PURPOSE: To prevent a dispersion of dust by a method wherein an air heated at a low temperature is applied as a hot temperature fluid at a gas reheater unit, an adhesion of dust or corrosion caused by sulfuric acid at the gas reheater is decreased, an electrostatic precipitator is mounted at a relative low temperature area, while a minituariazation and an effect of collection are promoted and a dry type dust collector is mounted at the downstream of the gas reheater unit.

CONSTITUTION: NOx is removed by a denitrification device 2, heat-exchanged with combustion air with its temperature decreased at a gas reheater 5, heat- exchanged with combustion air at a low temperature air preheater 9, its temperature is decreased, then the dust is removed by an electrostatic precipitator 10, thereafter SOx is removed by a desulfurization device 6, the gas is reheated with a gas reheater 5 and then discharged into the surrounding atmosphere. In view of the dispersion of dust in the processed discharged gas, the dry type dust collector 11 is mounted downstream of the gas reheater 5. In this way, two units of air preheaters are arranged to facilitate a removal of dust, an adhesion of dust and a corrosion caused by sulfuric acid at the gas reheater can be reduced and also the dispersion of dust into the surrounding atmosphere can be prevented.