Optimizing Combustion Process: The Impact of Flame Zone Air Supply on Emissions and Performance in Pellet Boiler

Biomass combustion is a widely used renewable option for a small-scale heat and power, but incomplete burnout and pollutant formation remain challenges in boilers without optimized air staging. In this study, is investigated how controlled transport of air into the flame zone, implemented with an auxiliary tertiary system, affects performance and emissions in a bottom-fed pellet boiler. Tests were performed at constant fuel feed and primary/secondary airflow, with tertiary air varied between 0 and 15.8 m3/h. An airflow of about 8.9 m3/h proved optimal, giving the highest thermal output, a more uniform temperature distribution, and a nearly twentyfold reduction in CO emissions normalized to 10% O2. NOx rose only moderately (by approximately 60 mg/m3). The findings show that targeted air transport and staging into the flame zone can substantially improve combustion completeness and boiler efficiency.