Enhanced flue gas damper mixing device

1. A flue gas duct system having a backpass for receiving flue gases from a furnace that operates under various loads, comprising:

at least one heat exchanger disposed within the backpass adapted to extract heat from the flue gases;

a lower flue section being a flue gas conduit coupled to the outlet of the backpass adapted to receive the flue gases;

an upper flue section being a flue gas conduit coupled to downstream flue gas processing devices;

a middle flue section being a flue gas conduit adapted to convey the flue gases from the lower flue section to the upper flue section;

a bypass coupled to the backpass at the middle flue section upstream of an economizer, where the bypass is a flue gas conduit;

an inlet control damper disposed within the lower duct, adapted to adjust the amount of flue gases that flow from the lower flue section to the middle flue section;

a bypass control damper disposed within the bypass duct, adapted to control the amount of flue gases passing from the backpass to the middle duct, thereby bypassing the economizer; and

a damper mixing device for mixing two gas streams in an elongate flue as duct comprising:

a plurality of first rows of louvers, each first row of louvers having a plurality of louvers having adjustable louver vanes pivotable on a pivot about a respective axis, the adjustable louver vanes being positioned in a first direction when at least two gas streams are being received, causing the flue gases passing through the adjustable louver vanes of the plurality of first rows of louvers to be mixed, and positioned in a second direction aligned with the direction of the flue gas when effectively only one gas stream is being received;

wherein each respective row of the plurality of first rows of louvers is spaced from the remaining rows of the plurality of first rows in the longitudinal direction of the flue gas duct;

a plurality of second rows of louvers interleaved, with the plurality of first rows of louvers, each second row of louvers having a plurality of louvers with adjustable louver vanes pivotable on a pivot about a respective axis, the adjustable louver vanes may be positioned in a direction different from the first direction when at least two gas streams are being received causing the flue gases passing through the adjustable louver vanes of the plurality of second rows of louvers to be mixed, and positioned in the second direction aligned with the direction of the flue gas when effectively only one gas stream is being received; wherein each respective row of the plurality of second row of louvers is spaced from the remaining rows of the plurality of second rows of louvers in the longitudinal direction of the flue gas duct; and

a control unit connected to the louvers, adapted to position the louver vanes of the first rows of louvers in the first direction, and the louver vanes of the second rows of louvers in the direction different from the first direction when at least two gas streams are being received, and for positioning the louver vanes of the plurality of first and second rows of louvers in the second direction aligned with the direction of the flue gas when effectively only a single gas stream is being received.

2. The device of claim 1 , wherein the control unit is adapted to position all of the louvers of a given row of the plurality of first rows of louvers at the same angle when at least two oases streams are being received.

3. The device of claim 1 , wherein the control unit is adapted to position all louvers in a given row of the plurality of first rows of louvers in a same direction that is opposite the angle of all louvers of adjacent rows of the plurality of second rows of louvers, when at least two gas streams are being received.

4. The device of claim 1 , further comprising:

a top temperature sensor disposed in the upper flue section in communication with the control unit and adapted to measure a temperature in the upper flue section and to provide an indication of the measured temperature to the control unit to determine an amount to open inlet control damper and bypass control damper.

5. The device of claim 4 , further comprising:

a bottom temperature sensor disposed upstream of the inlet control damper, in communication with the control unit, and adapted to measure a temperature of the flue gases in the lower flue section.

6. The device of claim 5 , further comprising:

a bypass temperature sensor disposed upstream of the bypass control damper, in communication with the control unit, and adapted to measure a temperature of the flue gases in the bypass duct and to provide an indication of the measured temperature to the controller.

7. The device of claim 1 , further comprising:

a first pressure sensor upstream of the damper control mixing device, and

a second pressure sensor downstream of the damper control mixing device, the

pressure sensors adapted to measure pressure drop across the damper control mixing device and to provide the pressure drop measurement to control unit.

8. The device of claim 1 wherein:

the control unit is further adapted to interactively change the louver positions under varying boiler loads to determine louver angles that optimize both the pressure drop and maximize mixing effectiveness.

9. The device of claim 1 wherein:

the louvers within a row of the plurality of first rows of louver may be adjusted to different positions.

10. The device of claim 1 , wherein each respective axis of the pivot of the vanes of the plurality of first rows of louvers is different, and each respective axis of the pivot of the vanes of a respective second row of the plurality of second rows of louvers is different.