Structure and Calcination Characteristics of Green Coke in Different Parts of the Delayed Coking Tower

Abstract

Due to the difference in feeding time and reaction temperature distribution, the performance of green coke in different parts of the delayed coking tower is also different. In this paper, the coal-based green coke in the upper, middle, and bottom parts of the delayed coking tower are selected to study their structure and calcination characteristics, which lays a foundation for the classification and quality utilization of green coke. The results show that the upper green coke has the lowest true density, the highest volatile content, the lowest condensation degree, the highest branch index, and the least fibrous texture structure. The bottom green coke has higher aromaticity, less branched chain, and more fibrous texture structure than that of the upper green coke. The middle green coke is more uniform and has the best texture structure. The 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 were calcined from 700°C to 1500 °C, the upper, middle, and bottom calcined cokes showed an increase in true density, a decrease in electrical resistivity, and a decrease in N content, and their fiber texture and carbon microcrystalline structure tended to be regular and orderly. However, when the calcination temperature is lower than 1000 °C, the difference in the parameters of the three parts of calcined coke is relatively obvious. Even if the calcination temperature is higher than 1000 °C, 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. In order to achieve a similar index value and microstructure, the calcination temperature of upper green coke should be 100~200 °C higher than that of middle and bottom green coke.

Keywords: Needle coke, delayed coking tower, green coke, calcination characteristics