Nitrogen-diluted ammonia SNCR for enhanced NOx removal in a ceramic roller kiln

Abstract

This study investigates the application of nitrogen-diluted ammonia injection in Selective Non-Catalytic Reduction (SNCR) systems to enhance NOx removal efficiency in a high-temperature, oxygen-abundant ceramic roller kiln environment. Traditional SNCR systems using pure ammonia face challenges such as premature ammonia oxidation, leading to low De-NOx efficiency and secondary pollution. By introducing nitrogen gas as a diluent, the local oxygen concentration and reaction temperature are reduced, mitigating ammonia combustion and prolonging its availability for NOx reduction. Experimental tests were conducted in an industrial ceramic roller kiln, focusing on the kiln tail zone (850–1100°C, 15% O₂). Results demonstrate that nitrogen dilution significantly improves SNCR performance: at 150 slpm ammonia and 200 slpm nitrogen, the highest De-NOx efficiency reached 86%, reducing NOx emissions from 994 mg/m³ to 143 mg/m³ (at 18% O₂). However, increased ammonia slips and nitrous oxide (N₂O) emissions were observed, necessitating secondary mitigation strategies. Broadband imaging confirmed that nitrogen suppresses ammonia flame formation, enhancing reagent utilization. The study also highlights the method’s applicability in other oxygen-abundant industrial scenarios, such as gas turbines, where SCR integration is limited. These findings provide critical insights for optimizing SNCR in decarbonizing high-temperature industrial processes. It should be clarified that this roller kiln is equipped with an SCR unit, which serves as the primary technique for flue gas treatment. The SCR operates independently, without reliance on SNCR, or with minimal assistance from SNCR through small amounts of pure ammonia injection at kiln head. Consequently, N₂O and NH₃ slip do not pose a concern.