Homogeneous Oxidation of Volatile Nitrogen (NH_{3}, HCN) to Nitrogen Oxides: A Modeling Study of the Effect of Alkali Vapors


Abstract: The effect of alkali vapors in the combustion of different types of Scandinavian fuels, i.e. Finnish black liquor, Swedish wood and Danish straw, was studied based on detailed chemical kinetic modeling. Two H/C/O/N/Na/K mechanisms consisting of about 350 reactions between 60 chemical species were utilized and validated with available experimental data from the literature. The agreement with the experimental results was satisfactory. The results demonstrated that the alkali species studied, i.e. Na and K, promote the NO_x reduction in the air staged or non-staged combustion systems. The presence of alkali metals increased the optimum temperature from ca. 1073-1173 K (no alkali cases) to ca. 1273-1373 K (alkali cases) due to the removal of the radicals via the following sequence: NaOH + H \to Na + H_2 O {R254} (1) Na + O_2 + M \to NaO_2 + M {R242} (2) NaO_2 + OH \to NaOH + O_2 {R260} (3) ------------------------------------- H + OH \to H_2 O (4) which leads to a net formation of water (H_2O) from H and OH. The same trend was observed for K chemistry. Sensitivity and reaction path analysis was applied to investigate the most crucial reactions on the predictions.

Keywords: Alkali, NO_x reduction, Chemkin, Kinetic modeling

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