STUDY ON THE GRINDING EFFICIENCY OF NON-DESIGN KARAZHYRA COAL IN BALL DRUM AND HAMMER MILLS

This paper presents a comparative study on the grinding efficiency of non-design Karazhyra coal using two main types of milling equipment: ball mills and hammer mills. The research was conducted to assess the suitability of local fuel for combustion in boiler units not originally designed for this type of coal. Laboratory sieve analysis was performed to determine the particle size distribution of the pulverized fuel. For the first time, polydispersity coefficients for Karazhyra coal dust, processed in both types of mills, were obtained and analyzed. Sieve residue measurements showed that in the product of the hammer mill only 0.2% of particles remained on the 400 µm sieve, whereas in the product of the ball drum mill this value was 2.5%. This indicates an almost complete elimination of coarse fractions during grinding in the hammer mill. It was found that with both grinding methods about 88% of coal dust particles are smaller than 200 µm. At the same time, the residue on the 90 µm sieve was 32% for the ball drum mill and 53% for the hammer mill. Thus, the hammer mill product is characterized by an increased proportion of medium-sized particles (90-200 µm) in the absence of an excessive amount of ultrafine fractions. The absence of coarse and ultrafine fractions during grinding in the hammer mill contributes to the formation of a higher polydispersity index of coal dust, which was 1.51, whereas for the ball drum mill it was only 0.78. The findings suggest that both mills are suitable for fuel preparation, but the hammer mill ensures better combustion quality and thermal efficiency. Therefore, it is recommended as the more effective solution for the preparation of non-design coal in thermal. The conducted studies serve as a basis for further study of the characteristics and behavior of nondesign coal in various operating modes.