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

Conventional flue gas nitrogen oxides (NO_x) abatement technologies commonly convert NO_x 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 NO_x 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 NO_x 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 NO_x 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 NO_x working capacity was achieved for up to 16 cycles. The key role of the segmentation of GC in boosting NO_x regenerability was addressed, providing an economical three-tower strategy for continuous NO₂ production for practical use.