Subbituminous and lignite coals
contain relatively large amounts of
moisture (15% to 40%) compared to
bituminous coal (less than 10%). A
significant amount of the heat
released during combustion of lowrank
coals is used to evaporate this
moisture, rather than generate
steam for the turbine. As a result,
boiler efficiency is typically lower for
plants burning low-rank coal. The
technologies include using waste
heat from the flue gas and/or cooling
water systems to dry low-rank coal
prior to combustion.