Experimental study on synergistic emission reduction of PM and NO during ammonia-coal preheating co-firing

Ammonia-coal co-firing is a key approach to the low-carbon transition of coal-fired power plants. However, its large-scale application may face significant challenges due to the unclear and complex effects on particulate matter (PM) and nitrogen oxide (NO) formation. This study proposed an ammonia-coal preheating co-firing technology aimed at synergistically reducing PM and NO formation. At an ammonia blending ratio (denoted as α NH3 ) of 20%, preheating resulted in decreases of 17.15% in PM 1 , 9.45% in PM 1-10 , and 37.85% in NO, compared to conventional ammonia-coal co-firing. Meanwhile, at α NH3 = 20%, ammonia-coal preheating co-firing achieved reductions of 16.96%, 6.26%, and 20% for PM 10 , NO, and carbon dioxide (CO 2 ), respectively, relative to conventional pure coal combustion. The PM formation decreased as α NH3 increased from 0% to 40%. This reduction was primarily attributed to flue gas dilution due to ammonia combustion, while ammonia-coal interactions promoted PM formation. For NO, as α NH3 increased, its formation initially increased and then decreased, finally slightly increased, reaching a minimum at 20%. In the preheating zone, ammonia oxidizes more easily than coal, resulting in the highest NO formation at α NH3 = 10%. For α NH3 ≥ 20%, the variation in NO formation resulted from competition among ammonia oxidation, hydrogen cyanide (HCN) oxidation, and NO reduction through unburned ammonia and char. In summary, ammonia-coal preheating co-firing serves as a viable strategy for synergistically reducing PM 10 , NO, and CO 2 formation in coal-fired boilers.