Chemical Engineering Journal Advances (Aug 2023)
Removal of NOx using ozone injection and subsequent absorption in water
Abstract
In nuclear reprocessing plant reduction of the nitric acid from the high level radioactive liquid waste is accomplished by the addition of formaldehyde. A significant amount NOx is generated during this conventional acid killing process. In this case NO oxidation followed by NO2 absorption is considered as a suitable option for NOx eradication, which also produces reusable nitric acid. Hence, investigations to explore the NO oxidation in the presence of O3 have been carried out for a relatively large system where the total flow rate of gas stream was 800 SLPM (52.4 m3/ h at 25 °C) and the concentration of NO was 480 ppm. It was observed that the concentration of NO decreases with the increase in the concentration of O3 added. A mathematical model has also been developed to predict the concentration of the gaseous components at the exit of the ozonization chamber. Model calculation shows that the reaction between NO and O3 is completed within fraction of a second. Further investigation on the absorption of NO2 in water was carried out by passing the exhaust gas through a scrubber. The absorption of NO2 in water leads to the formation of NO. An attempt has been made to enhance the performance of the water scrubber by injecting ozone into the gas phase during NO2 absorption. The model prediction reveals that N2O5 is the ultimate fate of the NO2 in the presence of O3. The evolution of N2O5 can be considered as two-step process. Reaction between NO2 and O3 is slow and the rate controlling step. On the contrary NO3 reacts quite rapidly with remaining NO2 and produces N2O5.
