System and method for mixing tempering air with flue gas for hot SCR catalyst

A simple cycle heavy-duty gas turbine system, comprising:

• a mixing system disposed in an exhaust processing system of the simple cycle heavy-duty gas turbine system, wherein the mixing system comprises:
• a first mixing module comprising a first grid having a first plurality of rotary turbulators configured to swirl cooling air, an exhaust stream generated by a heavy-duty gas turbine engine of the simple cycle heavy-duty gas turbine system, or both, in a first swirl direction;
• and
• a second mixing module comprising a second grid having a second plurality of rotary turbulators configured to swirl the cooling air, the exhaust stream, or both, in a second swirl direction, wherein the first mixing module, the second mixing module, or both are disposed within a transition duct of the exhaust processing system such that each rotary turbulator of the first and second plurality of rotary turbulators is arranged at a different position relative to another rotary turbulator along a dimension of the respective grid, wherein the dimension is crosswise to a flow direction through the exhaust processing system, and wherein each rotary turbulator of the first and second plurality of rotary turbulators comprises a shaft configured to rotate the rotary turbulator about a longitudinal axis of the exhaust processing system.

A method of processing exhaust gas in a simple cycle gas turbine system, comprising:

• flowing an exhaust stream from a gas turbine engine and into a transition section of an exhaust processing system;
• injecting cooling air into a flow of the exhaust stream in the transition section using an air injection system comprising a plurality of air injection tubes configured to inject the cooling air;
• swirling the exhaust stream, or the cooling air, or both, in the transition section of the exhaust processing system using a mixing system having an array of mixing modules, wherein each mixing module of the array of mixing modules comprises a grid having a plurality of rotary turbulators configured to swirl the exhaust stream, the cooling air, or both in a first direction, a second direction, or both, and wherein swirling the exhaust gas, the air, or both mixes and facilitates heat transfer between the exhaust steam and the cooling air within the exhaust processing system to generate a cooled exhaust gas, wherein each rotary turbulator of the plurality of rotary turbulators comprises a shaft configured to rotate the respective rotary turbulator;
• directing the cooled exhaust gas to a selective catalytic reduction (SCR) system;
• and
• reducing a level of nitrogen oxides (NOx) in the cooled exhaust gas using the SCR system.