An air quality control system (AQCS) (14) useful for treating flue gas, such as flue gas produced by a fossil fuel fired boiler (12), is described. In addition to flue gas treatment, the AQCS (14) provides for air preheater (24) flue gas outlet (32a) flue gas temperature reduction and air preheater (24) corrosion prevention while reducing capital costs, increasing reliability and increasing operating flexibility with regard to fuel selection.