Experimental characterization of enhanced SNCR process with carbonaceous gas additives

Carbonaceous gases such as CO and alkanes are commonly used as additives to enhance the selective non-catalytic reduction (SNCR) performance due to their high reducibility. This study compared the effect of CO and CH₄ on NO reduction in a tubular reactor with simulated flue gas. The enhancement of C₃H₈ on SNCR process was tested at extremely low temperature, i.e. 650 °C. Experimental results suggested that reactions between NH₃ and SO₂ were favored at low temperatures and the competition for NH₃ between SO₂ and NO was influenced by gas additives. A maximum downward shift of 25 °C and 100 °C in temperature window for 50% NO reduction efficiency was obtained with the addition of CO and CH₄, respectively. Considerable CO emission was observed with addition of CH₄. The addition of CH₄ contributed to the formation of a self-accelerating reaction route within NO/O₂/NH₃ SNCR reaction system. NO₂ produced from NO accelerates the oxidation of CH₄ to CO, while the oxidation of CH₄ returns to enhance the NO reduction globally. Optimal NO reduction of 44% was achieved with addition of C₃H₈ at 650 °C. Substantial portion of C₃H₈ was partially oxidized to CO and the remaining was converted into C₂H₄ and C₃H₆ during the SNCR process. Oxidative dehydrogenation of C₃H₈ was involved. High reactivity of C₃H₆ and C₂H₄ favored the further oxidation and cracking to produce CO. These differences in oxidation behavior significantly influence the promotion capacities of CO, CH₄ and C₃H₈ for NO reduction.