Influence of mixing, oxygen and residence time on the SNCR process

• Mixing comes into play only at higher temperatures within the temperature window.
• Oxygen has opposite influence on NO and N2O at lower and higher temperatures.
• NO2 yield is always enhanced by increasing O2.
• Extending residence time shifts the optimum temperature to lower values until 1173 K.
• Our mechanism has good applicability for NOX reduction within tolerable uncertainty.

A laboratory-scale laminar flow reactor coupling chemical reaction and mixing process is used to study the influence of operating conditions (mixing, temperature, oxygen and residence time) on the selective non-catalytic reduction (SNCR) process, in terms of the variations in the concentrations of NO, NH3, NO2 and N2O. As the results indicated, mixing process only comes into play at higher temperatures. At lower temperatures enriched O2 enhanced NO reduction and N2O yield, with more NH3 being consumed. At higher temperatures, increasing O2 inhibited NO reduction and suppressed N2O formation, with the depletion of NH3. NO2 yield was always enhanced by increasing O2, especially at lower temperatures. Extending residence time progressively shifts the optimum temperature for NOX reduction to lower values, but for a sufficiently long residence time, the optimum temperature finally settled at about 1173 K. The detailed mechanism developed in this work gave qualitative and quantitative agreement with our experimental data. Evaluation against several independent works illustrates its capability to predict cases with or without significant mixing process.