PURPOSE: To increase denitration efficiency by injecting NH3 and aq. H2O2 soln. of low concn. into NOx-contg. gas.

CONSTITUTION: Into NOx-contg. gas is injected spray of NH3 and aq. H2O2 soln. of concn. not higher than 30wt%, pref. not higher than 10wt%, or more pref. not higher than 3wt%. The lower the concn. of the aq. H2O2 soln. is, the less is the formation of NO2 because no local, high H2O2 concn. zone is formed. The formation of NO2 inhibits the denitration due to the reaction of NO with NH3. Addn. of H2O2 causes the noncatalytic denitration to processed even at a low temp. region, with increase in denitration efficiency for combustion gas.