Ozone injection-chemical hybrid process for simultaneous removal of NO and SO from ammonia-coal co-firing exhaust gas

• No effect of SO 2 on NO oxidation by O 3 is demonstrated even high SO 2 /NO ratio. • Plasma-chemical hybrid process reduces NO x from 15 to <10 ppm. • NO x removal efficiency increases as the SO 2 concentration increases. • The removal efficiencies of SO 2 of 99% and NO x of 45% are obtained. Ammonia-coal co-firing for thermal power generation has recently attracted considerable attention as a game-changer for decarbonization. However, its combustion with a 20% or higher ammonia (NH 3 ) ratio emits higher amounts of nitrogen oxides (NO x ) than coal-fired combustion, surpassing the denitration capabilities of existing selective catalytic reduction (SCR) systems, resulting in excessing the regulation value determined by agreements on environmental conservation. To eliminate the NO x remaining after SCR, we propose a plasma-chemical hybrid process (PCHP) as a NO x treatment technology that can be easily retrofitted into existing exhaust gas treatment equipment. PCHP consists of NO oxidation using plasma ozonizers and NO 2 reduction by existing desulfurization equipment. Assuming the ozone injection in the flue gas duct between the SCR and desulfurization equipment, we conducted NO oxidation and the simultaneous removal of NO x and sulfur oxides (SO x ) for a simulated flue gas comprising low-concentration NO and high-concentration sulfur dioxide (SO 2 ). This was achieved using an ozone injection tower that simulated the flue gas duct and a calcium carbonate-slurry based SO 2 absorption tower that simulated the desulfurization equipment. The results show that even under conditions containing SO 2 at a concentration 46-fold higher than that of NO, the NO oxidation by O 3 was achieved without the effect of SO 2 . When the SO 2 removal efficiency reached 99%, which is equivalent to that of an actual facility, an NO x removal efficiency of 45% was attained. Therefore, an NO x removal efficiency of 45% can be also expected for an actual facility, contributing to further reductions in NO x .