Micronization of Hard Coal with the Use of a High-Pressure Water Jet

This paper presents an original method for the micronization of coal particles in a hydro-jet mill, which allows effective comminuting of coal in the pressure range of 100–250 MPa, at a variable water flow rate of 0.2–0.5 dm3/s. The discussed high-pressure water jet mill (HPWJM) allows the comminution of standard fines, with a grain size up to 2 mm, and at a relatively high comminuting efficiency of 8 to 55 g/s. In addition, the paper presents energy-consumption ratios, and indicates the advantage of this method over mechanical grinding in a planetary ball-mill. At optimum conditions, coal comminution at an efficiency of Qc = 38.4 g/s and at an energy input of EH = 1.1 MJ/kg provides an average particle size of about 40 µm. The degree of comminution was further improved by applying roto-turbulent micronization, which resulted in an average size of comminuted coal particles of only 17 µm. As an additional result, the actual surface area of the particles increased by 10–30 thousand times when compared to ground fines—this fact is of significance for the application of micronized particles in quasi-liquid coal-water fuel.