Experimental study and kinetic modeling on the effects of HBr on CO and NO emissions during CO/NH3 co-combustion

Abstract

Bromine released from fossil fuel combustion, particularly in the form of HBr, is a significant atmospheric pollutant and a well-known inhibitor in combustion systems. However, its precise reaction mechanism during CO/NH₃ co-combustion remains unclear and highly sensitive to reaction conditions. To address this research gap, this work conducts an experimental and kinetic modeling study to investigate the effect of HBr on CO and NO emissions under simplified combustion conditions. Using an entrained flow reactor and detailed kinetic analysis, we examined HBr’s influence across a range of temperatures and concentrations. The results show that HBr strongly inhibits CO oxidation and NO formation at lower temperatures (1023–1123 K) by scavenging H radicals via reaction R272 (HBr + H = Br + H₂). This effect, however, is highly temperature-dependent: at higher temperatures (up to 1223 K), the influence shifts to NO promotion, attributed to the kinetically favored Br-species reaction R302 (Br + HNO = HBr + NO). This study provides critical insights into the competing radical mechanisms governing halogen-pollutant interactions, thereby advancing the mechanistic understanding of HBr’s temperature-dependent effects on pollutant emissions during CO/NH₃ co-combustion.

Novelty and Significance Statement

This work focuses on the industrially relevant CO/NH₃ co-combustion system, a research niche less explored in halogen combustion chemistry, and combines entrained flow reactor experiments with multi-dimensional kinetic analyses (ROP, sensitivity, radical profiling) to uncover the distinct temperature-dependent dual effects of HBr: potent inhibition of CO oxidation and NO formation at 1023–1123 K via H-radical scavenging (R272: (H + HBr = H2 + Br)), and a shift to NO promotion above 1173 K driven by kinetically dominant R302: Br + HNO = NO + HBr. It clarifies the radical competition mechanism of bromine-containing species in halogen-nitrogen-carbon coupling reactions, furnishing novel kinetic insights into HBr’s regulatory role in denitration-related combustion processes. The findings further provide a targeted theoretical basis for optimizing pollutant control strategies in bromine-containing combustion systems, supplementing the current understanding of halogen-involved combustion chemistry.