Study on Relationships between Coal Microstructure and Coke Quality during Coking Process

Optimizing coal blending is important for high-quality development of coking industries, among which deep understanding of relationships between coal characteristics and coke quality is critical. This work selected four typical coals from Shanxi Province in China to investigate influences of their structures and properties on coke quality. Although these samples belong to coking coals, the mechanical strength and thermal strength of the corresponding cokes are quite different. Macerals in coals, especially vitrinite, have significant effect on thermal strength of cokes. The thermal strength of coke B is better than coke A, because coal A mainly contains desmocollinite and coal B has more telocollinite. The CSR of coke B, C and D is higher than 60%, indicating they possess good thermal property. In the coking process, relatively low initial softening temperature (<400 degrees C), wide plastic temperature range (>100 degrees C), smooth fluidity region and appropriate maximum fluidity is helpful to improve coke quality based on Gieseler fluidity analysis. Coal C and Coal D have lower condensation degree, shorter aliphatic chain, and more hydrogen bond, which reveals that the condensation degree and hydrogen bond play important roles on the formation of plastic mass and coke thermal strength. Coke A shows unsatisfied properties because coal A has higher condensation degree and less hydrogen bond. In addition, TG-MS and CH4 evolution characteristics also imply the volatile matter released from coal A during pyrolysis mainly comes from the covalent bond with higher bond energy, which indicates that the chemical bond of coal A is more stable than other coals.

Automated summary

Optimizing coal blending is crucial for the high-quality development of coking industries. This study focuses on understanding the relationship between coal characteristics and coke quality by investigating the influence of coal structures and properties on coke quality using four typical coals from Shanxi Province in China. The presence of macerals, especially vitrinite, greatly affects the thermal strength of coke. The thermal strength of coke B is superior to coke A due to the difference in the composition of desmocollinite and telocollinite. Coke B, C, and D exhibit good thermal properties with a CSR value higher than 60%. The plasticity and fluidity characteristics analyzed through Gieseler fluidity analysis reveal that a low initial softening temperature, wide plastic temperature range, smooth fluidity region, and appropriate maximum fluidity contribute to improved coke quality. The condensation degree and hydrogen bond play significant roles in the formation of plastic mass and coke thermal strength, with coal C and coal D showing more favorable properties compared to coal A. Thermal gravimetric-mass spectrometry and methane evolution analysis indicate that the volatile matter released during pyrolysis of coal A primarily comes from covalent bonds with higher bond energy, suggesting the stability of the chemical bonds in coal A.