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EVALUATION OF DESIGN ALTERNATIVES FOR AN SCR SYSTEM DOWNSTREAM OF A SIMPLE CYCLE COMBUSTION GAS TURBINE

A recent CFD study was conducted to evaluate various design options for the placement of a Selective Catalytic Reduction (SCR) system downstream of a nominal 200 MW Simple Cycle combustion gas turbine. The average temperature of the flue gas leaving the turbine is in excess of 1125 °F. In this application, tempering air is mixed with the flue gas stream to reduce the temperature of the gas prior to the SCR catalyst beds. CO catalyst is optionally installed downstream of the flue gas mixing location to reduce carbon monoxide emissions in the flue gas. An ammonia injection grid is installed before the NO x catalyst to reduce nitrogen oxide (NO x ) emissions in the flue gas. The efficiency of the NO x removal process is dependent on the uniformity of flue gas velocity, gas temperature, NH 3 to NO x concentration ratio at the catalyst inlet. A detailed CFD design analysis was conducted to evaluate various options for the injection of tempering air into the flue gas stream and to optimize flow distribution upstream of the CO and NO x catalyst beds. This paper describes Riley Power Incorporated (Riley Power), a Babcock Power Inc. company, evaluation of various design options to achieve the optimal flow conditions for best operation of the current simple cycle SCR system. A number of flow control devices, including Delta Wing ® mixers were evaluated in combination with different injection methods for the tempering air. Inlet conditions were based on the flow, gas composition and temperature profiles at the combustion turbine outlet provided by the turbine manufacturer. Velocity and temperature profiles at particular sections of interest were monitored for each studied configuration. Various locations and designs for the mixing devices were evaluated and compared for mixing optimization and local areas of peak velocities. The different configurations, modeling results and their impact on flue gas velocity and temperature distribution are discussed in detail.