6mm, 40wt% of calcined petroleum coke 6-3mm, 10wt% of calcined petroleum coke powder <0.075mm, and 30wt% of graphitization furnace covering material <0.075mm. Among them, the purity of powder less than 75μm is 60%, and the purity of powder less than 38μm is 10%, and the prebaked anode y7 is obtained.

Example 8

According to the preparation method of the prebaked anode for aluminum electrolysis, the prebaked anode aggregate adopts four particle size ratios: 8wt% of calcined petroleum coke>12mm, 12t% of calcined petroleum coke 12-6mm, 40wt% of calcined petroleum coke 6-3mm, 5wt% of calcined petroleum coke powder <0.075mm, and 35wt% of graphitization furnace covering material <0.075mm. Among them, the purity of powder less than 75μm is 60%, and the purity of powder less than 38μm is 10%, and the prebaked anode y8 is obtained.

Embodiment 9

According to the preparation method of the prebaked anode for aluminum electrolysis, the prebaked anode aggregate adopts four particle size ratios: 8wt% of calcined petroleum coke with a particle size of >12mm, 12t% of calcined petroleum coke with a particle size of 12-6mm, 40wt% of calcined petroleum coke with a particle size of 6-3mm, and 40wt% of graphitized furnace covering material with a particle size of <0.075mm. Among them, the purity of the powder less than 75μm is 60%, and the purity of the powder less than 38μm is 10%, thereby obtaining the prebaked anode y9.

Example 10 (comparative sample)

According to the method for preparing prebaked anodes for aluminum electrolysis, the prebaked anode aggregate adopts four particle size ratios: 8wt% of calcined petroleum coke with a particle size of >12mm, 12t% of calcined petroleum coke with a particle size of 12-6mm, 40wt% of calcined petroleum coke with a particle size of 6-3mm, and 40wt% of calcined petroleum coke powder with a particle size of <0.075mm. Among them, the purity of the powder with a particle size of less than 75μm is 60%, and the purity of the powder with a particle size of less than 38μm is 10%, thereby obtaining the prebaked anode y10.

The performance of the prebaked anodes y1 to y10 for anti-oxidation aluminum electrolysis was tested. The test results are shown in the following table:

From the performance test results of y1-y5, it can be seen that initially, with the increase of the amount of <0.075mm graphitization furnace resistor material, the resistivity of the prebaked anode decreases, the compressive strength increases, and the air-air reaction residual rate and CO2 reaction residual rate increase; however, when the amount of <0.075mm graphitization furnace resistor material is 40wt%, the resistivity of the prebaked anode increases, and the compressive strength, air-air reaction residual rate, and CO2 reaction residual rate decrease. Therefore, it is appropriate that the amount of <0.075mm graphitization furnace resistor material is ≤40wt%.

From the performance test results of y6-y9, it can be seen that with the increase of the amount of <0.075mm graphitization furnace covering material, the resistivity of the prebaked anode decreases, the compressive strength increases, and the air-air reaction residual rate and CO2 reaction residual rate increase; however, when the amount of <0.075mm graphitization furnace covering material is 40wt%, the resistivity of the prebaked anode increases, and the compressive strength, air-air reaction residual rate, and CO2 reaction residual rate decrease. Therefore, it is appropriate that the amount of <0.075mm graphitization furnace covering material is ≤40wt%.

As a comparison, the performance test results of y10 show that compared with the related technology, the prebaked anode of the present invention can effectively reduce its resistivity, reduce the air and CO2 reactivity of the anode carbon block in the electrolytic aluminum production, and can effectively reduce the consumption of carbon anode and reduce CO2 emissions.

The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, makes any simple modifications, equivalent changes and modifications to the above embodiments based on the technical essence of the present invention, which still fall within the scope of the technical solution of the present invention.

The series of detailed descriptions described above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Various changes made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present invention belong to the scope of protection of the present invention.

Claims (9)

1. A high-quality prebaked anode, characterized in that the mass ratio of the prebaked anode aggregate and the binder is 84:16; the prebaked anode aggregate includes calcined petroleum coke>12mm, calcined petroleum coke 12-6mm, calcined petroleum coke 6-3mm, calcined petroleum coke powder<0.075mm, and graphitization furnace auxiliary material<0.075mm. 2. The high-quality prebaked anode according to claim 1 is characterized in that the prebaked anode aggregate comprises 8wt% of calcined petroleum coke>12mm, 12wt% of calcined petroleum coke 12-6mm, 40wt% of calcined petroleum coke 6-3mm, 0-35wt% of calcined petroleum coke powder <0.075mm, and 5-40wt% of graphitization furnace auxiliary materials <0.075mm. 3. The high-quality prebaked anode according to claim 2 is characterized in that, in the graphitization furnace auxiliary materials <0.075 mm, the purity of the powder with a particle size less than 75 μm is ≥60%, and the purity of the powder with a particle size less than 38 μm is ≤40%. 4. The high-quality prebaked anode according to claim 1 is characterized in that the graphitization furnace auxiliary material is one of a graphitization furnace covering material and a graphitization furnace resistor material; the raw material of the graphitization furnace resistor material is a filler for the gaps between carbon products and between carbon products and furnace walls when the graphitization furnace is loaded, and the filler is calcined petroleum coke. After the carbon product is graphitized, the filler is the graphitization furnace resistor material; the raw material of the graphitization furnace covering material is a 150-200mm thick calcined petroleum coke on the top of the carbon product when the graphitization furnace is loaded, and after the carbon product is graphitized, the calcined petroleum coke is the graphitization furnace covering material. 5. The high-quality prebaked anode according to claim 1, characterized in that the binder is modified coal tar pitch. 6. A method for preparing a high-quality prebaked anode, characterized in that it comprises the following steps: adding prebaked anode aggregate to a kneader and kneading for 10 minutes, then adding modified coal tar pitch and kneading for 20 minutes, the kneading temperature is 170-175°C, to prepare a paste, the paste is molded by compression molding: molding temperature is 145°C, molding pressure is 50MPa, and holding time is 1min to prepare a prebaked anode green body, the prebaked anode green body is placed in a roasting furnace, roasted, and then cooled out of the furnace to obtain the high-quality prebaked anode, wherein the prebaked anode aggregate includes calcined petroleum coke>12mm, calcined petroleum coke 12-6mm, calcined petroleum coke 6-3mm, calcined petroleum coke powder <0.075mm, and graphitization furnace auxiliary material <0.075mm. 7. The method for preparing a high-quality prebaked anode as described in claim 6 is characterized in that the calcination method is to heat the temperature from room temperature to 150°C at a heating rate of 100°C/h, then to 300°C at a heating rate of 10°C/h, and then to 1100°C at a heating rate of 50°C/h, keep the temperature for 20 hours, and then cool naturally. 8. The method for preparing a high-quality prebaked anode according to claim 6, characterized in that the prebaked anode aggregate comprises 8wt%>12mm calcined petroleum coke, 12wt%12-6mm calcined petroleum coke, 40wt%6-3mm calcined petroleum coke, 0-35wt%<0.075mm calcined petroleum coke powder, and 5-40wt%<0.075mm graphitization furnace auxiliary materials. 9. The method for preparing a high-quality prebaked anode according to claim 6, characterized in that the graphitization furnace auxiliary material is one of a graphitization furnace covering material and a graphitization furnace resistor material, and the binder is modified coal tar pitch.