NOx removal with efficient recycling of NO2 from iron-ore sintering flue gas: A novel cyclic adsorption process.

Conventional flue gas nitrogen oxides (NOx) abatement technologies commonly convert NOx into harmless compounds, while less effort has been made to recycle NO2 as a profitable chemical in many industries. Towards this end, adsorption is a promising technology for which an advanced technique for NO2 desorption and efficient sorbent regeneration provides the key step for success in practical applications. This work reports a novel cyclic adsorption process for NOx removal with recycling of NO2 from iron-ore sintering flue gas of a steel plant. This process using self-prepared and validated pelletized Na-ZSM-5 zeolites as low-cost sorbents involves NOx catalytic adsorption and reversible desorption using multiple hot gas circulations (GC) within the enclosed fixed bed followed by scavenging and purge at mild conditions. In comparison to conventional cyclic processes, greater amount of recyclable NO2 was obtained, rendering the NOx recovery of >92% and the mean NO2 concentration of >2% significantly enriched from original 20 ppm in feed gas. A robust adsorption-desorption performance with appreciable NOx working capacity was achieved for up to 16 cycles. The key role of the segmentation of GC in boosting NOx regenerability was addressed, providing an economical three-tower strategy for continuous NO2 production for practical use.