The invention relates to a method for simultaneously removing
sulfur oxides and
nitrogen oxides in
flue gas by using aqueous
ammonia. According to the method, the (NH4)2SO3, which is obtained from a desulfurization reaction for absorbing SO2 by aqueous
ammonia, is used as an absorption solution for a
denitrification reaction; and the (NH4)2SO3 has reducibility for reducing
NOx in the
flue gas to N2 to achieve the
denitrification purpose. The method provided by the invention comprises the following steps that: the
flue gas firstly enters into a
denitrification spraying layer of a contraction segment in a venturi
tower and is subjected to a downstream
contact reaction with a circulating liquid from an
oxidation pond on the
tower bottom, an aqueous
ammonia spraying layer is arranged at the
throat part of the venturi
tower to carry out the desulfurization reaction, the concentration of the (NH4)2SO3 is instantly increased due to the desulfurization reaction, the denitrification reaction is further carried out, the liquid after reaction and the
flue gas transversely enter into the middle lower part of a cylindrical tower along the lower part of the venturi tower, the liquid flows downwards to the bottom of the cylindrical tower, the
flue gas moves upwards after passing through a tower plate and is countercurrent contact with the circulating liquid to further generate a desulfurization reaction and a denitrification reaction, fine liquid drops and
aerosol of the purified
flue gas are captured when the purified flue gas passes through the water spraying layer and a folded plate type defroster, the purified flue gas is then directly exhausted from a direct exhaust
chimney connected to the tower top, and simultaneously, a by-product of the
system is
ammonium sulfate, which is a
raw material of an agricultural nitrogenous
fertilizer or a compound
fertilizer.