Alden simulated the planned Kansas City Power and Light Iatan Unit 2 (POWER Magazine’s 2011 plant of the year) Selective Catalytic Reduction Systems (SCR) to maximize the NOx removal efficiency. An SCR operates by injecting a reagent, typically ammonia (NH3), into the flue gas stream, and then catalyzing a reaction to convert the NO2 and NO3 into nitrogen and water. For optimum system operation, the distribution of the NOx, reactant, gas velocity, and temperature must be very uniform entering the catalyst to maximize the reaction and prolong catalyst life. Upstream collection of large particle ash (LPA), and the distribution of fine ash at the inlet face of the first catalyst are also important components of SCR operation that must be considered to inhibit premature outages caused by pluggage.
Physical and computational flow modeling techniques were used to develop and optimize duct and SCR flow controls, ammonia injection grid, mixing devices, and ash handling devices to achieve best performance targets for NOx removal. The new connecting ductwork from the retrofit SCR to the existing air preheaters was also included in the study to provide flow controls designs to optimize air preheater performance. The models simulated the field gas velocities, temperatures, pressure losses, NOx concentrations, NH3 injections, and ash particulate transport and removal.