In Bubbling Fluidized Bed Combustors (BFBC) utilizing coal, efficient combustion requires that feed size of coal particles be in the maximum size range of 2 to 6 mm. This requires that the comminution process be effective. In this work, various types of coals have been comminuted in an impact crusher. The size reduction process is characterized by four process parameters and relevant properties of the coal samples. Taguchi's design of experiment was used to minimize the number of experiments done to obtain meaningful results. It was concluded from the experiments that among process parameters, RPM has a more prominent effect on generation of fines compared to feed rate, feed size and gap setting. Among coal properties, volatile matter, ash content and fixed carbon have significant effect, followed by moisture content. RPM has relatively less influence on coarse particle (> 6 mm) content. An empirical correlation has been formulated based on the data to predict the generation of fines for a given set of process parameters and physical properties of coals. The results obtained using the model was within the acceptable accuracy when compared to the experimental data. The same correlation has also been applied successfully to fit the cement production from a plant, indicating that it has merit beyond the laboratory and that the specific type of crusher is immaterial, provided the mechanism of size reduction remains the same. (C) 2008 Elsevier B.V. All rights reserved.