A system comprising: a selective catalytic reactor arranged to be located downstream of a furnace that generates flue gases, the selective catalytic reactor being operative to reduce nitrogen oxides to nitrogen and to promote oxidation of sulfur dioxide to sulfur trioxide; a bypass line in fluid communication with the selective catalytic reactor , the bypass line contacting an input line to the selective catalytic reactor , where the bypass line is adapted to handle a volume of flue gases that are diverted from the selective catalytic reactor ; a first control damper disposed at an inlet to the selective catalytic reactor ; a second control damper disposed in the bypass line , where the first control damper and the second control damper are arranged to interact to divide the flue gas stream between the selective catalytic reactor and the bypass line in a ratio that is effective to reduce an amount of sulfur trioxide (SO 3 ) released from the system to a desirable value, the desirable value being less than or equal to 5 ppm based on the total volume of the flue gas stream; an SO 3 analyzer disposed downstream of the selective catalytic reactor and arranged to measure the amount of sulfur trioxide (SO 3 ) in the flue gas stream; and a controller in operative communication with the SO 3 analyzer , the first control damper and the second control damper , the controller arranged to facilitate adjusting the first and second control dampers to determine the percentage of the flue gas stream that is directed to the selective catalytic reactor and the percentage that is directed to the bypass line thereby bypassing the selective catalytic reactor . a selective catalytic reactor arranged to be located downstream of a furnace that generates flue gases, the selective catalytic reactor being operative to reduce nitrogen oxides to nitrogen and to promote oxidation of sulfur dioxide to sulfur trioxide; a bypass line in fluid communication with the selective catalytic reactor , the bypass line contacting an input line to the selective catalytic reactor , where the bypass line is adapted to handle a volume of flue gases that are diverted from the selective catalytic reactor ; a first control damper disposed at an inlet to the selective catalytic reactor ; a second control damper disposed in the bypass line , where the first control damper and the second control damper are arranged to interact to divide the flue gas stream between the selective catalytic reactor and the bypass line in a ratio that is effective to reduce an amount of sulfur trioxide (SO 3 ) released from the system to a desirable value, the desirable value being less than or equal to 5 ppm based on the total volume of the flue gas stream; an SO 3 analyzer disposed downstream of the selective catalytic reactor and arranged to measure the amount of sulfur trioxide (SO 3 ) in the flue gas stream; and a controller in operative communication with the SO 3 analyzer , the first control damper and the second control damper , the controller arranged to facilitate adjusting the first and second control dampers to determine the percentage of the flue gas stream that is directed to the selective catalytic reactor and the percentage that is directed to the bypass line thereby bypassing the selective catalytic reactor . <EOS>