An air quality control system for treating flue gas produced in a combustion process to produce cleaned flue gas comprising a combustion boiler equipped with an air preheater arranged for flue gas flow from the boiler through a duct and into the air preheater, a dry flue gas desulfurization reactor having a distribution device, ductwork for flue gas of a reduced temperature flow from the air preheater to the dry flue gas desulfurization reactor, a sorbent supply operable to supply a sorbent to the distribution device of the dry flue gas desulfurization reactor, a water supply operable to supply water to the distribution device, wherein the distribution device is operable for mixing water with the sorbent therein to produce a moistened sorbent for distribution in the dry flue gas desulfurization reactor, a particulate removal device operable to remove dried sorbent from flue gas following contact of the flue gas in the dry flue gas desulfurization reactor to produce cleaned flue gas, characterized by a duct (38a, 58) for transport of dried sorbent from the particulate removal device into the duct arranged between the boiler and the air preheater for reaction with flue gas SO 3 and acid gases and for transport of moistened sorbent from the distribution device for injection of the sorbent into the duct arranged between the boiler and the air preheater for reaction with flue gas SO 3 and acid gases, wherein the water supply is fluidly connected to the duct (38a, 58) via fluidly connected pipe for transporting water to the duct (38a, 58) for mixture with dried sorbent and/or moistened sorbent for injection into the duct arranged between the boiler and the air preheater. a combustion boiler equipped with an air preheater arranged for flue gas flow from the boiler through a duct and into the air preheater, a dry flue gas desulfurization reactor having a distribution device, ductwork for flue gas of a reduced temperature flow from the air preheater to the dry flue gas desulfurization reactor, a sorbent supply operable to supply a sorbent to the distribution device of the dry flue gas desulfurization reactor, a water supply operable to supply water to the distribution device, wherein the distribution device is operable for mixing water with the sorbent therein to produce a moistened sorbent for distribution in the dry flue gas desulfurization reactor, a particulate removal device operable to remove dried sorbent from flue gas following contact of the flue gas in the dry flue gas desulfurization reactor to produce cleaned flue gas, characterized by a duct (38a, 58) for transport of dried sorbent from the particulate removal device into the duct arranged between the boiler and the air preheater for reaction with flue gas SO 3 and acid gases and for transport of moistened sorbent from the distribution device for injection of the sorbent into the duct arranged between the boiler and the air preheater for reaction with flue gas SO 3 and acid gases, wherein the water supply is fluidly connected to the duct (38a, 58) via fluidly connected pipe for transporting water to the duct (38a, 58) for mixture with dried sorbent and/or moistened sorbent for injection into the duct arranged between the boiler and the air preheater.