The rapid development of the world electrolytic aluminum industry has pushed the demand for carbon anodes and petroleum coke, while petroleum coke is only a byproduct of refineries. Refineries do not attach much importance to the improvement of petroleum coke quality and strict quality grading management, and their coking process and control of raw materials for coking are usually not guided by the quality of petroleum coke. Sometimes, due to the inferior quality of raw materials for coking, the shortening of coking time or improper operation of decoking process in the coke tower, a large number of coke breeze and shot coke will be produced.
In recent years, the content of coke breeze in petroleum coke has an increasing trend, especially the content of fine coke breeze below 1 mm directly affects the calcination of petroleum coke and the production of carbon anode.
Decrease of the calcination yield: Coke with high content of coke breeze is burned seriously in the calcination process, and coke breeze is easily sucked out by negative pressure, especially in the rotary kiln. Although the influence of the retort calciner is relatively small, the existence of coke breeze tends to cause coking on the furnace wall and blockage of the flame path.
Under the same conditions, the calcination degree of coke breeze is not as good as that of granular coke. Tests show that calcined coke with a large amount of coke breeze ( 25 %-40 % ) is significantly different from calcined coke with a coke breeze amount of ( 10 %-15 % ) in terms of true density, tap density, porosity, strength, resistivity and oxidation of coke particles.At the same time, due to the poor thermal conductivity of the coke breeze, excessive amount of the coke breeze will cause uneven calcination and affect the quality of the calcined coke and the strength of the calcined coke.
The increase in the amount of coke breeze increases the difficulty of reasonable control of the following anode formula, which leads to the contradiction between material balance and process formula in the production process. Usually, anode factories have to adjust the formula to suit the situation of material thinning in order to ensure the continuity of production, thus bringing adverse effects on the quality stability of carbon anodes.
In addition, the increase of coke breeze will increase the amount of dust, thus increasing the burden of dust collection equipment. Once it exceeds the capacity of dust collection equipment, it will lead to environmental problems on the whole site.
Compared with needle coke and sponge coke, the shot coke has distinct characteristics. Petroleum coke can be divided into sponge coke, needle coke and shot coke according to its microstructure. The shot coke is similar to pebble coke and has a smooth and loose spherical coke mass with a diameter as small as sand particles and as big as basketball. The shot coke produced by different devices with different raw materials has slightly different shapes, but its interior is composed of small spheres of about 5 mm. This coke is not suitable for producing carbon anode products:
The shot coke wraps some smaller shot coke inside after crushing, and although its compacted packing density after calcination can meet the requirements of prebaked carbon anode, due to the smooth appearance, inconsistent internal structure and external appearance of shot coke and lack of pores on the surface, the good adhesion between shot coke and binder coal tar pitch is hindered, making it difficult for the binder to penetrate into the interior of the coke, resulting in poor adhesion and easy occurrence of internal defects
The higher thermal expansion coefficient of shot coke is also one of the factors causing thermal shock cracking during anode baking.
The shot coke is relatively hard, dense and non-porous, and its HGI value can be as low as 27, while the HGI value of the common anode petroleum coke is between 70 and 90, and it is difficult to break the shot coke with high hardness, which will increase the wear and operation difficulty of the equipment.
The calcined petroleum coke provided by our company is Sponge Pet Coke.More details of that on our website：https://jhcarbon.com/product/calcined-pet-coke