Flue gas stream bypass during selective catalytic reduction in a power plant

A system comprising:

• a selective catalytic reactor;
• where the selective catalytic reactor is located downstream of a furnace that generates flue gases;
• the selective catalytic reactor being operative to reduce nitrogen oxides to nitrogen;
• a bypass line;
• the bypass line being 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;
• and
• a second control damper that is disposed at an inlet to the bypass line;
• where the first control damper and the second control damper interact to divide the flue gas stream between the selective catalytic reactor and the bypass line in ratio that is effective to reduce the amount of sulfur trioxide released from the system to a desirable value, further comprising a SO3 analyzer and a controller, where the SO3 analyzer is disposed downstream of the selective catalytic reactor and where the controller is in operative communication with the SO3 analyzer, and the first control damper and the second control damper.