Abstract
Three types of mill, such as a roll mill, a jaw crusher and a hammer mill, are used as coarse pulverizing devices to find suitable pulverizing conditions for mineral liberation of two kinds of high-ash coals. High-ash coal A, containing a large amount of quartz, and coal B, containing clay, were used as test samples. It was found that the roll mill was the most efficient device, and its characteristic of mineral liberation is suitable to implement an efficient mineral removal method. A grinding load above 1.0 kN in the roll mill for coal A had little effect on mineral liberation, however, the characteristic of mineral liberation and grindability were improved with increasing the roll rotational speed. On the contrary, the mineral liberation for coal B tends to improve at lower roll rotational speeds. Consequently, combustible recovery of 80% and mineral removal ratio of 60% were obtained in the mineral removal test of these coals. Furthermore, it is possible to reduce mineral matters in high-ash coal, such as low-grade coal, to 20 mass% by choosing suitable conditions for coarse grinding mills.
