Nitrogen-Bearing Emissions From Burning Corn Straw in a Fixed-Bed Reactor: Effects of Fuel Moisture, Torrefaction, and Air Flowrate

Combustion-generated emissions of acid gases, such as nitrogen-bearing species, constitute environmental pollutants and some are subjected to environmental regulations. Assessment of such emissions is important to decide what systems need to be put in place for their control. This applies to both conventional fossil fuels and for alternative environmentally friendlier fuels, such as renewable biomass. This research investigated the emissions of nitrogen-bearing gases, which evolve from combustion of biomass (corn straw) in a fixed bed furnace, as a function of specific air flowrate (⁠$m˙$_air) through the bed and of moisture content of the fuel. The effect of torrefaction of corn straw on the combustion-generated nitrogen bearing emissions was also examined. The predominant nitrogen-bearing species in the combustion effluents were hydrogen cyanide (HCN), nitrogen oxide (NO), and ammonia (NH₃). Increasing $m˙$_air through the bed, to enhance the combustion rate, increased the emissions of HCN, NO, and NH₃. As the $m˙$_air through the bed increased by a factor of 5, the amounts of HCN, NO, and NH₃ gases increased by factors of 3–4. As the moisture content of the biomass was reduced by drying, the combustion-generated emissions of NO increased mildly, whereas those of both NH₃ and HCN decreased. Furthermore, the combustion-generated emissions of NO and NH₃ from torrefied biomass were found to be higher than those from raw biomass. In contrast, the combustion-generated emissions of HCN from torrefied biomass were found to be lower than those generated from raw biomass.