Improvement in coke strength against abrasion is needed for a stable operation of blast furnace. Pore structure of coke (e.g. pore size distribution and tortuosity) is important for an improvement of coke abrasion strength, because its effect influences CO₂ diffusion coefficient and coke strength after CO₂ reaction. In this study, production of coke samples having different pore structure was attempted by blending different size of slightly caking coal to coal blend. The effect of pore structure on CO₂ reactivity and abrasion after CO₂ reaction was investigated.
In case that larger size (2-3 mm) slightly caking coal was added to coal blend and carbonized (Coke A), the pore size distribution of coke became wider and contained larger pore which had higher value of tortuosity than the coke produced by adding smaller size (1-2 mm) slightly caking coal particles (Coke B). Difference in pore structure is considered to be originated by bubble size generated during softening of coal particles. Relationship between pore size and tortuosity is caused by the quantity of bottle-neck type pores in coke.
The reactivity of Coke A was higher and the extent of the reaction at inner part of coke lump analyzed by X-ray computerized tomography was larger, compared with the Coke B. These differences are considered to be based on the fact that large pore enhances diffusion of CO₂ into inner part of the coke, and that concentration of shear stress easily occurs around large pores.