Breakage and Mass Transport of Coal Particles in Ring-roller Mills

A mathematical model was developed for a ring-roller mill based on specific rates of breadage, primary breakage distributions and primary and secondary classification parameters. The model parameters were evaluated by laboratory and pilot-scale tests. At first, the specific rates of breakage and breakage distribution parameters of various types of coals were measured in a batch roller mill. Secondly, the primary classification of particles falling back onto the grinding table due to gravity and the secondary classification due to the built-on classifier were studied in model classifiers and empirical operating-design equations were then developed. Lastly, steady-state continuous grinding tests were carried out in pilot-scale mills to correlate variations of scale factors with make-up feed rates, mill geometry and operating conditions. Furthermore, empirical correlations on mass transport through the mills were also developed. The validity of the model was verified by steady-state data obtained in pilot- and industrial-scale mills. The effect of various operating conditions on the mill performance was first investigated by model simulations. The unsteady-state behaviors of a mill were then predicted by the model.