A heat recovery steam generator includes a casing for receiving exhaust gas from a turbine, a heat exchanger positioned within the casing for thermal communication with the exhaust gas, and an ammonia vapor distributor positioned within the casing. An ammonia vaporization unit is configured for conversion of aqueous ammonia to ammonia vapor and communication of the ammonia vapor to the distributor. A first extraction line operatively connects between the casing and the ammonia vaporization unit for communication of exhaust gas to the ammonia vaporization unit. A second extraction operatively connects between the casing and the ammonia vaporization unit for communication of exhaust gas to the ammonia vaporization unit. A catalytic reduction system is located within the casing and positioned downstream from the distributor for effecting a reaction between the ammonia vapor and NOx in the exhaust gas.