Efficiency Improvement in Reactive Absorption of Nitrogen Oxides

This study is focused on reactive absorption of nitrogen oxides created during calcium nitrate fertilizer production. A functional mathematical process model was set up to verify the process by experimental data and to devise modifications of a real plant with this technology. Suggestions for nitrogen oxide removal efficiency improvement, including changes in operational parameters and plant layout were simulated in Aspen Plus, to achieve compliance with the European legislative emission limit of 300 ppm (mg/m3) of NOx in the off-gas released to the atmosphere. Neither of the suggested process modifications, be it an increase in column packing specific area, increase in packing height, liquid recycles cooling to ambient temperature or make-up absorbent flow rate increase led to sufficient NOx concentration decrease. Addition of a H2O2 solution into the second column was proposed to scavenge the remaining NO as it contributes mostly to the overall NOx emissions. Simulation results indicate this as a viable option to both meet the legislative criteria and to avoid liquid streams' contamination so they can be reprocessed instead of being dealt with as waste.