In-duct flue gas conditioning system

In a system for conditioning flue gas generated by a boiler furnace prior to its emission to the atmosphere, including conduit means for conducting a flow of flue gas from said boiler furnace to the atmosphere and an electrostatic precipitator located in said conduit means for electrostatically removing particulate matter entrained in the flue gas, the improvement comprising:

• an assembly arranged upstream of the electrostatic precipitator for converting a portion of sulfur dioxide contained in the flue gas flow to sulfur trioxide, said conversion assembly including catalytic conversion means having an operative position wherein a portion of the flue gas flow passes through said catalytic conversion means for converting a portion of the sulfur dioxide contained in the flue gas flow to sulfur trioxide, and an inoperative position wherein the flue gas flow does not pass through said catalytic conversion means, and operating means for providing said catalytic conversion means in said operative and inoperative positions,
• said catalytic conversion means including one or more SO.sub.2 /SO.sub.3 converters comprising a foraminous ceramic substrate forming a plurality of open and generally parallel flow paths for flue gas provided with a SO.sub.2 /SO.sub.3 catalyst material.