Effect of coal tar pitch on highly reactive coke properties and microstructure

Highly reactive and high-strength cokes are important for developing and producing hydrogen-rich blast furnaces. The work aimed to produce cokes with high reactivity and high post-reaction strength. The coal tar pitch (CP) was added to improve the post-reaction strength of cokes on the premise of adding alkali metals or alkaline earth metals to improve the reactivity of cokes. The chemical reactivity index of coke samples generally decreases by about 1%, while the post reaction strength of coke samples shows a significant improvement after the addition of coal tar pitch, with coke rich in CaO increasing by about 6% and coke rich in K2CO3 and Na2CO3 increasing by about 3% after adding the CP. Besides, the structural strength and micro strength of coke samples from the composite CP were improved. The microstructure analysis of the coke samples before and after the composite CP showed that the addition of the CP could weaken the originally developed pore structure of the coke samples and reduce the surface area of the gasification reaction of coke samples. Therefore, the gasification reaction of coke samples was inhibited. Moreover, the CP reduced the damage of alkali or alkaline earth metals to the dense aromatic-ring structure in the carbon matrix during the carbonization process of coking coal. It increased the amount of qualitative carbon in the coke samples and the order of carbon microcrystals. The effect of the CP on coke samples varied due to differences in coking coal and catalyst types.