The Influence of Carbon Anode Quality on Aluminum Electrolysis Production

As the heart of aluminum electrolysis cells, the quality and working condition of carbon anodes have a significant impact on whether aluminum electrolysis production is normal, as well as economic and technical indicators such as current efficiency, electrical energy consumption, and product grade.
1. Anode fault
70% of electrolytic cell failures occur at the anode. The common anode faults (symptoms) that occur in electrolytic cells include local overheating of the anode, uneven current distribution, anode falling off, anode "long package", anode crack fault, anode falling off, a large amount of carbon residue falling into the electrolyte, oxidation and combustion around the electrode, and anode tilting. These faults are mainly caused by quality issues with pre baked anodes and improper electrolysis operations.
(1) Anode detachment (decoupling). Due to poor casting of phosphorus pig iron or defects in the anode carbon bowl, the pre baked anode may experience detachment of the anode carbon block from the steel claw due to thermal expansion during use. When this phenomenon occurs, it is necessary to remove the carbon anode from the electrolytic cell and replace it with a new pre baked anode. When there are large cracks in the anode carbon block, it will also crack and fall off.
(2) Anode long package. Due to the uneven internal quality of the pre baked anode, the consumption rate of electrolysis is not synchronized during use, resulting in a local protrusion on the lower surface of the carbon anode, which is called the anode long package. If this phenomenon occurs, the anode needs to be removed, and after smashing the long package under the anode carbon block, the anode can continue to be used in the tank.
(3) Anode cracks. Pre baked anodes may sometimes have transverse or longitudinal cracks due to molding or roasting reasons. Generally speaking, anode carbon blocks with cracks found before anode casting are not cast; When cracks are found on the anode during use in the electrolytic cell, it is necessary to remove and replace it with a new pre baked anode.
The occurrence of a fault disrupts the normal production technical conditions of the electrolytic cell, resulting in disordered conditions of the electrolytic cell: voltage oscillation, voltage rise, aluminum water rolling, non crust on the electrolyte surface, partial non-conductivity and non operation of the electrolytic cell, causing a sharp decrease in current efficiency, a sharp increase in DC power consumption and raw material consumption, difficulties in electrolytic cell operation, a decrease in aluminum grade, and even leading to cell shutdown.
2. Impact on slot temperature and current distribution
The "acute symptoms" of various anode failures in aluminum electrolysis cells seriously affect the economic and technical indicators of the cells, as mentioned earlier. The chronic disease caused by poor anode quality leads to high temperature and uneven current distribution of the anode and electrolytic cell, which also seriously affects the economic and technical indicators of the aluminum electrolytic cell.
The current passing through aluminum electrolysis cells can reach tens to hundreds of kiloamperes, and changes in anode resistivity, anode conductive distance, and structural form strongly affect electrical energy consumption. The heat generated by the ohmic voltage drop of the anode is equivalent to a continuous operation of a 30-100KW electric donkey. The changes in the resistance of each part of the anode not only affect energy consumption, but also affect the working temperature of the anode and electrolytic cell, thus having a huge impact on current efficiency., If the resistivity of the carbon anode is increased by 75 μ Ω. m reduced to 50 μ Ω. m, tons of aluminum shell save 500KW. h. In addition, the carbon residue that falls into the electrolyte also affects current efficiency and power consumption. Research has shown that a carbon residue content of 0.04% in the electrolyte can reduce current efficiency by 1%; If the electrolyte contains 1% carbon residue, it can reduce the conductivity by 11%.
The oxidation reaction between carbon anode and air and carbon dioxide accounts for over 20% of the consumption of carbon anode. This reaction is selective and closely related to anode quality, anode process, electrolytic cell design, and electrolytic operation.
The reaction between carbon and air poses two major hazards to aluminum electrolysis cells. First, the reaction is a exothermic reaction, which causes the rise of anode bath temperature; The increase in temperature will accelerate the reaction during air circulation, forming a vicious cycle, which not only increases carbon consumption but also affects current efficiency; The second is the selective oxidation of this reaction, which causes a large amount of carbon slag to fall off, further endangering the technical and economic indicators of the electrolytic cell.