PURPOSE: To efficiently remove the acidic gas in exhaust gas, by arranging a second dust collector between an alkali neutralizing agent-containing powder injection apparatus and a neutralizing agent injection apparatus and discharging the powder separated by said dust collector out of the system.
CONSTITUTION: The acidic gas-containing exhaust gas G discharged from an incinerator 1 is introduced into a powder injection apparatus 1. At the same time, the unreacted neutralizing agent and reaction product (R) recovered from a post stage dust collector 7 are injected in the powder injection apparatus 1 to be subjected to pretreatment. Subsequently, the unreacted neutralizing agent and the reaction product are recovered along with the fly ash contained in the exhaust gas from the beginning and transferred to an ash pit III to be separated. The exhaust gas G passing through a dust collector 3 receives the fresh alkali neutralizing agent C blown in from a neutralizing agent injection apparatus 2 to be neutralized. thereafter, the unreacted neutralizing agent and the reaction product (R) are recovered by the post stage dust collector 7 to be again injected in the powder injection apparatus 1.