A simple-cycle gas turbine system includes an injection system including a plurality of injection tubes that may inject a fluid into a duct of an exhaust processing system that may process exhaust gas generated by a gas turbine engine. The exhaust processing system includes a selective catalytic reduction (SCR) system that may reduce a level of nitrogen oxides (NOx) within the exhaust gas; and a mixing system positioned adjacent to the plurality of injection tubes and within the exhaust processing system. The mixing system includes a mixing module having a plurality of turbulators that may swirl the fluid, or the exhaust gas, or both, in a first swirl direction to encourage turbulent flow along an axis of the exhaust processing system and thereby facilitate mixing between the fluid and the exhaust gas.