Detailed Modeling of the Effects of K/Na Additives on the Thermal DeNO_x Process

摘要

A reduced mechanism simplified from a detailed chemical kinetics mechanism containing N/H/O/K/Na elements was developed and validated in this paper. When the reduced mechanism was integrated into computational fluid dynamics (CFD) software, the effect of potassium and sodium additives on the selective non-catalytic reduction (SNCR) thermal DeNO_x process was simulated. The simulation results were compared to those of experiments under different oxygen concentrations, normalized stoichiometric ratios (NSRs) of the N agent/NO, and alkali metal additive concentrations within the temperature range from 1023 to 1523 K, and the simulation results coincided qualitatively with those of the experiment in an entrained flow reactor. The alkali metal additives did not change the effects of the oxygen concentration and NSR on the SNCR process: a conversion temperature point exists at about 1173-1223 K; below die conversion temperature point, a higher oxygen concentration can promote the effect of SNCR, while above the conversion temperature point, the efficiency will be reduced; and a higher NSR is beneficial for NO reduction, but its effect becomes less obvious with the increase of the reducing agent. The alkali metal additives extend the "temperature window" toward a lower temperature by about 50-100 K with more OH and NH_2 radical production, and the effect of K additives is less obvious than that of Na. However, the promoting effect of the K additive cannot be well-simulated because of the lack of a suitable mechanism. A K chemistry mechanism should be optimized on the basis of its effect on the SNCR process. The K or Na concentration almost has no influence on the effect of alkali metal additives on the thermal DeNO_x process when the K or Na concentration is beyond a certain value.