Nitrogen oxides pre-ozonation in flue gases from phosphate rock digestion

•Pre-ozonation of off gases from phosphate rock digestion is a promising FGT technique.•It was proven that it is an efficient and safe way to intensify NOx removal.•The required molar ratio O3/NOx equal to 1 was sufficient in pilot scale NOx removal.•It was proven in the lab-scale that presence of H2O enhanced NOx conversion to N2O5.

In this study we demonstrate both laboratory and pilot scale results for NOx ozonation of the simulated and real flue gases from the NPK fertilizer production plant. The off-gases from phosphate rock digestion process contain nitrogen oxides NOx, H2O vapor, hydrogen fluoride (HF) and silicon tetra-fluoride (SiF4). The usefulness of the pre-ozonation as a method for the intensification of NOx removal was proved. The required molar ratio O3/NOx together with the residence time and the influence of water vapor were determined. The O3/NOx ratio turned out to be around 1 for the industrial process. The presence of water vapor enhances the conversion rate from 5% to 63% for residence time lower than 1 s.We had confirmed for the first time that the pre-ozonation of flue gases from phosphate rock digestion process is a viable solution for the NOx removal.