METHOD FOR TREATING EXHAUST GAS

PURPOSE:To enhance the capacity of an electric precipitator without causing the lowering in the activity of a denitrating catalyst and the rising in pressure loss, by spraying a conditioning agent-containing liquid to coal firing exhaust gas subjected to dry denitration to form a dry solid which is, in turn, collected by the dry electric precipitator. CONSTITUTION:The gypsum slurry flowing out from a wet dehydration apparatus 17 is supplied to a dehydrator 22 from a line 21 to draw out a part of a filtrate to a line 27 and receives the addition of a conditioning agent such as Na2CO3, NaOH or Na2SO4 from a conditioning agent supply line 3 to be sprayed in the dust-containing high temp. exhaust gas between a dry denitration apparatus 6 and a dry electric precipitator 12 through a sprayer 33. Waste water containing the conditioning agent is dried and solidified by the heat of exhaust gas while the formed solid is discharged out of the system along with dust from the dry electric precipitator 12 through a collection line 13. The addition amount of the conditioning agent is set so that Na, in dust is 0.5-3wt% as Na2O. Further, the slurry is pref. sprayed so as to form fine particles with a particle size of 100mum or less.