A discharge gas treatment apparatus and method which lower treatment cost
and which attain efficient removal of mercury contained in a discharge
gas are provided. The discharge gas treatment apparatus, includes a
cooling apparatus for controlling the temperature of the discharge gas to
a predetermined temperature in accordance with the hydrogen chloride
concentration of the discharge gas; an NO.sub.x removal catalyst unit for
reducing nitrogen oxide contained in the discharge gas and for causing
reaction between mercury and hydrogen chloride contained in the discharge
gas, the discharge gas having been controlled to the predetermined
temperature and having been introduced to the apparatus, with ammonia
being added thereto; and a wet-format desulfurization apparatus, disposed
on the downstream side with respect to the NO.sub.x removal catalyst
unit, for removing sulfur oxide and mercury chloride contained in the
discharge gas through dissolving sulfur oxide and mercury chloride in a
liquid absorbent.