The role of thinners in coking

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When coal materials with medium or high fluidity and high volatile matter are used in coking along with carbon-containing inert additives such as anthracite powder, semi-coke powder, or coke powder (thinning agents), the rate of shrinkage during the coking process can be reduced and cracks can be minimized. This not only improves the strength and size of the coke but also allows for the use of a wider range of coal sources for coking, as well as the recycling of coke powder. (1) For coals with high fluidity, retarding agents can adsorb a certain amount of liquid phase substances, reducing the fluidity and swelling degree of the colloids. This facilitates the separation of gaseous products and lowers the porosity. Meanwhile, the increased viscosity of the colloids leads to thicker pore walls, thereby improving the porous structure of the coke and enhancing its microstructural strength. However, the fluidity and swelling degree of colloids can only be reduced to a certain extent; otherwise, the adhesiveness will decrease, affecting the wear resistance of coke. (2) For coals with high volatiles, retarding agents can reduce the volatiles in the coal blend, decrease the shrinkage of semi-coke, thereby reducing coke cracks and improving its crush resistance. However, if the volatiles of the retarding agent are too low and its own shrinkage is too small, this increases the difference in shrinkage between it and the coal, leading to localized cracking in the coke. (3) Thinning agents such as semi-coke powder, coke powder, and iron shavings have good thermal conductivity, thereby reducing the temperature gradient between adjacent layers and minimizing thermal stress.