Pressurized flash drying charateristics using sub-bituminous coals for circulating fluidized bed gasifier

Low rank coals are abundant, easily accessible and mineable with low costs. However thermal efficiency of low rank coal is relatively low and it can increase fire risks and transportation costs because of high moisture content. Therefore drying or dewatering prior to thermo-chemical conversion processes, such as combustion, gasification and so on, should be inevitably used for the economical usage of low rank coal. Especially gasification offers one of the most versatile and clean ways to convert fossil fuel or biomass resources into electricity, hydrogen, and other valuable products. Among various gasifiers, circulating fluidized bed (CFB) gasifiers might be the most suitable option to gasify low rank coal and biomass resources because of advantages of CFB gasifiers. Even if CFB gasifier is used, moisture in low rank coals should be reduced to improve gasification efficiency. To study flash drying characteristics a pressurized flash drying system was designed and experimented. The effects of pressure (up to 40 bar), drying temperature (up to 600 oC), particle size (212-300 μm, 300-355 μm) on drying ratios were investigated. As a result, the drying ratio increases with temperature and length of drier. However, an increase of pressure was not always good solution.