CHARACTERIZATION OF COAL-WATER SLURRIES PRODUCED IN A HIGH-SPEED STIRRED-BALL MILL

A comparison of energy requirements and rheological properties has been carried out for grinding of coal/water slurries produced in high-speed stirred and conventional ball mills. In each case, a linear population balance model using specific energy input as a reduced time variable resulted in a satisfactory description of the size distributions. The effect of stirrer speeds and fractional media filling on the energy efficiency has been studied. The pin device stirred mill was found to outperform the disc device stirred mill for this application.;Coal/Water slurries were found to behave as pseudoplastic fluids and data fitted to a power law type of relationship. Slurries produced to a fineness of 80% passing 250 mesh in conventional and stirred mills showed that the slurry prepared in a stirred mill was more viscous at low shear rates (;An approach of response surface methodology has been used to evaluate the optimal conditions of grinding. The operating variables examined were percent solids, ball size, dispersant dosage and mill speed. The results of grinding experiments based on central composite design have been evaluated in-terms of slurry rheology and desired distribution modulus. Comparison of conventional and stirred milling tests showed that the energy reduction which is possible with the stirred ball mill increases linearly with the percent of material passing 325 mesh up to 90% and beyond this point energy reduction is even higher.