GAS PHASE REDUCING METHOD OF NITROGEN OXIDE CONTAINED IN WASTE GAS

PROBLEM TO BE SOLVED: To reduce nitrogen oxide with high reactivity and high selectivity in the presence of no catalyst by adding a reducing agent previously partially oxidized under a specific condition into a waste gas and allowing the result to gaseous phase-react with the nitrogen oxide in the waste gas under a specific condition. SOLUTION: At least one kind of the reducing agent selected from among hydrocarbons and oxygen-containing organic compounds is added into a part taken out from the waste gas containing the nitrogen oxide and is partially oxidized under the condition of 5-50% oxygen concentration at 350-800 deg.C for the holding time of 0.05-1sec. Next, the reducing agent gas containing the partially oxidized reducing agent is added into the wast gas containing the nitrogen oxide so that the quantity of the reducing agent becomes equal to or more than 1.5 times of that of the nitrogen oxide expressed in terms of C1 at the reducing agent is allowed to gaseous phase-react with the nitrogen oxide in the waste gas under the condition of 5-50% oxygen concentration at 350-800 deg.C for the holding time of 0.05-1sec. As a result, the nitrogen oxide is decomposed into nitrogen and water to change the waste gas to a purified gas.