Emission and conversion of NO from algal biomass combustion in O₂/CO₂ atmosphere

Environmental impacts of NO emissions from biomass combustion have become an important concern. To address NO emission and conversion from algal biomass combustion in O₂/CO₂ atmosphere, three typical algal biomass, Chlorella (Ch), Enteromorpha (En), and Sargassum (Sa), were used to investigate NO emission characteristics in a one-dimensional tube furnace. The effects of the combustion temperature and O₂ concentration (21%, 25%, and 30%) on the NO emission were examined. It was found that the main peaks of NO positively are correlated to the O₂ concentration and combustion temperature. The NO emission trends of each algal biomass are slightly affected by the O₂ concentration at a given temperature. Roughly, the NO yield and conversion rate for each algal biomass increase with increasing O₂ concentration at a given temperature. They first increase with the increasing temperature and then decrease beyond 800 °C with exception for Sa in 30% O₂/CO₂ atmosphere. However, 21% O₂/CO₂ atmosphere is at least effective to reduce NO emission from most algal biomass combustion compared to air-based atmosphere (21% O₂/N₂), by 8.2-62.0%, 4.9-45.6%, and 22.5-59.6% for Ch, En, and Sa, respectively. The possible conversion pathway of fuel-N implies that the NO emission from algal biomass combustion in O₂/CO₂ atmosphere is the result of the combined effect of the NO formation oxidized from N-precursors and NO reduction by CO (converted from CO₂) and other reductive components. These results may provide a positive reference for the control of NO_x emissions from direct combustion or co-firing of algal biomass for energy utilization.