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

1. 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 SO 3 analyzer and a controller, where the SO 3 analyzer is disposed downstream of the selective catalytic reactor and where the controller is in operative communication with the SO 3 analyzer, and the first control damper and the second control damper.

2. The system of claim 1 , further comprising a first isolation damper disposed upstream of the first control damper and another isolation damper disposed upstream of the second control damper.

3. The system of claim 2 , where the controller is in operative communication with the first isolation damper and the isolation damper that is disposed upstream of the second control damper.

4. The system of claim 2 , where periodic sulfur trioxide measurements are manually made downstream of the selective catalytic reactor and where the results are used to manually or automatically adjust the first control damper and the second control damper.

5. The system of claim 1 , where the selective catalytic reactor is smaller in size than a selective catalytic reactor disposed in a comparative system that does not have the bypass line, the first control damper and the second control damper.

6. The system of claim 1 , where the selective catalytic reactor receives up to 30 volume percent less flue gas than a selective catalytic reactor disposed in a comparative system that does not have the bypass line, the first control damper and the second control damper.

7. The system of claim 1 , where the desirable value is less than 5 ppm based on the total volume percent of the flue gas stream.

8. A method comprising:

discharging a flue gas stream from a furnace to 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; and

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;

dividing the flue gas stream between the selective catalytic reactor and the bypass line in a ratio that is effective to reduce the amount of sulfur trioxide released from the system to a desirable value.

9. The method of claim 8 , further comprising the flue gas stream emanating from the selective catalytic reducer by wet chemistry and where the dividing of the flue gas stream is accomplished manually.

10. The method of claim 8 , where the dividing of the flue gas stream is accomplished via automation by an in-line analyzer and a controller.

11. The method of claim 8 , further comprising discharging an entire portion of the flue gas stream that contains undesirable contaminants via the bypass line.