The removal of NO by low-temperature O3 oxidation

The features of a process removing NO at low temperatures by O3 are examined. The process is modeled employing “full” chemistry and simulated in a perfectly stirred reactor (PSR). A generic reaction set that also has implications for the nighttime removal of NOx and O3 from the atmosphere is collated and utilized. The issues addressed include (1) the percentage of NO representative of flue gas that can be removed by the process under various parametric conditions, and the corresponding range of ozone demand for high NO removal; (2) the mechanisms of NO conversion; and (3) the effect of temperature on NO removal. It is determined that the removal of NO due to ozone oxidation occurs largely through a single reaction NO + O3 ↔ NO2 + O2. The oxidation of NO to NO2 is favored at lower temperatures, and the NO inlet mole fraction can be reduced by two orders of magnitude at the outlet in the absence of high SO levels in the feed stream even with moderate ozone input. However, the presence of SO assists in the re-conversion of NO2 to NO. Furthermore, higher residence times do not necessarily imply larger NO removal. If the PSR is operated as a locally homogeneous volume analogous to nighttime atmospheric conditions OH radicals become a significant sink for NO, and reactions of hydroxyl with CO and CH4 assume secondary significance.