Abstract: In a coal-fired boiler, a heat recovery unit is located upstream of a dry electrostatic precipitator so as to reduce the temperature of exhaust gas flowing to the dry electrostatic precipitator and thus prevent reverse ionization in the electrostatic precipitator. The heat recovery unit located upstream of the dry electrostatic precipitator will in no way be corroded even if the concentration of dust is reduced in the dry electrostatic precipitator. A desulfurization unit does not require a cooling/dust removing section and eliminates the need for a wet electrostatic precipitator. The dry electrostatic precipitator includes a gas passage divided into a plurality of parallel passages and dampers operable to close the passages. This arrangement prevents dust from being dispersed as a result of hammering without charge.