The particle size of slack coal is 0 ~25 mm. The slack coal is often used as combustion agent in steel company, thermal power plant, etc. The consumption of coal is quite large in thermal power plants. Take a 1 million kW thermal power plant for example, coal consumption amounts to 11,000- 13000t a day, which takes 60% ~ 80% of the cost for generating electricity. It is advisable to adopt appropriate coal mill for coal grinding. This can not only improve the utilization of coal, but also contribute to energy saving, environmental protection, economic benefits.