Structure and calcination characteristics of green coke in different parts of the delayed coking tower

Due to the different coking environments, the properties of green coke in different parts of the delayed coking tower is also different. In this paper, coal-based green coke in the upper, middle, and bottom parts of the delayed coking tower were selected to study their structure and calcination characteristics, thus laying a foundation for green coke’s classification and quality utilization. The results show that the upper green coke has the lowest true density, highest volatile content, lowest condensation degree, highest branch index, and least fibrous texture. The bottom green coke has higher aromaticity, less branched chain, and more fibrous texture than the upper green coke. The middle green coke is more uniform and has the best texture structure. Carbon microcrystalline structure parameters of the middle and bottom green coke are similar, while the interlayer space (d002) of the upper green coke is the largest, and its ideal graphitic carbon content is the lowest. When the green cokes are calcined from 700℃ to 1500 ℃, the upper, middle, and bottom calcined cokes all show an increase in true density, a decrease in electrical resistivity, and a decrease in N content, and their fiber texture and carbon microcrystalline structure tend to be regular and orderly. However, when the calcination temperature is lower than 1000 ℃, the difference in the parameters of the three parts of calcined coke is relatively apparent. When the calcination temperature is between 1000 ℃ and 1500 ℃, the parameters of the upper calcined coke are still significantly different from those of the middle and lower calcined cokes, while the results of the middle and bottom calcined cokes on the microscopic surface and carbon microcrystalline structure, N content and electrical resistivity are similar. To achieve a similar index value and microstructure, the calcination temperature of upper green coke should be 100~200 ℃ higher than that of middle and bottom green coke.