Single seam duct corner

A preheater system for preheating combustion air for a boiler with flue gas exiting the boiler, the preheater system comprising:

• an air preheater having a substantially circular cross section and a rotor bearing a heat transfer mass which is rotatable through a flue gas sector for absorbing heat from the flue gas and an air sector for releasing heat to the combustion air;
• a plurality of ducts, each of the ducts having a substantially rectangular cross section, the ducts including a cool air duct adapted for carrying cool combustion air to the air preheater, a hot air duct adapted for carrying heated combustion air from the air preheater to the boiler, a hot flue gas duct adapted for carrying hot flue gas from the boiler to the air preheater, and a cold flue gas duct adapted for carrying cooled flue gas from the air preheater;
• and
• a transition system including a first transition element disposed intermediate the cool air duct and the air sector of the air preheater, a second transition element disposed intermediate the hot air duct and the air sector of the air preheater, a third transition element disposed intermediate the hot flue gas duct and the flue gas sector of the air preheater, and a fourth transition element disposed intermediate the cold flue gas duct and the flue gas sector of the air preheater, each of the transition elements including an inner sidewall, an outer sidewall, and first and second end walls, the outer sidewall and the first and second end walls defining first and second transition corners, each of the transition corners comprising first and second flow deflectors, each of the flow deflectors having an outer terminal edge and first and second side edges extending laterally from the terminal edge to an inner point, the first side edge of the first flow deflector being mounted to the second side edge of the second flow deflector, the second side edge of the first flow deflector and the first side edge of the second flow deflector being mounted to the air preheater.