Upgrading and advanced cleaning technologies for low-rank coals

Abstract Low-rank coals–lignite and subbituminous coals–refer to the lowest and second lowest rank of coals. Unlike high-rank coals deposited in specific areas, low-rank coals are evenly distributed around the world and their reserves are approximately 500 billion tons, which is similar with that of high-rank coals. Low-rank coals are high in moisture or ash content and susceptible to spontaneous combustion. Since low-rank coals are high in moisture, using them as fuel in energy-producing facilities like power plants increases coal consumption, emitting more CO 2 and lowering power generation efficiency. This chapter introduces upgrading and advanced cleaning technologies, which are low-carbon utilization technologies. Upgrading is necessary to use as a fuel for high efficiency and low emission combustion and conversion technologies. Upgrading is a process of removing moisture or ash from low-rank coals before using the coals to enhance facility efficiency. As such, we would like to introduce existing coal drying technologies and stabilization technologies as well as new drying/stabilization technologies, which are under development. This chapter also introduces the production technology of ash-free coals which is expected to be used for various purposes in the future.