Chemical Kinetics Modeling and Analysis of Monomethylamine for Power Plants Selective Non-Catalytic Reduction (SNCR) Systems

A study was performed to investigate monomethylamine (MMA) as an alternative or supplementary reagent for selective non-catalytic reduction (SNCR) of nitrogen oxides (NOx) for power plants especially the coal-fired type. A detailed chemical kinetics mechanism for MMA, related to the SNCR NOx reduction process, was modeled using a simplified plug flow reactor (PFR) approach using the CHEMKIN software. Model validation results were in line with reported experimental results. A model sensitivity analysis showed that the normalized MMA/NO stoichiometric ratio (NSR) and the initial NOx concentration are the most critical parameters that significantly affect MMA-based process performance. Additionally, a reduced reaction mechanism and its mechanism tree for this particular process are proposed, consisting of only 18 reactions and 21 species. Simulation comparisons with three other reagents (ammonia, urea, and cyanuric acid), under similar process conditions, indicate that MMA-based SNCR NOx reduction process has a superior performance at much lower temperatures (under 800 K) than conventional SNCR processes, with the added benefit that it does not suffer from ammonia slip problems. The MMA-based SNCR NOx removal system could be applied in cascade mode with other post-combustion NOx removal approaches to extend NOx control to lower temperatures and eliminate the temperature window limitation and potential ammonia slip of conventional SNCR systems. The cascade design is a perfect solution for coal power plants especially at partial load modes of operation which provides more flexibility in performance for such plants. The results of the simulations in this study show that the potential of MMA for SNCR NOx reduction systems at full-scale power plants has significant merit.