The researchers studied how burning lignite with a mix of oxygen and carbon dioxide affects the formation of nitrogen oxides (NO) compared to burning with air. They conducted experiments in a test unit and found that using 25% oxygen in the feed gas during oxy-combustion significantly reduces NO emissions compared to air combustion. The modeling results suggest that this reduction is due to increased destruction of NO. Changing the oxygen fraction or nitrogen content in the feed gas had minimal impact on NO formation during oxy-combustion.