Abstract
An in-depth study on the characteristics of coke in the hearths of blast furnaces is of great significance for explaining the mechanism of coke deterioration in blast furnaces. In the present work, the changes in macromorphology, degree of graphitization, and microstructure of the coke taken from different hearth locations of a 5,800 m3 superlarge blast furnace during its intermediate repair period were systematically studied. Significant differences were found between cokes obtained from the edge ("edge coke") and from the center ("center coke") of the hearth in terms of properties and degradation mechanisms. Edge coke was severely eroded by liquid metal, and only a small amount of slag was detected in the coke porosity, whereas center coke was basically free from erosion by liquid metal, and a large amount of slag was detected in the coke porosity. The degree of graphitization of edge coke was higher than that of center coke. The carburizing effect of liquid metal was the main cause of the degradation of edge coke and made it smaller or even disappear. Center coke was degraded due to the combination of two factors: slag inserted into micropores on the surface of center coke loosened the surface structure; and graphite-like flakes that appeared on the center coke surface lowered the strength and caused cracks in the surface.
Highlights
Coke serves as the structural support, fuel, reducing agent, and carburizer in blast furnaces [1, 2]
This result implies that the area between 5.5 m and 7.5 from the hearth edge is the deadman of the 5,800 m3 blast furnace
Because the hearth diameter is as large as 15 meters, which makes it impossible for the air blast from tuyeres to blow through the center of the deadman and results in poor air permeability and poor fluid permeability, the inflow of liquid metal and consumption of coke in the deadman are greatly reduced, leaving the macromorphology of the coke in the deadman basically unchanged with clear edges and angles being apparent
Summary
Coke serves as the structural support, fuel, reducing agent, and carburizer in blast furnaces [1, 2]. As iron-making technologies advance, blast furnaces tend to be larger with higher rates of pulverized coal injection (PCI), a trend that raises higher requirements for coke quality [3]. As a response, exploring the mechanism of coke deterioration in blast furnaces is important for developing iron-making technologies. In the blast furnace process, high temperature and high pressure with extremely hostile conditions make it impossible to monitor the reactions in the furnace involving coke. This circumstance has greatly limited researchers’ understanding of the deterioration mechanism of coke in blast furnaces. Huiqing Tang [4], Zhen Miao [5] and Yuting Zhou [6] established a mathematical
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