Exhaust duct for a fossil fuel powered engine comprising a dilution selective catalytic reduction system

A power plant comprising:

• a gas turbine, and
• an exhaust duct for an engine, the exhaust duct comprising
• an exhaust gas passage carrying exhaust gas,
• a cooling fluid passage carrying a cooling fluid,
• a mixing device for mixing the cooling fluid with the exhaust gas,
• at least a selective catalytic reduction catalyst arranged in the exhaust gas passage for removing nitrogen oxides, and
• at least one injection nozzle to supply a reducing agent,
• wherein the mixing device comprises a mixing chamber with a first wall and an opposed second wall, the first and second wall arranged upstream of the selective catalytic reduction catalyst in the exhaust gas passage and extending over an entire cross-sectional area of the exhaust gas passage, both walls perforated by through holes, wherein the through holes of the first wall are connected with the through holes of the second wall in pairs by pipes extending through the mixing chamber, the pipes are each perforated by at least one hole into the mixing chamber and the cooling fluid passage ending into the mixing chamber.