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Characteristics of Graphitized petroleum coke
来源: | 作者:jzc-cokes.com | Publish time:2021-07-14 | 18 Views: | 分享到:

Physical properties of graphitized petroleum coke include ash, sulfur, volatile, true density, porosity, resistivity, coefficient of thermal expansion and mechanical properties.

Ash content of graphitized petroleum coke

The main elements in the ash of graphitized petroleum coke are iron, silicon, calcium, aluminum, sodium, magnesium, and a small amount of vanadium, titanium, chromium, etc. The content of vanadium in graphitized petroleum coke should be limited in the production of anode materials for electrolytic aluminum and graphite anode for electrolytic sodium chloride solution. The first factor affecting the ash content of graphitized petroleum coke is the salt content and desalting degree of crude oil. Most of the salt in crude oil is enriched in residual oil after distillation or cracking, and a small part is deposited in furnace tubes, containers and equipment, while most of the salt in residual oil is left in coke. The ash content of Graphitized petroleum coke is also affected by the salt content of cooling water and high-pressure water for coke unloading, especially the repeatedly reused cooling water and high-pressure water for coke unloading. If the produced graphitized petroleum coke is piled up in the open air, the sand on the ground or the sand brought by the wind will also increase the ash content of the graphitized petroleum coke. The ash content of the graphitized petroleum coke for the production of graphite products should generally be less than 0.5%, and the ash content of the graphitized petroleum coke for the production of high purity graphite should not be more than 0.15%.

Sulfur

Sulfur is one of the impurities that affect the quality of Graphitized petroleum coke. The sulfur content of Graphitized petroleum coke depends on the sulfur content of the residual oil. 30% - 40% of the sulfur in the residual oil remains in the graphitized petroleum coke. If the residual oil with higher sulfur content is hydrodesulfurized in advance to reduce the sulfur content in the residual oil, the sulfur content of the resulting graphitized Petroleum Coke will be reduced accordingly. The sulfur in Graphitized petroleum coke can be divided into two types: sulfur organic compounds (sulfide, mercaptan, sulfonic acid, etc.) and sulfur inorganic compounds (iron sulfide, sulfate). Generally, the desulfurization effect is not obvious when the calcination temperature is about 1300 ℃. Only when the calcination temperature is about 1450 ℃, can the desulfurization effect be obvious. Part of sulfide can be discharged only under the high temperature of graphitization. Sulfur is a harmful element for the production of anode materials for aluminum electrolysis and graphite products. The graphite electrode produced by Graphitized petroleum coke with high sulfur content produces "gas expansion" phenomenon in the process of graphitization, which easily leads to product cracks. When the graphite electrode with high sulfur content is used for steelmaking, the consumption per ton of steel electrode increases. The sulfur content of graphitized petroleum coke from most places in China is low, and only the sulfur content of graphitized petroleum coke produced by refineries using domestic or imported high sulfur crude oil is high.

Volatile matter

The size of volatile matter of graphitized petroleum coke indicates the coking temperature. The coking temperature of kettle coke is higher, up to 700 ℃, so the volatile matter of kettle coke is lower (3% ~ 7%), while the coking temperature of delayed coking Graphitized petroleum coke is only about 500 ℃, so the volatile matter is as high as 8% ~ 15%, The volatile matter of graphitized petroleum coke produced by delayed coking is not only determined by coking temperature, but also related to the loading time of residual oil into coking tower and the condition of steam blowing into coke bed. The volatile matter of coke discharged from the same tower also varies greatly. For example, the structure of coke at the bottom of tower is denser, the bulk density is higher, the volatile matter is lower, and the structure of coke at the top of tower is loose, The volatile is much higher. The amount of volatile matter of graphitized petroleum coke has little influence on the quality of carbon products, but it has influence on the calcination operation. It is difficult to calcine high volatile graphitized petroleum coke in general rotary kiln or pot furnace. It is necessary to reform the calcination equipment to meet the needs of calcining high volatile graphitized petroleum coke.

density

The true density of graphitized petroleum coke calcined at 1300 ℃ is the main item to measure the quality of graphitized petroleum coke. Generally speaking, the higher the true density after calcination, the easier the graphitization of this kind of coke, and the lower the resistivity and thermal expansion coefficient after graphitization. The bulk density of graphitized petroleum coke indicates the compactness of coke structure, and is proportional to the mechanical strength. In addition to the bulk density of coke, the tap density is also related to the particle size of coke.

resistivity

The resistivity of raw coke without calcination is very high, which is close to that of insulator. After calcination, the resistivity decreases sharply. The resistivity of Graphitized petroleum coke is inversely proportional to the calcination temperature. The resistivity of graphitized petroleum coke calcined at 1300 ℃ decreases to 500 μ About Ω· M.

Coefficient of thermal expansion

The thermal expansion coefficient of Graphitized petroleum coke mainly depends on the properties of residual oil, that is, the content of aromatics and asphaltenes in residual oil. The thermal expansion coefficient of graphitized petroleum coke produced from residual oil with high content of aromatics and low content of asphaltenes and resins is low. Needle coke is the same kind of Graphitized petroleum coke, and the thermal expansion coefficient is also different (see Table 1), Needle coke with low coefficient of thermal expansion should be used in the production of large-scale ultra-high power graphite electrode and joint blank. The coefficient of thermal expansion of Graphitized petroleum coke is related to the test temperature. The standard temperature for measuring the coefficient of thermal expansion in China is 100 ~ 600 ℃. The results obtained at different test temperatures can not be directly compared.

Mechanical properties

The mechanical properties of Graphitized petroleum coke include "fragility", brittleness and wear rate. The "fragility" and brittleness of Graphitized petroleum coke have a certain practical significance in the electrode manufacturing process. The fragility can be evaluated by the size ratio of coke before and after crushing, and brittleness is the possibility of coke crushing in the process of transportation and transmission. The wear rate of the original coke is directly proportional to the volatile content and inversely proportional to the bulk density. The wear rate of the calcined graphitized petroleum coke decreases significantly.