System and method for reducing back pressure in a gas turbine system

1. A power plant system, comprising:

a power plant exhaust stack having an exhaust duct configured to flow an exhaust gas; and

an air injection system coupled to the exhaust duct, wherein the air injection system comprises:

a sensor configured to sense a pressure condition indicative of a back pressure associated with a flow of the exhaust gas through the exhaust duct;

a controller having instructions to receive, from the sensor, pressure data relating to the back pressure, and to control the air injection system, based at least in part on the pressure data, to reduce the back pressure; and

a first air injector configured to, upon instruction from the controller, inject air into the exhaust duct to assist the flow of the exhaust gas through the exhaust duct.

2. The power plant system of claim 1 , comprising an exhaust duct module having the air injection system coupled to the exhaust duct, wherein the air injection system comprises a plurality of air injectors including the first air injector.

3. The power plant system of claim 1 , comprising a compressor configured to supply at least a first portion of compressed air to the air injection system such that the first air injector of the air injector system injects compressed air into the exhaust duct to assist the flow of the exhaust gas through the exhaust duct.

4. The power plant system of claim 3 , comprising a turbine engine that expels the exhaust gas into the exhaust duct.

5. The power plant system of claim 4 , comprising a combustor fluidly coupled with, and between, the compressor and the turbine, wherein the combustor receives a second portion of the compressed air from the compressor, wherein the combustor combusts a fuel together with the second portion of the compressed air to generate the exhaust gas, and wherein the turbine receives the exhaust gas from the combustor.

6. The power plant system of claim 1 , wherein the air injection system comprises a second air injector, wherein the first and second air injectors have different sizes, different shapes, different depths into the exhaust duct, or a combination thereof.

7. The power plant system of claim 1 , wherein the first air injector comprises an air blade.

8. The power plant system of claim 1 , wherein the first air injector comprises an air nozzle.

9. The power plant system of claim 1 , wherein the air injection system comprises a rake disposed in the exhaust duct, and the rake comprises the first air injector.

10. The power plant system of claim 1 , wherein the air injection system comprises a plurality of rakes disposed in the exhaust duct, and at least one rake of the plurality of rakes comprises a plurality of air injectors having the first air injector.

11. The power plant system of claim 1 , wherein the first air injector is generally flush with an inner surface of the exhaust duct.

12. The power plant system of claim 1 , wherein the first air injector protrudes into the exhaust duct.

13. The power plant system of claim 1 , wherein the air injection system comprises a first injection stage having the first air injector and a second injection stage having a second air injector, wherein the first and second injection stage are disposed at different axial positions along the exhaust duct.

14. The power plant system of claim 1 , wherein the air injection system comprises a controller having instructions to control air flow through the air injection system into the exhaust duct to reduce back pressure associated with flow of the exhaust gas through the exhaust duct.

15. The power plant system of claim 1 , wherein an angle of the first air injector with respect to the flow of the exhaust gas, and the corresponding downstream direction, is adjustable.

16. A land-based system comprising: a controller having instructions to: receive, from a sensor, pressure data relating to a back pressure associated with a flow of exhaust gas through an exhaust duct of an exhaust stack of a power plant; control, based at least in part on the pressure data, an air flow through an air injection system into the exhaust duct to reduce the back pressure associated with the flow of the exhaust gas through the exhaust duct, wherein the air flow is directed into the exhaust duct in a downstream direction, and the downstream direction of the air flow causes the air flow to energize the flow of the exhaust gas through the exhaust duct.

17. The land-based system of claim 16 , wherein the controller has instructions to control the air flow from a compressor of a gas turbine engine to the exhaust duct downstream of a turbine of the gas turbine engine.

18. The land-based system of claim 17 , comprising the gas turbine engine.

19. The land-based system of claim 17 , comprising:

the exhaust duct having the air injection system; and

the sensor.

20. The land-based system of claim 16 , wherein the controller has instructions to control a plurality of stages of the air injection system.

21. A method, comprising: sensing, via a sensor disposed within an exhaust duct of an exhaust stack of a power plant, a pressure condition indicative of a back pressure associated with a flow of an exhaust gas through the exhaust duct; communicating pressure data associated with the back pressure from the sensor to a controller; and controlling, via the controller and based at least in part on the pressure data, an air flow through an air injection system into the exhaust duct to reduce the back pressure; and directing the air flow into the exhaust duct in a downstream direction, wherein the downstream direction of the air flow causes the air flow to energize the flow of the exhaust gas through the exhaust duct.

22. The method of claim 21 , comprising:

receiving the air flow from a compressor of a gas turbine engine;

routing the air flow through the air injection system into the exhaust duct downstream of a turbine of the gas turbine engine; and

reducing the back pressure with the air flow.