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

ABSTRACT

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 NOx emissions from direct combustion or co-firing of algal biomass for energy utilization.