An air quality control system (AQCS) 14 useful for treating flue gas FG, such as flue gas FG produced by a fossil fuel fired boiler 12 is described. The AQCS 14 is equipped with a dust separator 37. The dust separator 37 is useful under relatively high dust load conditions downstream from a dry scrubber reactor 36 with limited equipment wear and limited space requirements. As such, the dust separator captures particulate matter with a dust trap that intercepts the flow of particulate matter for collection of the particulate matter in a hopper.