2013 Volume 55 Issue 173 Pages 278-284
The removal of hydrogen in the off-gas from fuel cells in a safe manner is desirable. Hydrogen oxidation by an atmospheric non-equilibrium plasma is a promising technique for the off-gas treatment. In the present research, characteristics of NOx formation in hydrogen oxidation by the pulsed plasma were investigated to determine an optimum oxidation condition in H2/O2/N2 gas mixture. The applied voltage, repetition rate, gas flow rate, and equivalence ratio were varied. NOx concentrations generally increased with an increase in the energy density and with a decrease in the equivalence ratio. To understand the reaction mechanism of NOx formation in hydrogen oxidation, a reaction kinetic study was carried out. The chemistry was resolved into separate contributions from radiolysis processes and gas phase reactions. N radical generated by electron impact reactions in the pulsed plasma and molecular oxygen play an important role for NOx formation (N + O2 → NO + O). At high equivalence ratios, NOx level was strongly reduced by gas phase reaction of N + NO → N2 + O. It was found that the equivalence ratio was the most dominant factor to control NOx concentration in hydrogen oxidation by the pulsed plasma. An energy efficiency of 0.26 g-H2/J and a NOx emission of 5 ppm was attained at an equivalence ratio of 2.0.
