Catalytic oxidation of SO2 to SO3 in the presence of fly ash

Claim 1

A combustion gas conditioning method whereby particulates are removed from the main stream of combustion gases containing sulfur dioxide in a flue by electrostatic precipitation means, said method comprising the steps of withdrawing from a location upstream of said electrostatic precipitation means a minor amount of the total volume of said combustion gases entering said flue, including the particulates associated with said minor amount of combustion gases; contacting said minor amount of combustion gases and particulates associated therewith with catalytic means to convert SO 2 contained therein to SO 3 ; and mixing said minor amount of combustion gases and SO 3 into said main stream of combustion gases and subjecting the mixture formed thereby to electrostatic precipitation; wherein said catalytic means is exposed to said combustion gases within an open gas flow passage whereby particulates freely flow therethrough without substantially interfering with the catalytic conversion of SO 2 to SO 3 by said catalytic means.