Composition of Flue Gases during Oxy-Combustion of Energy Crops in a Circulating Fluidized Bed

In recent years, global warming and climate change associated with emissions of CO₂ from fossil fuel-fired power systems are a big worry for authorities in many countries worldwide. The utilization of biomass as an alternative, carbon-neutral fuel can reduce emissions of CO₂ and other greenhouse gases. Furthermore, the coupling of oxy-combustion of biomass with CO₂ capture is an option for carbon-negative power generation technology. In this study, emissions of NO_x, SO₂, and CO from the air- and oxy-combustion of three energy crops (Miscanthus giganteus, Sida hermaphrodita, and Salix viminalis) are presented and compared with emissions from other biomass fuels and reference coal. Combustion tests in air and O₂/CO₂ mixtures were conducted in a 12-kW bench-scale CFB combustor at 850 °C. Measurements of flue gas compositions were taken using an FTIR spectrometer. In all tested atmospheres, emissions of SO₂, N₂O, and CO for biomass were lower than those for the reference coal. The oxidation of volatile nitrogen compounds was behind high emissions of NO_x from biomass burned in air and O₂/CO₂ mixtures. The lowest concentrations of NO were found in the 21% O₂/70% CO₂ mixture. Combustion in mixtures containing more oxygen (30% and 40% O₂) led to a decrease in emissions of N₂O and CO and an increase in emissions of NO and SO₂.