A new fine-coal cleaning circuit, with potential near-term applications, has been evaluated for treating fine coal (i.e., 28 mesh x 0). This circuit combines a surface-based separator known as Microcel™ column flotation with an enhanced gravity separator known as the Multi-Gravity Separator (MGS). The synergistic effect of combining both processes in a single circuit resulted in improved ash and pyritic sulfur rejection with minimal losses in energy recovery. In addition, technical and economic analyses of this processing scheme suggest it compares favorably with existing post-combustion desulfurization techniques.

A detailed study of the MGS included the development of a model based on fundamental principles of fluid mechanics and mineral processing. The theoretical analyses identified drum speed as the most important MGS operating parameter. To validate these findings, a detailed parametric test program was conducted using coal samples from the Pittsburgh No. 8 and Illinois No. 6 seams. A statistical analysis of the test data also showed that drum speed was the most important variable in controlling the performance of the MGS. The other controlling parameters, i.e., feed percent solids, feed rate and wash-water addition rate, were found to be of lesser importance. The experimental test results were found to be in good agreement with the theoretical predictions obtained using the model.