Evaluation of the Performance of Air Dense Medium Fluidized Bed (ADMFB) for Low-Ash Coal Beneficiation. Part 1: Effect of Operating Conditions

Low-rank coals are widely used as fuel in coal-fired power plants. However, feeding such a coal in addition to lower efficiency generates a variety of problems mostly associated with the ash-forming minerals. An efficient dry coal cleaning method can offer a solution while avoiding problems associated with wet methods and generates partially dried coal. Air dense medium fluidized bed (ADMFB) can be an efficient and economical dry ash removal technology, but the comprehensive understanding on its performance is not yet openly available. In the present work, a detail study of the factors affecting the beneficiation of a low-ash lignite coal using ADMFB is provided. Response surface methodology supported by a central composite experiment design method is employed to study the effect of superficial air velocity (V), residence time (T), and bed height (H) on the performance of a batch ADMFB separator at three levels. Also, the effects of sample weights and particle size of lignite coal are separately studied. The system was found to effectively decrease the ash content of the clean coal product. The organic material recovery to clean coal product was affected negatively by H, V, and T, while T, H, and V were found to affect the separation efficiency positively. Various levels of interactions between parameters were also revealed and discussed. The optimum operating condition for maximizing the recovery was found to be 15 cm/s, 90 s, and 15 cm for V, T, and H, respectively. This condition led to a clean coal ash content, recovery, and separation efficiency of 10.6, 95.63, and 15.29%, respectively. The beneficiation test results also revealed that higher ash removal (23%) and recoveries (86%) are obtainable for coarser coal particles. Higher recovery and separation efficiency are achievable for larger sample weights (84.6 and 30.7%, respectively).