What Is a Carbon Anode?

Carbon anode used in alu-minium electrolysis refers to the carbon electrode in the aluminum electrolytic cell that is connected to the positive electrode of the power supply. It includes a carbon anode body and a metal anode conductor. In the early development of the aluminum industry, small pre-baked anodes of thousands of amperes were used, which was compatible with the production level of the charcoal industry at that time. In order to increase the size of the anode to increase the current intensity, in the early 1920s, referring to the continuous self-baking electrode type of the ferroalloy electric furnace at that time, it was installed on the aluminum electrolytic cell, and the anode was continuously self-baked. In the 1940s, in order to simplify the anode operation and improve the degree of mechanization, the plug-in self-baked anode was developed. In the 1950s, due to the improvement of the quality of carbon electrodes and the success of large-scale pre-baked anode carbon blocks by vibration molding, pre-baked anodes were widely used. In the late 1980s, the current capacity of the latest pre-baked anode aluminum electrolytic cell has reached above 280-300kA.

Carbon anode used in alu-minium electrolysis refers to aluminum

During the aluminum electrolysis process, the average daily consumption of carbon anodes is about 2 cm. It is necessary to periodically add new anode paste (self-baked anode) to the electrolytic cell or replace the new anode block (pre-baked anode) regularly to keep the aluminum electrolytic cell running normally.

The basic requirements of aluminum anodes for carbon anodes are: resistance to molten salt erosion, lower resistance, higher purity, and better mechanical strength. The quality and working condition of carbon anode have a great influence on the efficiency of aluminum electrolysis current, power consumption and material consumption of aluminum electrolysis.

During normal operation of the aluminum electrolytic cell, the ohmic voltage drop of the carbon anode is 300-600mV, which accounts for 10% -15% of the cell voltage. The net consumption of a ton of aluminum-carbon anode is 400-500kg (based on residual electrode recovery). By improving the quality of raw materials, improving the production formula and process, the structure of the anode, and the working system of the anode, the quality of the anode can be improved. ^[2]

There are two types of continuous self-baked anodes (referred to as self-baked anodes) and pre-baked anodes.

Self-baked anode

The self-baking anode is to pyrolyze the pitch in the anode paste by using the heat of the aluminum electrolytic cell. After coking, it forms a dense solid anode with the carbon particles of the aggregate. Self-baked anodes are mostly monolithic single anodes, and are divided into side-inserted (or side-inserted) rod self-baked anodes and upper-inserted bar self-baked anodes according to the insertion method of conductive steel rods (anode bars).

2. Prebaked anode

The prebaked anode of the aluminum electrolytic cell is composed of a plurality of anode carbon blocks. Each anode carbon block group consists of 1-2 pieces of anode carbon blocks with a width of 700-900mm, a length of 1400-1700mm, and a height of 500-600mm, anode guide rods and steel claws. Cast iron or carbon paste to tamp the carbon block and steel claw together, the anode guide rod connected to the steel claw is pressed and fixed on the anode bus bar, and the anode lifting mechanism is used to lift the anode ^[3]

There are mainly two types of petroleum coke and coal tar. Petroleum coke is a chemical product of residue coke in petroleum processing. It contains 80% -95% carbon and 10% -20% volatiles and moisture. According to different coking methods, petroleum coke is divided into delayed petroleum coke, kettle petroleum coke, needle petroleum coke and fluidized petroleum coke. Delayed petroleum coke is the main raw material for making carbon anodes for aluminum electrolysis. Pitch coke formed by coal pitch coking is also an excellent raw material for making such anodes. Coal has been processed to remove ash instead of petroleum coke as a raw material for the production of carbon anodes for aluminum electrolysis ^[3]

It consists of calcining, crushing, batching and kneading, forming and roasting, and assembly operations ^[1] .