Effect of sulfur content on prebaked anode and calcination
Effect of sulfur content on prebaked anode and calcination
According to the level of sulfur content, petroleum coke can be divided into three types: sulfur content > 2.5% (also 3% or 2.8%) petroleum coke called high sulfur petroleum coke; Petroleum coke with 1% < sulfur content ≤2.5% is medium sulfur coke; Petro
According to the level of sulfur content, petroleum coke can be divided into three types: sulfur content > 2.5% (also 3% or 2.8%) petroleum coke called high sulfur petroleum coke; Petroleum coke with 1% < sulfur content ≤2.5% is medium sulfur coke; Petroleum coke with sulfur content ≤1% is called low sulfur coke.
According to the long-term planning of China's oil energy use, China will continue to increase the proportion of imported crude oil in the future, and crude oil with high sulfur content in the Middle East accounts for the majority, so the production of high sulfur coke will be higher and higher.
The high sulfur content of imported oil drives the rapid growth of the output of high-sulfur petroleum coke in China. In recent years, the share of high-sulfur crude oil in China's imported crude oil is increasing, and the proportion of high-sulfur petroleum coke is also increasing.
Harm of high sulfur petroleum coke to prebaked anode
When high sulfur coke is used to prepare pre-baked anode, most of the sulfur is transferred to the anode, and in the process of electrolysis, the sulfur in coke reacts with carbon to form carbon sulfur film, which leads to the increase of anode resistivity and the decrease of electrolysis efficiency.
The sulfur will react with the metal conductive steel claw of pre-baking anode at high temperature, and generate the iron sulfide film with high resistance, so that the contact voltage between iron and carbon increases, resulting in an increase in power consumption;
Aluminum electrolysis production process, with the use of the anode, the most of the sulfur will be released in the form of SOC2, causing pre-baked anode surface crack, the resistivity increases further, impellers, slag and anode brittleness increases, at the same time the product is in use in excess residue, which resulted in increased pre-baked anode consumption, resulting in pole changing cycle ahead.
Sulfur in petroleum coke is a harmful element in terms of environment, equipment maintenance and carbon product quality, and the higher the sulfur content, the worse the quality of petroleum coke. However, due to the expansion of petrochemical industry scale in China, the output of high sulfur coke is more and more, and the problems are more and more. Therefore, through the blending process of petroleum coke, high sulfur coke and low sulfur coke will be mixed in a certain proportion, on the basis of ensuring product quality, low cost to reduce the sulfur content of petroleum coke, become the focus of enterprise attention.
In this paper, through long-term research and experiment, calcined petroleum coke with different sulfur content respectively, and tested and analyzed the calcined coke, and reached the following conclusions:
The low sulfur content of petroleum coke reacts slowly to calcination temperature, and the sulfur content of petroleum coke does not decrease obviously with the increase of calcination temperature.
The sulfur content of petroleum coke with high sulfur content decreases rapidly when calcination temperature reaches a certain temperature. For high sulfur petroleum coke, when the temperature rises to a certain boundary point, the desulfurization is suddenly intense, and the higher the critical temperature is, the more intense the desulfurization is.
The volume density of high sulfur petroleum coke reacts quickly to calcination temperature. When the calcination temperature rises to 1350℃, the sulfur bond is destroyed, and the sulfur is separated from the carbon and sulfur bond. A large number of small pores are formed in the petroleum coke, resulting in a sharp decrease in the volume density of calcined petroleum coke.
When the calcination temperature rises to 1400℃, the air reactivity of high sulfur coke is improved, and the air reactivity index of high sulfur petroleum coke is worse than that of low sulfur petroleum coke at the same calcination temperature.
Sulfur can prevent the movement of sodium in the calcination process. If the desulfurization of high-sulfur petroleum coke is well controlled in the calcination process, the pre-baked anode of high-sulfur petroleum coke production can also have good air reactivity.
The volume density of raw anode and the amount of coal pitch used in the forming process are largely determined by the bulk density of calcined coke, and the air reactivity of the finished product of pre-calcined anode, the consumption of air reactivity in the electrolytic cell and the generation of carbon slag are directly related to the air reactivity of calcined coke.
Therefore, different calcination process parameters should be used in calcination production for petroleum coke with different sulfur content, especially when high sulfur petroleum coke is used as Raw material for pre-baking anode, the calcination cycle of petroleum coke should be extended as far as possible, and the calcination zone temperature should not be too high, preferably not higher than 1300℃.
But from the production practice, from the practical performance of the anode, in the case of constant sodium and calcium content, high sulfur content can reduce the coke activity in the CO2 atmosphere, reduce the mass loss. When the sulfur content of anode is higher, the CO2 reactivity index is better, and sulfur has a certain inhibitory effect on the CO2 reaction of anode. Therefore, sulfur content should not be too low when petroleum coke is mixed.
In conclusion, the sulfur content of petroleum coke used for pre-baked anode production should not be too high or too low, and the mixed petroleum coke with sulfur content in a certain range by blending process has a good effect on product quality.