The invention relates to a method for removing
nitrogen oxides in
waste gas or
flue gas, comprising the following steps of: connecting an absorbing
tower in series on a
waste gas or
flue gas conveyingpipeline at the front of an
exhaust pipe, adding NO2 at the front of the absorbing
tower and introducing the NO2 into
flue gas or
waste gas flow for mixing after being metered, then using a removingagent to treat the
mixed gas by absorbing and removing of the absorbing
tower with the removing agent and then discharging the
mixed gas from the
exhaust pipe; and adopting the following technical scheme: connecting the absorbing tower in series on the waste gas or
flue gas conveying pipeline, connecting a
nitrogen dioxide cylinder laterally at the front of the tower to directly add NO2 into the waste gas or
flue gas conveying pipeline or connect a
catalytic converter and an oxidizer laterally at the front of the absorbing tower, oxidizing NH3 released by a
liquid ammonia cylinder into NO2 which is then mixed in the
flue gas or waste gas conveying pipeline, and then carrying out absorbing and removing treatments by the absorbing tower. The method overcomes the defects that the existing method for denitrifying and denitrating waste gas or flue gas has complex treating technique, high cost, large waste and higher condition and requirements on treated flue gas and waste gas and the like,is applicable to denitration of flue gas and waste gas of
nitrogen oxides containing
nitric oxide as main material, and is especially applicable to removing
nitrogen oxides of flue gas of a boiler.