Energy-efficient fluidized bed drying of low-rank coal

An energy-saving and economical process was developed for drying low-rank coal using steam as the drying medium. Based on simulation tests, the energy consumption of the process was found to be nearly 30% lower than that of vapor recompression drying. The proposed process involves the removal of the freezable water in the coal in an exergy recuperative module, while the non-freezable water is removed in a heat integration module. During the removal of the freezable water, the evaporated water is compressed to a low pressure and recycled to the fluidized bed dryer for heat exchange with the incoming coal to minimize exergy destruction. Conversely, medium-pressure steam extracted from a steam turbine is used as the heat source for the removal of the non-freezable water. No compressor was used in the process which significantly reduced the capital cost. Moreover, technical feasibility has been verified through investigating the fluidization performance of the low-rank coal particles in the fluidized bed dryer during the proposed process, particularly to determine the effect of the increased heat exchange tubes on the fluidization performance.